Court Opinion

ID: 9917022
Source: CourtListenerOpinion
Date Created: 2024-01-11 15:04:40.235593+00
Date Added: 2024-06-11T07:54:46.623799
License: Public Domain

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SJC-11693

                COMMONWEALTH   vs.   SHELDON MATTIS.

       Suffolk.      February 6, 2023. - January 11, 2024.

 Present:   Budd, C.J., Gaziano, Lowy, Cypher, Kafker, Wendlandt,
                           & Georges, JJ.

Homicide. Constitutional Law, Sentence, Cruel and unusual
     punishment, Parole. Parole. Practice, Criminal, Sentence,
     Parole.

     Indictments found and returned in the Superior Court
Department on December 21, 2011.

     Following review by this court, 484 Mass. 742 (2020),
findings of fact and a ruling of law were issued by Robert L.
Ullmann, J.

     Ryan M. Schiff (Paul R. Rudof & Ruth Greenberg also
present) for the defendant.
     Cailin M. Campbell, Special Assistant District Attorney
(John C. Verner, Assistant District Attorney, also present) for
the Commonwealth.
     The following submitted briefs for amici curiae:
     Darina Shtrakhman, of California, Matt K. Nguyen, of the
District of Columbia, & Adam Gershenson for Jeffrey Aaron &
others.
     Andrea Lewis Hartung, of Illinois, & Marsha L. Levick, of
Pennsylvania, & Oren Nimni for the Sentencing Project & others.
                                                                    2

     Jonathan W. Blodgett, District Attorney for the Eastern
District, & David F. O'Sullivan, Assistant District Attorney,
for District Attorney for the Eastern District & another.
     Jasmine Gonzales Rose, of Oregon, Duke K. McCall, III, &
Douglas A. Hastings, of the District of Columbia, Robert S.
Chang, of Washington, Caitlin Glass, Neda Khoshkhoo, & Katharine
Naples-Mitchell for Boston University Center for Antiracist
Research & others.
     Kenneth J. Parsigian, Avery E. Borreliz, Erin M. Haley, &
Martin W. Healy for Carol S. Ball & others.
     Benjamin H. Keehn, Committee for Public Counsel Services, &
John J. Barter for Committee for Public Counsel Services.

    BUDD, C.J.   When it comes to determining whether a

punishment is constitutional under either the Eighth Amendment

to the United States Constitution or art. 26 of the

Massachusetts Declaration of Rights, youth matters.    See, e.g.,

Miller v. Alabama, 567 U.S. 460 (2012); Graham v. Florida, 560

U.S. 48 (2010); Roper v. Simmons, 543 U.S. 551 (2005);

Diatchenko v. District Attorney for the Suffolk Dist., 466 Mass.

655 (2013) (Diatchenko I), S.C., 471 Mass. 12 (2015).     In

Miller, supra at 465, 476, the United States Supreme Court

struck down mandatory life imprisonment without the possibility

of parole for juveniles based in part on the "mitigating

qualities of youth."     Approximately one and one-half years

later, this court went further than Miller and concluded that

sentencing a juvenile to life without parole in any circumstance

would violate art. 26.    See Diatchenko I, supra at 669-670.

    The defendant, Sheldon Mattis, was convicted of murder in

the first degree, among other charges, and was sentenced to a
                                                                     3

mandatory term of life in prison without the possibility of

parole, see G. L. c. 265, § 2 (a).     Commonwealth v. Watt, 484

Mass. 742, 754-756 (2020).   On appeal, he challenged the

constitutionality of his sentence as applied to him.     He argued

that because he was eighteen years old at the time of the

murder, he is entitled to the same protection as juvenile

offenders (i.e., those from fourteen to seventeen years of age)

convicted of murder in the first degree, who receive a term of

life with the possibility of parole.    See G. L. c. 265, § 2 (b).

     Here, we consider whether our holding in Diatchenko I

should be extended to apply to emerging adults, that is, those

who were eighteen, nineteen, and twenty years of age when they

committed the crime.1   Based on precedent and contemporary

standards of decency2 in the Commonwealth and elsewhere, we

conclude that the answer is yes.3

     1 For the purposes of this opinion, "emerging adult" is
defined as someone who is eighteen, nineteen, or twenty years of
age. Although the record contains some references to
individuals who are as old as twenty-four years of age as
"emerging adults," the focus of the record and the Superior
Court judge's factual findings, which guide our analysis today,
are limited to offenders who are aged eighteen, nineteen, or
twenty at the time of the crime.

     2 As discussed infra, our understanding of contemporary
standards of decency is informed by the updated scientific
record.

     3 We acknowledge the amicus briefs submitted by (1) twenty-
three retired Massachusetts judges, Boston Bar Association, and
Massachusetts Bar Association; (2) seventeen neuroscientists,
                                                                          4

        Background.    1.   The homicide.   The evidence presented in

the defendant's trial is summarized in Watt, 484 Mass. at 744-

745.4       We provide a condensed version of events as the jury could

have found them.       On September 25, 2011, the defendant; his

codefendant, Nyasani Watt; and another friend observed Kimoni

Elliott standing outside a nearby convenience store.           Id. at

744.        The defendant approached Elliott on a bicycle and asked

him where he was from.       Elliott replied, "Everton."      Id.   The

two then parted ways.        Id.

        Elliott met Jaivon Blake in a nearby parking lot while the

defendant returned to Watt and said, "[B]e easy, because that's

them kids."       Watt, 484 Mass. at 744-745.    A few minutes later,

when Elliott and Blake were in view, the defendant handed Watt a

gun and told Watt "to go handle that."          Id. at 745.   Watt rode

toward Elliott and Blake on a bicycle and shot them from behind.

Id.     Elliott survived gunshot wounds to his neck and right arm,

psychologists, and criminal justice scholars; (3) Sentencing
Project, Juvenile Law Center, and Roderick and Solange MacArthur
Justice Center; (4) the Committee for Public Counsel Services;
(5) Boston University Center for Antiracist Research, Fred T.
Korematsu Center for Law and Equality, Center on Race,
Inequality, and the Law, and Criminal Justice Institute at
Harvard Law School; and (6) the district attorney for the
Eastern district and the district attorney for the Plymouth
district.

       The defendant and Watt were tried together, and their
        4

appeals were consolidated. The decision was published under
Watt's name.
                                                                       5

but Blake died from a single gunshot wound to the torso.        Id. at

744.

       2.    Procedural history and development of the record.    In

2013, the defendant and Watt were tried jointly and convicted of

murder in the first degree on the theories of deliberate

premeditation and extreme atrocity or cruelty, among other

charges.      Watt, who was seventeen at the time of the shooting,

received a life sentence with the possibility of parole after

fifteen years.5      Watt, 484 Mass. at 745.   See G. L. c. 265, § 2

(b).       See also G. L. c. 127, § 133A; G. L. c. 279, § 24.   The

defendant, who had turned eighteen approximately eight months

prior to the crime, received a life sentence without the

possibility of parole.       Watt, supra.   See G. L. c. 265, § 2 (a).

See also G. L. c. 127, § 133A.       Each defendant filed a motion

for a new trial.      Among other things, the defendant argued that

his mandatory sentence of life without parole violated art. 26's

prohibition of cruel or unusual punishment because he was under

twenty-two years of age when he committed the murder.       A

       Sentencing in this case occurred after the United States
       5

Supreme Court's decision in Miller, but mere days before we
issued our decision in Diatchenko I. Despite not yet having our
guidance on how to sentence such juveniles in the absence of new
legislation on the matter, the judge correctly sentenced Watt to
the equivalent penalty for murder in the second degree -- the
"next-most severe sentence under the sentencing statute"
available at the time for a juvenile convicted of murder in the
first degree. See Watt, 484 Mass. at 753.
                                                                    6

Superior Court judge denied both motions, and the appeals from

these denials were consolidated with the defendants' direct

appeals.   Watt, supra at 743-744.

     We unanimously upheld the denial of both defendants'

postconviction motions and affirmed all convictions.   Watt, 484

Mass. at 765.   However, we remanded the defendant's case6 to the

Superior Court for "development of the record with regard to

research on brain development after the age of seventeen[,

which] will allow us to come to an informed decision as to the

constitutionality of sentencing young adults to life without the

possibility of parole."   Id. at 756.

     A Superior Court judge, who had also been the trial judge,

conducted three days of evidentiary hearings during which three

expert witnesses -- neuroscientist Dr. Adriana Galván, forensic

psychologist7 Dr. Robert Kinscherff, and forensic psychologist

Dr. Stephen Morse -- testified on the topic of adolescent

neurological and psychological development after the age of

seventeen.8   The defendant also entered in the record the

     6 Because the art. 26 question did not apply to Watt, we
remanded only the defendant's case to the Superior Court. Watt,
484 Mass. at 765.

     7 "[F]orensic psychology [i]s the use of psychological
theories and methods and data to help the legal system resolve
legal questions."

     8 The parties agree that all of the experts who submitted
evidence in the record are duly qualified in the relevant fields
                                                                   7

transcript of the testimony of a fourth expert witness,

developmental psychologist Dr. Laurence Steinberg.9   The

of neuroscience and forensic psychology, among other
specialties, and are recognized as leaders in their respective
professional fields.

     Galván holds a Ph.D. in neuroscience and is a tenured
professor of psychology at the University of California, Los
Angeles (UCLA), as well as the director of UCLA's Developmental
Neuroscience Lab. She has coauthored over one hundred book
chapters and peer-reviewed studies, many of which have been
published in leading journals in her field. She has received
numerous honors and awards, including the Presidential Early
Career Award for Scientists and Engineers as well as the Troland
Award from the National Academy of Sciences.

     Kinscherff holds both a juris doctor and a Ph.D. in
clinical psychology. He is a professor in the doctoral
psychology program at William James College. He has been
qualified as an expert in forensic psychology numerous times and
was formerly the Assistant Commissioner for Forensic Mental
Health at the Department of Mental Health.

     Morse holds both a juris doctor and a Ph.D. in psychology
and social relations. He is a tenured professor of law and
professor of psychology and law at the University of
Pennsylvania. He has written numerous articles on neuroscience
and the law, many of which have been published in leading
journals on law and neuroscience. He has been qualified as an
expert in at least twenty cases and was previously the Legal
Director at the MacArthur Foundation's Law and Neuroscience
Project.

     Galván and Kinscherff testified on behalf of the defendant.
Morse testified on behalf of the Commonwealth.

     9 Steinberg holds a Ph.D. in human development and family
studies. He is a tenured professor at Temple University. Over
the course of forty years, he has authored scores of studies
that have been published in peer-reviewed journals, including
top journals in his field. He has been qualified as an expert
in developmental psychology approximately thirty times. His
research was cited in two of the leading Supreme Court cases on
the Eighth Amendment's ban on cruel and unusual punishment as
                                                                   8

Commonwealth and the defendant also submitted voluminous

exhibits, including numerous scientific studies on adolescence

and neurobiological maturity.

     The record was transmitted to us in May 2021 but did not

include factual findings.   In December 2021, we again remanded

this case, along with the case underlying our decision in

Commonwealth v. Robinson, 493 Mass.      (2023), to the Superior

Court for the development of factual findings based on the

previously transmitted record.10   Specifically, we requested

findings regarding "whether the imposition of a mandatory

sentence of life without the possibility of parole for . . .

those convicted of murder in the first degree who were eighteen

to twenty-one at the time of the crime, violates [art.] 26."

     A different Superior Court judge issued factual findings in

July 2022, concluding that the mandatory imposition of a

sentence of life without parole for offenders who were eighteen,

applied to juveniles. See Miller, 567 U.S. at 471 (referencing
Steinberg & Scott, Less Guilty by Reason of Adolescence:
Developmental Immaturity, Diminished Responsibility, and the
Juvenile Death Penalty, 58 Am. Psychologist 1009, 1014 [2003]);
Roper, 543 U.S. at 569-573 (same). Steinberg testified on
behalf of the defendant in the case underlying our decision in
Commonwealth v. Robinson, 493 Mass.     (2023), a case raising a
nearly identical sentencing claim. See note 10, infra.

     10This case was paired with the one underlying Robinson,
493 Mass.    , because, similarly to Mattis, Robinson asked this
court to consider whether a sentence of life without parole is
constitutional when applied to those who committed their crime
while under twenty-one years of age.
                                                                    9

nineteen, or twenty years old at the time they committed the

crime is a violation of art. 26.   In particular, the judge found

that emerging adults are "less able to control their impulses"

and that "their reactions in [emotionally arousing] situations

are more similar to those of [sixteen and seventeen year olds]

than they are to those [twenty-one to twenty-two] and older."

The case and its entire evidentiary record subsequently were

transmitted back to this court, where the defendant argued that

it is unconstitutional to sentence an emerging adult to life

without the possibility of parole in any circumstance, and the

Commonwealth argued that such a sentence is constitutional if

imposed after an individualized hearing.

     Discussion.   Adopted in 1780, art. 26 states:   "No

magistrate or court of law, shall . . . inflict cruel or unusual

punishments."   In evaluating the constitutionality of a

sentence, this court is guided by "[t]he fundamental imperative

of art. 26 that criminal punishment be proportionate to the

offender and the offense."   Diatchenko I, 466 Mass. at 671.    A

punishment is unconstitutional (i.e., cruel or unusual) if it is

so disproportionate to the crime that it "shocks the conscience

and offends fundamental notions of human dignity."    Id. at 669,

quoting Cepulonis v. Commonwealth, 384 Mass. 495, 497 (1981).11

     11Similarly, the Eighth Amendment's prohibition on cruel
and unusual punishment "flows from the basic 'precept of justice
                                                                    10

     1.   Constitutional framework.   To evaluate the

proportionality of a mandatory life sentence imposed on a

category of offenders (here, emerging adults), we look to

precedent as well as what contemporary standards of decency, as

defined by objective indicia, require.    See Graham, 560 U.S. at

61, quoting Roper, 543 U.S. at 563-564 ("The Court first

considers 'objective indicia of society's standards, as

expressed in legislative enactments and state practice,' to

determine whether there is a national consensus against the

sentencing practice at issue. . . .   [Then] guided by 'the

standards elaborated by controlling precedents and by the

Court's own understanding and interpretation of the Eighth

Amendment's text, history, meaning, and purpose,' . . . the

Court must determine . . . whether the punishment in question

violates the Constitution"); Roper, supra at 560-561.12    As for

that punishment for crime should be graduated and proportioned'
to both the offender and the offense." Miller, 567 U.S. at 469,
quoting Roper, 543 U.S. at 560.

     12The dissent asserts that the "tripartite" test is the
proper tool to analyze the constitutionality of the sentence
here. Post at     . See Commonwealth v. Jackson, 369 Mass. 904,
910-916 (1976). That test considers (1) the nature of the
offense and the offender in light of the degree of harm to
society, (2) the sentence imposed and penalties prescribed for
more serious crimes in Massachusetts, and (3) a comparison
between the sentence imposed with the penalties prescribed for
the same offense in other jurisdictions. It traditionally has
been used, both by this court and the Supreme Court, to assess
whether a term-of-years sentence is grossly disproportionate to
a given offense, considering all the circumstances of a
                                                                   11

the latter, current scientific consensus regarding the

characteristics of the class can help determine the contemporary

standards of decency pertaining to that class.   See Diatchenko

I, 466 Mass. at 659-661, 669-671.   See also Miller, 567 U.S. at

471-472 ("Our decisions rested not only on common sense . . .

but on science and social science as well"); Graham, supra at

68; Roper, supra at 569-570; Commonwealth v. Okoro, 471 Mass.

particular case. Id. See, e.g., Commonwealth v. Sharma, 488
Mass. 85, 89-90 (2021); Commonwealth v. LaPlante, 482 Mass. 399,
403 (2019); Commonwealth v. Perez, 477 Mass. 677, 685-686
(2017), S.C., 480 Mass. 562 (2018); Opinions of the Justices,
378 Mass. 822, 824-825 (1979). See also Ewing v. California,
538 U.S. 11 (2003); Harmelin v. Michigan, 501 U.S. 957 (1991);
Solem v. Helm, 463 U.S. 277 (1983).

     Although the tripartite test incorporates elements of the
approach we use today, it is of limited utility here. Its
"threshold comparison between the severity of the penalty and
the gravity of the crime does not advance the analysis" where
neither the sentence's proportionality to the charged offense
nor the existence of a more serious offense in the Commonwealth
is being challenged. See Graham, 560 U.S. at 61. Rather, our
cases show, and Supreme Court precedent affirms, that it is the
"categorical" framework, which focuses on contemporary standards
of decency, that applies here, where the task is to assess
whether a sentence is disproportionate when applied to an entire
category of offenders. See id. ("In cases turning on the
characteristics of the offender, the Court has adopted
categorical rules . . . [and] consider[ed] 'objective indicia of
society's standards'"); Diatchenko I, 466 Mass. at 669
(contemporary standards of decency render imposition of life
without parole sentence on particular category of offenders
unconstitutionally disproportionate). See also, e.g., Roper,
543 U.S. at 560-563 (standards of decency dictate death
penalty's unconstitutionality when imposed on those under
eighteen); Atkins v. Virginia, 536 U.S. 304, 321 (2002)
(standards of decency dictate death penalty's
unconstitutionality when imposed on those with intellectual
disabilities).
                                                                    12

51, 60 (2015) ("the determination that youth are

constitutionally distinct from adults for sentencing purposes

has strong roots in recent developments in the fields of science

and social science").

    a.     Precedent.   In a series of cases responding to

challenges to juvenile sentences, the Supreme Court has

consistently opined that the "mitigating qualities of youth"

must be taken into consideration when it comes to sentencing.

Johnson v. Texas, 509 U.S. 350, 367 (1993).     See, e.g., Jones v.

Mississippi, 141 S. Ct. 1307, 1314 (2021), citing Miller, 567

U.S. at 476; Johnson, supra ("A sentencer in a capital case must

be allowed to consider the mitigating qualities of youth in the

course of its deliberations over the appropriate sentence").

For example, when striking down the death penalty for juveniles

in Roper, the Court discussed the "relevance of youth as a

mitigating factor" at length, concluding that "[o]nce the

diminished culpability of juveniles is recognized, it is evident

that the penological justifications for the death penalty apply

to them with lesser force than to adults."     Roper, 543 U.S. at

570-571.

    In Graham, 560 U.S. at 76, the Court noted that an

"offender's age is relevant to the Eighth Amendment, and

criminal procedure laws that fail to take defendants'

youthfulness into account at all would be flawed."     The Court
                                                                     13

concluded that it was unconstitutional to sentence juveniles who

did not commit homicide to life without parole because they lack

the maturity to be classified among the worst offenders

deserving of the harshest punishments.    The Court further noted

that although "[m]aturity can lead to that considered reflection

which is the foundation for remorse, renewal, and rehabilitation

. . . [a] young person who knows that he or she has no chance to

leave prison before life's end has little incentive to become a

responsible individual."13   Id. at 79.

     More recently in Miller, 567 U.S. at 476, in which the

Court held that a judge must be able to consider "mitigating

qualities of youth" in formulating a sentence, the Court

reiterated that youth is not simply a "chronological fact"

(citation omitted).    Rather, "[i]t is a time of immaturity,

irresponsibility, impetuousness[,] and recklessness. . . .      It

is a moment and condition of life when a person may be most

susceptible to influence and to psychological damage. . . .     And

its signature qualities are all transient" (citations and

quotations omitted).   Id.   As a result, the Court reasoned, the

Eighth Amendment forbids a sentencing scheme that mandates life

     13Although Graham's ban on life sentences without the
possibility of parole for juveniles applied only to nonhomicide
crimes, as the Miller Court pointed out, "none of what [Graham]
said about children -- about their distinctive (and transitory)
mental traits and environmental vulnerabilities -- is crime-
specific." Miller, 567 U.S. at 473.
                                                                  14

without parole for juvenile offenders because such a scheme

precludes a consideration of youth and the circumstances and

characteristics attendant to it.    Id. at 479.

    Approximately one and one-half years after Miller was

decided, we considered whether sentencing a juvenile offender to

life without the possibility of parole comported with art. 26.

See Diatchenko I, 466 Mass. at 661.    Ultimately, this court went

further than Miller and concluded that because it is not

possible to demonstrate that a juvenile offender is

"irretrievably depraved," under the Massachusetts Declaration of

Rights, such a sentence is cruel or unusual as imposed on a

juvenile in any circumstance.   Id. at 670-671.

    Central to each of the foregoing cases is the "fundamental

precept of justice that punishment for crime should be graduated

and proportioned to both the offender and the offense" (citation

and quotations omitted).   Id. at 669.      Until now, we have

declined to consider extending Diatchenko I to offenders

eighteen years of age and older.    See Watt, 484 Mass. at 755-

756, and cases cited.   However, we also recognized that

"researchers continue to study the age range at which most

individuals reach adult neurobiological maturity . . . and that

such research may relate to the constitutionality of sentences

of life without parole for individuals other than juveniles"

(citation and quotation omitted).     Id.   The judge's findings in
                                                                     15

this case, described more fully infra, confirm that the brains

of emerging adults are similar to those of juveniles.

    b.   Contemporary standards of decency.    An assessment of a

punishment's proportionality occurs "in light of contemporary

standards of decency which mark the progress of society."

Diatchenko I, 466 Mass. at 669, quoting Good v. Commissioner of

Correction, 417 Mass. 329, 335 (1994).    See Okoro, 471 Mass. at

61 (proportionality of punishment is determined based on "the

evolving standards of decency that mark the progress of a

maturing society" [citation omitted]).    Here, we consider the

updated research on the brains of emerging adults, as well as

the way emerging adults are treated in the Commonwealth and

elsewhere, to determine whether a sentence of life without the

possibility of parole is proportionate and thus constitutional

when imposed upon that class of offenders.

    i.   Science and social science.     As mentioned supra, where

modern scientific consensus regarding a particular class exists,

it can be useful in determining the contemporary standards of

decency as they relate to that class.    See Miller, 567 U.S. at

471-472; Okoro, 471 Mass. at 59-60.

    Advancements in scientific research have confirmed what

many know well through experience:    the brains of emerging

adults are not fully mature.   Specifically, the scientific

record strongly supports the contention that emerging adults
                                                                  16

have the same core neurological characteristics as juveniles

have.     As the Superior Court judge noted, "Today,

neuroscientists and behavioral psychologists know significantly

more about the structure and function of the brains of

[eighteen] through [twenty year olds] than they did [twenty]

years ago . . . ."    This is the result of years of targeted

research and greater access to relatively new and sophisticated

brain imaging techniques, such as structural magnetic resonance

imaging (sMRI) and functional magnetic resonance imaging

(fMRI).14    From the detailed evidence produced in the record, the

judge made four core findings of fact regarding the science of

emerging adult brains:    emerging adults (1) have a lack of

impulse control similar to sixteen and seventeen year olds in

emotionally arousing situations,15 (2) are more prone to risk

taking in pursuit of rewards than those under eighteen years and

those over twenty-one years, (3) are more susceptible to peer

     14 sMRIs allow researchers to examine the brain's anatomical
structures at particular moments in time; fMRIs allow
researchers to examine the brain's activation and responses to
stimuli and environmental context. As Galván testified, MRIs,
particularly sMRIs, have allowed researchers "to see [a] fine
grain view of the brain that other technologies would not
allow."

     15This also is referred to as being under "hot cognition."
The experts testified that under "cold cognition," which is the
absence of emotionally arousing circumstances, the emerging
adult brain functions much more similarly to the older adult
brain than to the adolescent brain.
                                                                  17

influence than individuals over twenty-one years, and (4) have a

greater capacity for change than older individuals due to the

plasticity of their brains.    The driving forces behind these

behavioral differences are the anatomical and physiological

differences between the brains of emerging and older adults.

See Steinberg, A Social Neuroscience Perspective on Adolescent

Risk-Taking, 28 Developmental Rev. 78, 82-84, 85-89 (2008).

These structural and functional differences make emerging

adults, like juveniles, "particularly vulnerable to risk-taking

that can lead to poor outcomes."

    We discuss each of the judge's four core factual findings

in turn.

    A.     Impulse control.   The judge found that in terms of

impulse control, emerging adults are more similar to sixteen and

seventeen year old juveniles than to older adults.    That is,

they are less able to control their impulses in emotionally

arousing situations.   This finding is well supported by the

record.

    Emerging adults still are experiencing the effects of "the

sharp increase during puberty of certain hormones," lack a fully

developed prefrontal cortex, which is "the part of the brain

that most clearly regulates impulses," and lack fully developed

connections "between the prefrontal cortex and other parts of

the brain . . . that most clearly respond[] to rewards and
                                                                  18

reward-related decision making."   All four experts agreed that

compared to older adults, emerging adults are more impulsive,

more concerned with their immediate circumstances, and less able

to envision future consequences.   Galván explained that at least

part of this distinction between emerging and older adults can

be traced to differences in brain structure between the groups.

"[T]he prefrontal cortex is the home for these abilities that we

might say are what makes us adults . . . the ability to reason,

the ability to think about how your actions today will have

implications for the future."   As the brain matures, it

"undergoes a process called pruning and [eliminates]" synapses

and neurons that are not needed.   Advancements in sMRI data have

allowed researchers "to measure this cortical thickness and

thinning and the process continues through [eighteen],

[nineteen], [twenty] years old."

    All of the other experts, including the Commonwealth's

expert, agreed that the prefrontal cortex, an area of the brain

associated with controlling impulses, is among the last brain

regions to develop, and continues developing until the early to

mid-twenties.   See Icenogle et al., Adolescents' Cognitive

Capacity Reaches Adult Levels Prior to Their Psychosocial

Maturity:   Evidence for a "Maturity Gap" in a Multinational,

Cross-Sectional Sample, 43 Law & Hum. Behav. 69, 70 (2019);

Sowell & others, In Vivo Evidence for Post-Adolescent Brain
                                                                   19

Maturation in Frontal and Striatal Regions, 2 Nature Neurosci.

859, 860-861 (1999); Steinberg et al., Around the World,

Adolescence Is a Time of Heightened Sensation Seeking and

Immature Self-Regulation, Developmental Sci., vol. 21, Mar.

2018, at 1-4, 15-17.

    B.    Risk taking in pursuit of reward.   The judge found that

"[a]s a group, [individuals eighteen through twenty years of

age] in the United States and other countries are more prone to

'sensation seeking,' which includes risk-taking in pursuit of

rewards, than are individuals under age [eighteen] and over age

[twenty-one]."   This finding similarly is well supported by the

record.

    All of the experts agreed that emerging adults are more

likely than children or older adults to engage in risky behavior

and that risky behaviors tend to peak in late adolescence to

early adulthood and then decline, with some experts asserting

that this behavior plateaus around twenty-two years of age.

Galván explained that fMRI studies evaluating the brain have

shown that in individuals at least seventeen years of age, and

up to twenty-one years of age, there is greater activity in the

nucleus accumbens, a part of the brain associated with sensation

seeking, than in older adults.   Additionally, fMRI studies have

shown that the ventral striatum, a part of the brain that

correlates with risk-taking behaviors, also is more active among
                                                                   20

late adolescents and early adults than it is in older adults.

This research tracks numerous real-world behaviors.     Emerging

adults are overrepresented in multiple types of risky behavior,

such as risky sexual behavior and risky driving behavior, in

addition to risky criminal behavior.   See Roper, 543 U.S. at

569, quoting Arnett, Reckless Behavior in Adolescence:    A

Developmental Perspective, 12 Developmental Rev. 339 (1992) ("It

has been noted that 'adolescents are overrepresented

statistically in virtually every category of reckless

behavior'").

     Each expert discussed the so-called "age-crime curve,"

which is a widely recognized phenomenon illustrating that

criminal behavior crests at some point from late adolescence to

early adulthood before significantly declining.   Put succinctly,

as with those under eighteen years of age, "late adolescence[16]

     16All the experts referred to individuals from eighteen to
twenty years of age as "late adolescents." We refer to this age
group as "emerging adults." We do not agree with the dissent
that this appellation indicates that we improperly are veering
into the Legislature's lane. As the Supreme Court noted when it
declared the death penalty unconstitutional for juveniles, line
drawing is a necessary task when considering categorical bans on
unconstitutional sentences. Roper, 543 U.S. at 574 ("Drawing
the line at [eighteen] years of age is subject, of course, to
the objections always raised against categorical rules. The
qualities that distinguish juveniles from adults do not
disappear when an individual turns [eighteen]. By the same
token, some under [eighteen] have already attained a level of
maturity some adults will never reach. For the reasons we have
discussed, however, a line must be drawn").
                                                                   21

is a period in human development of increased risk taking,

greater reactivity to high stress or highly emotionally arousing

events and certain kinds of cognitive biases that, for example,

lead them [(i.e., juveniles and emerging adults)] to not

appraise a risk and apply it to themselves in the same way that

an adult would."   See Galván et al., Earlier Development of the

Accumbens Relative to Orbitalfrontal Cortex Might Underlie Risk-

Taking Behaviors in Adolescents, 26 J. Neurosci. 6885, 6885-6892

(2006); Hawes et al., Modulation of Reward-Related Neural

Activation on Sensation Seeking across Development, 283

NeuroImage 763, 763-771 (2017); Rudolph et al., At Risk of Being

Risky:   The Relationship Between "Brain Age" under Emotional

States and Risk Preference, Developmental Cognitive Neurosci.,

vol. 24, 2017, at 93-106; Steinberg et al., Around the World,

Adolescence Is a Time of Heightened Sensation Seeking and

Immature Self-Regulation, supra at 1-4, 15-17.

    C.   Peer influence.   The judge also found that emerging

adults "are more susceptible to peer influence" than older

adults and that the presence of peers makes emerging adults

"more likely to engage in risky behavior."   All four experts

agreed that current research supports this conclusion.

    Steinberg's research in particular focuses on the ways in

which the presence of peers affects decision-making and risk

taking among different age groups.   In his work, he has found
                                                                   22

that "even if the peers aren't explicitly encouraging anything,

the mere presence of peers increases the likelihood that

adolescents[17] will engage in [risky] behavior."   Although the

presence of peers may influence behavior at any age, "peer

influence is a much more serein [sic] and powerful factor during

adolescence[18] than it is during adulthood."   See Breiner et al.,

Combined Effects of Peer Presence, Social Cues, and Rewards on

Cognitive Control in Adolescents, 60 Developmental Psychobiology

292, 292-302 (2018); Galván, Adolescent Brain Development and

Contextual Influences:    A Decade in Review, 31 J. Res. on

Adolescence 843, 852-853 (2021); Silva et al., Peers Increase

Late Adolescents' Exploratory Behavior and Sensitivity to

Positive and Negative Feedback, 26 J. Res. on Adolescence 696,

696-705 (2015).

     D.    Capacity for change.   Finally, the judge found that

emerging adults "have greater capacity to change than older

individuals because of the plasticity of the brain during these

years."    This finding is well supported by the record.

     "[P]lasticity refers to the ability [to] change in response

to the environment."19    Although the brain has its greatest

     17   See note 16, supra.

     18   See note 16, supra.

     19Galván explained that plasticity primarily occurs in the
hippocampus, which is "a small brain region in the deep layers
                                                                   23

plasticity in the early months of life, as Galván explained,

"[t]he second wave [of plasticity] is during adolescence."20    In

contrast, "adult capacity for change is diminished because" the

fully mature brain is much less malleable.    Although the brain

continues to change throughout one's lifespan, Steinberg

testified that brain maturation is largely complete by as early

as twenty-two years of age, and possibly up to twenty-five years

of age.    The Commonwealth's expert agreed that "[m]ost

adolescents[21] even those who commit serious crimes will age out

of offending and will not become career criminals."    See Roper,

543 U.S. at 570, quoting Johnson, 509 U.S. at 368, and citing

Steinberg & Scott, Less Guilty by Reason of Adolescence:

Developmental Immaturity, Diminished Responsibility, and the

Juvenile Death Penalty, 58 Am. Psychologist 1009, 1014 (2003)

("the signature qualities of youth are transient; as individuals

mature, the impetuousness and recklessness that may dominate in

younger years can subside").    See also Cauffman et al., A

Developmental Perspective on Adolescent Risk-Taking and Criminal

Behavior, c. 6 in The Handbook of Criminological Theory (2015);

of the brain that has mostly been studied in the context of
learning because plasticity or any plasticity-based changes are
because we've learned something new."

     20   See note 16, supra.

     21   See note 16, supra.
                                                                   24

Galván, Insights about Adolescent Behavior, Plasticity, and

Policy from Neuroscience Research, 83 Neuron 262, 264 (2014).

    The evidence outlined supra provides a scientifically

informed view of emerging adults' culpability and factors into

our analysis whether contemporary standards of decency permit

sentencing that cohort to life without the possibility of

parole.

    ii.   Treatment of emerging adults in the Commonwealth and

elsewhere.   To determine our contemporary standards of decency,

in addition to referring to our own State statutes, see Good,

417 Mass. at 335, we may look to other policies and programs in

the Commonwealth, our precedent, other States' statutes, as well

as other States' judicial rulings, and even international

statutes and decisions, among other sources, see Okoro, 471

Mass. at 61 (we commonly look to "judicial opinions and

legislative actions at the State, Federal, and international

levels," which "help to inform our understanding of what art. 26

protects" [citation omitted]).   See also Thompson v. Oklahoma,

487 U.S. 815, 821-831 (1988) (looking to State statutes and

death penalty juries to divine contemporary standards of

decency, and noting consistency with practices of other

nations); Enmund v. Florida, 458 U.S. 782, 788 (1982) (looking

to "historical development of the punishment at issue,

legislative judgments, international opinion, and the sentencing
                                                                   25

decisions juries have made"); Coker v. Georgia, 433 U.S. 584,

596 (1977) ("important to look to the sentencing decisions that

juries have made in the course of assessing whether capital

punishment is an appropriate penalty").    As discussed infra, a

combination of statutes passed here and elsewhere, as well as

recent decisions in Washington and Michigan, indicate that our

contemporary standards of decency do not support imposing life

without parole sentences on emerging adults.

    To begin, the Legislature has determined that emerging

adults require different treatment from older adults,

specifically in the penological context.   For example, the

Department of Youth Services (department) statutorily is

authorized to maintain custody of young people adjudicated as

youthful offenders up to twenty-one years of age.     See

Commonwealth v. Terrell, 486 Mass. 596, 599-600, 603 (2021);

G. L. c. 119, § 58.   This sentencing scheme also permits the

imposition of "dual" sentences for youthful offenders, requiring

them to remain in the department's custody until they are

twenty-one years of age before beginning their "adult sentence"

at a house of correction.   G. L. c. 119, § 58 (b).

    Further, in 2018, as part of a set of sweeping reforms, the

Legislature authorized the Department of Correction and county

houses of correction to "establish young adult correctional

units."   These units provide "targeted interventions, age
                                                                    26

appropriate programming and a greater degree of individual

attention" for individuals in custody "ages [eighteen] to

[twenty-four]."    G. L. c. 127, § 48B (a).   Notably, the

Legislature also formed the Task Force on Emerging Adults in the

Criminal Justice System (task force), which released a report in

2020 concluding that emerging adults "are a unique population

that requires developmentally-tailored programming and

services."22    Emerging Adults in the Massachusetts Criminal

Justice System:    Report of the Task Force on Emerging Adults in

the Criminal Justice System (Feb. 26, 2020), 2020 Senate Doc.

No. 2840, at 6.    See St. 2018, c. 69, § 221.

     Massachusetts is not alone in recognizing that emerging

adult offenders require different treatment from older adult

offenders.     For example, the District of Columbia now provides a

     22 Noting that the dual sentencing scheme for youthful
offenders under G. L. c. 119, § 58, applies only to juveniles,
and that the task force's recommendations for emerging adults do
not include offenders convicted of murder in the first degree,
Justice Lowy's dissent concludes that neither demonstrates
contemporary standards of decency here in the Commonwealth.
Post at     . See G. L. c. 119, § 74; Emerging Adults in the
Massachusetts Criminal Justice System: Report of the Task Force
on Emerging Adults in the Criminal Justice System (Feb. 26,
2020), 2020 Senate Doc. No. 2840, at 10. To the contrary, both
examples demonstrate that the Legislature and other community
members recognize that emerging adult offenders benefit from
being treated differently from older adult offenders. Cf.
Thompson v. Oklahoma, 487 U.S. 815, 823 (1988) (distinct
treatment of younger juveniles compared to older juveniles "in
criminal sanctions and rehabilitation" is evidence of
contemporary standards of decency [citation omitted]).
                                                                     27

chance at sentence reduction for people who were under twenty-

five years old when they committed a crime.    D.C. Code § 24-

403.03.   In 2019, Illinois enacted a law allowing parole review

at ten or twenty years into a sentence for most crimes,

exclusive of sentences to life without parole, if the individual

was under twenty-one years old at the time of the offense.         730

Ill. Comp. Stat. 5/5-4.5-115.    Effective January 1, 2024,

Illinois also ended life without parole for most individuals

under twenty-one years old, allowing review after they serve

forty years.   Ill. Pub. L. No. 102-1128, § 5 (2022).   California

has extended youth offender parole eligibility to individuals

who committed offenses before twenty-five years of age.       Cal.

Penal Code § 3051.    Similarly, in 2021, Colorado expanded

specialized program eligibility, usually reserved for juveniles,

to adults who were under twenty-one when they committed a

felony.   Colo. House Bill No. 21-1209 (2021) (enacted).      In

Wyoming, "youthful offender" programs were revised to offer

reduced and alternative sentencing for those under thirty years

old.   Wyo. Stat. Ann. §§ 7-13-1002, 7-13-1003.

       Legislation outside of the penological context is also

instructive in ascertaining contemporary standards of decency.

In Thompson, 487 U.S. at 838, the Supreme Court determined that

the death penalty was unconstitutional when imposed on a fifteen

year old offender based, in part, on then-current nonpenological
                                                                   28

State statutes that treated younger juveniles differently from

those closer to age eighteen.   Among other things, the Court

noted that "in all but one State a [fifteen]-year-old may not

drive without parental consent, and in all but four States a

[fifteen]-year-old may not marry without parental consent"

(footnote omitted).   See id. at 824-825.

     Similarly, Massachusetts, like most States, distinguishes

emerging adults from older adults on a range of issues, granting

rights and imposing responsibilities in a graduated manner.     For

example, one must be eighteen years of age to enter binding and

enforceable contracts, to sit on a jury, to purchase lottery

tickets, and to drive a common carrier motor vehicle.23   See

G. L. c. 231, § 85O; G. L. c. 234A, § 4; G. L. c. 10, § 29;

G. L. c. 159A, § 9.   However, one must be twenty-one years of

age to purchase and sell alcoholic beverages, to purchase

tobacco products, to obtain a license to carry a handgun, to be

a police officer, and to gamble.   See G. L. c. 138, § 34; G. L.

c. 270, § 6; G. L. c. 140, § 131 (d) (iv); G. L. c. 31, § 58;

G. L. c. 22C, § 10; G. L. c. 23K, §§ 25 (h), 43.   These statutes

reflect the commonly held view that emerging adults generally

     23Moreover, young adults who have reached eighteen years of
age may "continue to be considered 'minors'" for purposes of
parental support. Eccleston v. Bankosky, 438 Mass. 428, 429
(2003), quoting Stolk v. Stolk, 31 Mass. App. Ct. 903, 904-905
(1991). See G. L. c. 208, § 28.
                                                                   29

are not equipped to assume all the responsibilities of

adulthood, especially with respect to high risk activities.     Cf.

Thompson, 487 U.S. at 824-825.

    We are not the first State Supreme Court to appreciate the

distinct ways in which our laws bear on emerging adults.

Recently, the high courts in Washington and Michigan prohibited

the mandatory imposition of life without the possibility of

parole for those who are from eighteen to twenty years of age,

and for those who are eighteen years of age, respectively.    In

Matter of the Personal Restraint of Monschke, 197 Wash. 2d 305

(2021), the Supreme Court of Washington considered evolving

standards of decency, updated brain science, and precedent to

conclude that mandatory sentences of life without parole violate

the Washington Constitution when meted out to those under

twenty-one when they committed the crime.   See id. at 325-326.

    One year later, the Supreme Court of Michigan looked at the

issue as it pertained to eighteen year old offenders.    The court

reasoned that because "the Eighth Amendment dictates that youth

matters in sentencing," and because brain science has

demonstrated that eighteen year old individuals possess the same

attributes of youth as do juveniles, mandatorily subjecting an

eighteen year old defendant to life in prison is "unusually

excessive imprisonment and thus a disproportionate sentence that

constitutes 'cruel or unusual punishment' under [the Michigan
                                                                  30

Constitution]."   People v. Parks, 510 Mich. 225, 234, 255

(2022).24

     Twenty-two States and the District of Columbia do not

mandate life without parole in any circumstance.25   Of the

remaining twenty-eight States, only twelve (including

Massachusetts) mandate life without parole.26   Moreover, the

     24However, both the Washington and Michigan courts
determined that a sentence of life without the possibility of
parole could be imposed on young adult offenders after an
individualized sentencing hearing to consider the offender's
youth. See Parks, 510 Mich. at 240-241; Matter of the Personal
Restraint of Monschke, 197 Wash. 2d at 327-328.

     25In those twenty-two States and the District of Columbia,
the highest penalties are imposed only on discretionary bases.
See Alaska Stat. § 12.55.125; D.C. Code § 22-2104; Ga. Code Ann.
§ 16-5-1; Idaho Code Ann. §§ 18-4004, 19-2515; 720 Ill. Comp.
Stat. 5/9-1; Ind. Code §§ 35-50-2-3, 35-50-2-9; Ky. Rev. Stat.
Ann. § 532.030; Me. Rev. Stat. tit. 17-A, § 1603; Md. Code Ann.,
Crim. Law §§ 2-201, 2-203; Mont. Code Ann. § 45-5-102(2); Nev.
Rev. Stat. § 200.030(4)(a)-(b); N.M. Stat. Ann. § 31-18-13; N.Y.
Penal Law §§ 60.06, 70.00(5); N.D. Cent. Code § 12.1-32-01; Ohio
Rev. Code Ann. §§ 2929.02, 2929.04; Okla. Stat. tit. 21,
§ 701.9; Or. Rev. Stat. § 163.107; R.I. Gen. Laws §§ 11-23-2,
12-19.2-1 to 12-19.2-5; S.C. Code Ann. § 16-3-20; Tenn. Code
Ann. § 39-13-204; Utah Code Ann. § 76-5-203; Wis. Stat.
§ 973.014(1g)(c)-(2); Wyo. Stat. Ann. § 6-2-101.

     26See G. L. c. 265, § 2 (a) ("any person who is found
guilty of murder in the first degree shall be punished by
imprisonment in the state prison for life and shall not be
eligible for parole pursuant to [G. L. c. 127, § 133A"); Colo.
Rev. Stat. § 18-1.3-401(1)(a)(V)(F), (4)(a)(I)-(II) ("A person
. . . shall be punished by life imprisonment" without
possibility of parole); Del. Code Ann. tit. 11, § 4209 ("Any
person who is convicted of first-degree murder for an offense
that was committed after the person had reached [his or her]
eighteenth birthday shall be punished by . . . imprisonment for
the remainder of the person's natural life without benefit of
probation or parole or any other reduction"); Haw. Rev. Stat.
                                                                   31

statutes in at least two of those States provide an opportunity

to avoid the mandatory nature of the sentence.27   Twelve States

mandate life without parole as an alternative to a discretionary

death sentence,28 and five States only mandate life without

§ 706-656 ("Persons eighteen years of age or over at the time of
the offense who are convicted of first degree murder or first
degree attempted murder shall be sentenced to life imprisonment
without the possibility of parole"); Iowa Code § 902.1 (on
conviction of murder in first degree, "the court shall . . .
commit the defendant . . . for the rest of the defendant's life
. . . [and the defendant] shall not be released on parole unless
the governor commutes the sentence to a term of years"); Mich.
Comp. Laws § 750.316 (any person "who commits . . . first degree
murder . . . shall be punished by imprisonment for life without
eligibility for parole"); Minn. Stat. § 609.106 ("the court
shall sentence a person to life imprisonment without possibility
of release . . . [if] the person is convicted of first-degree
murder"); N.H. Rev. Stat. Ann. § 630:1-a(III) ("A person
convicted of a murder in the first degree shall be sentenced to
life imprisonment and shall not be eligible for parole at any
time"); 18 Pa. Cons. Stat. § 1102 ("a person who has been
convicted of a murder of the first degree . . . shall be
sentenced to . . . a term of life imprisonment"); Va. Code Ann.
§ 18.2-10(a) ("Any person who was [eighteen] years of age or
older at the time of the offense and who is sentenced to
imprisonment for life upon conviction of a Class 1 felony shall
not be eligible for . . . parole"); Wash. Rev. Code § 10.95.030
(any person "convicted of the crime of aggravated first degree
murder shall be sentenced to life imprisonment without
possibility of release or parole"); W. Va. Code § 61-2-2
("Murder of the first degree shall be punished by confinement in
the penitentiary for life").

     27Iowa allows its Governor to commute the sentence to a
term of years. Iowa Code § 902.2. Hawaii obligates the parole
board to submit an application to its Governor to commute the
sentence to one permitting parole after twenty years. Haw. Rev.
Stat. § 706-656.

     28See Ala. Code § 13a-6-2(c); Ariz. Rev. Stat. Ann. §§ 13-
751(A), 13-1105(D); Ark. Code Ann. § 5-10-101(c); Fla. Stat.
§ 775.082; Kan. Stat. Ann. § 21-6617 (for capital murder); La.
                                                                    32

parole if aggravating circumstances exist.29   Massachusetts is

one of only ten States that currently require eighteen through

twenty year old individuals who are convicted of murder in the

first degree to be sentenced to life without parole.

     We also may consider where other nations stand in this

analysis.   See Okoro, 471 Mass. at 61.   See also Graham, 560

U.S. at 80 ("The judgments of other nations and the

international community are not dispositive as to the meaning of

the Eighth Amendment," but "[t]he Court has looked beyond our

Nation's borders for support for its independent conclusion that

a particular punishment is cruel and unusual").   The United

Kingdom has banned life without parole for any offender under

twenty-one years of age at the time of the offense.    Sentencing

Act 2020, c. 17, § 322, sch. 21, par. 2 (U.K.).    And in 2022,

the Supreme Court of Canada unanimously ruled that life without

parole sentences were unconstitutional for all offenders,

regardless of age.   R. v. Bissonnette, 2022 SCC 23.   The

foregoing examples suggest that the "evolving standards of

decency that mark the progress of a maturing society" referenced

Rev. Stat. Ann. § 14:30(C); Miss. Code Ann. §§ 47-7-3(1)(d), 97-
3-21; Mo. Rev. Stat. § 565.020; Neb. Rev. Stat. § 28-105; N.C.
Gen. Stat. § 14-17; S.D. Codified Laws § 22-6-1; Tex. Penal Code
Ann. § 12.31.

     29See Cal. Penal Code § 190.2; Conn. Gen. Stat. §§ 53a-
35a(1)(B), 53a-54b; N.J. Stat. Ann. § 2C:11-3; Va. Code Ann.
§§ 18.2-10, 18.2-31; Vt. Stat. Ann. tit. 13, § 2303.
                                                                     33

in Miller, 567 U.S. at 469, trend away from life without parole

for emerging adults (citation omitted).

       2.   Life without parole for emerging adults violates art.

26.    Our comprehensive review informs us that Supreme Court

precedent, as well as our own, dictates that youthful

characteristics must be considered in sentencing, that the

brains of emerging adults are not fully developed and are more

similar to those of juveniles than older adults, and that our

contemporary standards of decency in the Commonwealth and

elsewhere disfavor imposing the Commonwealth's harshest sentence

on this cohort.       Consequently, we conclude that a sentence of

life without the possibility of parole for emerging adult

offenders violates art. 26.30      See Diatchenko I, 466 Mass. at

670.

       3.   Remedy.   Because we have determined that it is

unconstitutional to sentence emerging adults to life without the

possibility of parole, we invalidate those provisions of our

       The contemporary standards of decency that govern our
       30

decision today do not suggest a societal consensus that those
aged twenty-one and above should be treated differently from
older adults. Thus, while we acknowledge that the scientific
record in this case suggests that the unique attributes of youth
may persist in young adults older than twenty-one, our art. 26
proportionality analysis does not rely on science alone. See
Libby v. Commissioner of Correction, 385 Mass. 421, 435 (1982),
quoting District Attorney for the Suffolk Dist. v. Watson, 381
Mass. 648, 661-662 (1980) ("Article 26, like the Eighth
Amendment, bars punishments which are 'unacceptable under
contemporary moral standards'").
                                                                    34

criminal code that deny the possibility of parole to this

cohort.   General Laws c. 265, § 2, which was amended after

Diatchenko I was decided, sets forth the penalty for murder in

the first degree, distinguishing between the penalties for

adults and juveniles:

    "(a) Except as provided in subsection (b), any person who
    is found guilty of murder in the first degree shall be
    punished by imprisonment in the [S]tate prison for life and
    shall not be eligible for parole pursuant to [G. L. c. 127,
    § 133A].

    "(b) Any person who is found guilty of murder in the first
    degree who committed the offense on or after the person's
    fourteenth birthday and before the person's eighteenth
    birthday shall be punished by imprisonment in the [S]tate
    prison for life and shall be eligible for parole after the
    term of years fixed by the court pursuant to [G. L. c. 279,
    § 24]."

Although we hold that it is unconstitutional to sentence

individuals from eighteen to twenty years of age to life without

the possibility of parole, we must "as far as possible, . . .

hold the remainder [of the statute] to be constitutional and

valid, if the parts are capable of separation and are not so

entwined that the Legislature could not have intended that the

part otherwise valid should take effect without the invalid

part."    Diatchenko I, 466 Mass. at 672, quoting Boston Gas Co.

v. Department of Pub. Utils., 387 Mass. 531, 540 (1982).      See

G. L. c. 4, § 6, Eleventh ("The provisions of any statute shall

be deemed severable, and if any part of any statute shall be

adjudged unconstitutional or invalid, such judgment shall not
                                                                    35

affect other valid parts thereof").31    Here, because emerging

adults do not fit within the exception described in G. L.

c. 265, § 2 (b), we must invalidate that portion of G. L.

c. 265, § 2 (a), that denies parole eligibility to those from

eighteen to twenty years old.    See Diatchenko I, supra at 673.

Likewise, we also must invalidate that portion of the parole

statute, G. L. c. 127, § 133A, that denies parole to those from

eighteen to twenty years of age.32

     Because the Legislature does not currently provide a parole

eligibility scheme for this category of offenders, we look to

the next-most severe sentence under the sentencing scheme to

determine the floor of parole eligibility.    See Watt, 484 Mass.

at 753-754, citing Diatchenko I, 466 Mass. at 672-673.    For

emerging adults convicted of murder in the first degree on or

     31Notably, the Legislature specifically provides for the
severability of G. L. c. 265, § 2. See St. 1982, c. 554, § 7
("If any of the provisions of [G. L. c. 265, § 2,] or the
application thereof to any person or circumstances is held
invalid, such invalidity shall not affect other provisions or
applications of this act which can be given effect without the
invalid provisions or applications, and to this end the
provisions of this act are declared severable").

     32   General Laws c. 127, § 133A, states in relevant part:

     "Every prisoner who is serving a sentence for life in a
     correctional institution of the commonwealth, . . . except
     prisoners serving a life sentence for murder in the first
     degree who had attained the age of [eighteen] years at the
     time of the murder . . . shall be eligible for parole at
     the expiration of the minimum term fixed by the court under
     [G. L. c. 279, § 24]."
                                                                   36

after today's decision, that means applying G. L. c. 279, § 24,

as amended through St. 2014, c. 189, § 6, which sets parole

eligibility for juvenile offenders who have committed murder in

the first degree:

    "In the case of a sentence of life imprisonment for murder
    in the first degree committed by a [juvenile], the court
    shall fix a minimum term of not less than [twenty] years
    nor more than [thirty] years; provided, however, that in
    the case of a sentence of life imprisonment for murder in
    the first degree with extreme atrocity or cruelty committed
    by a [juvenile], the court shall fix a minimum term of
    [thirty] years; and provided further, that in the case of a
    sentence of life imprisonment for murder in the first
    degree with deliberately premeditated malice aforethought
    committed by a [juvenile], the court shall fix a minimum
    term of not less than [twenty-five] years nor more than
    [thirty] years."

    However, the defendant in this case was sentenced to life

without the possibility of parole pursuant to G. L. c. 265,

§ 2 (a), prior to the enactment of the aforementioned

legislative changes in 2014, post-Diatchenko I.   Therefore, this

defendant and other emerging adults sentenced to life without

the possibility of parole prior to July 25, 2014, may only be

resentenced to the constitutionally permissible penalty

available at that time -- life with the possibility of parole

after fifteen years.   See Commonwealth v. Costa, 472 Mass. 139,

146 (2015) (resentencing limited to available statutory penalty

in effect at time of conviction).

    By providing an opportunity for parole, we do not diminish

the severity of the crime of murder in the first degree because
                                                                   37

it was committed by an emerging adult.    Likewise, our decision

today "should not be construed" to suggest that emerging adults

receiving the benefit of resentencing under today's holding

"should be paroled once they have served a statutorily

designated portion of their sentences."   Diatchenko I, 466 Mass.

at 674.   However, as we stated in Diatchenko I, we must

recognize the "unique characteristics" of emerging adults that

render them "constitutionally different" from adults for

purposes of sentencing.   Id., citing Miller, 567 U.S. at 471.

As such, they must be granted a "meaningful opportunity to

obtain release based on demonstrated maturity and

rehabilitation" before the Massachusetts parole board, who will

"evaluate the circumstances surrounding the commission of the

crime, including the age of the offender, together with all

relevant information pertaining to the offender's character and

actions during the intervening years since conviction."

Diatchenko I, supra, quoting Graham, 560 U.S. at 75.

    Conclusion.   We remand this matter to the Superior Court

for resentencing consistent with this opinion.

                                    So ordered.
    KAFKER, J. (concurring).    I concur with the court's

comprehensive review of the expert testimony, the judge's fact

finding, and the applicable law.   I write separately to

emphasize in particular that the letter and spirit of our

trailblazing decision in Diatchenko v. District Attorney for the

Suffolk Dist., 466 Mass. 655, 669 (2013) (Diatchenko I), S.C.,

471 Mass. 12 (2015) (Diatchenko II), directs us to reach the

same conclusion today that we reached a decade ago and extend

those very same protections to the age group at issue --

eighteen through twenty year olds.

    In our landmark decision in Diatchenko I, we relied on the

best science available at the time, legislative recognition of

the legal differences between juveniles and adults in other

contexts, and the special protections of art. 26 of the

Massachusetts Declaration of Rights to declare that the

Legislature's imposition of life sentences without the

possibility of parole for juveniles was unconstitutional,

because juveniles are less culpable than adults and more capable

of change.   We also employed distinctive reasoning that I

discuss in some detail infra.   In so doing, we provided greater

protections for juveniles under art. 26 than the United States

Supreme Court had under the Eighth Amendment to the United

States Constitution, precluding not only mandatory life

sentences without the possibility of parole but also
                                                                   2

discretionary sentences of life without the possibility of

parole.

     In the instant case, we are presented with comprehensive

fact finding evaluating further advancements in developmental

cognitive neuroscience and developmental psychology,1

demonstrating that eighteen through twenty year olds share the

same characteristics that distinguished juveniles from adults in

Diatchenko I and that rendered them less culpable and more

capable of change.   The extensive briefing also demonstrates

legislative recognition that eighteen through twenty year olds

similarly require differential treatment from those twenty-one

and older in other relevant and related contexts.   Indeed, when

this age group has been recognized by the Legislature to require

differential treatment, the legal rights in question implicate

those same distinctive characteristics.

     Due to this convergence of science and law, I conclude that

art. 26 precludes both mandatory and discretionary life

     1 As one of the experts testified, the fields of
developmental cognitive neuroscience and developmental
psychology work in tandem with one another. "Cognitive
neuroscience is the study of the brain and the cognitive
operations . . . the brain supports, including thinking and
decision-making," or "higher cognitive tasks or operation[s],"
while the "developmental component" refers "to the study of the
brain as it develops over time and across the lifespan."
Comparatively, "developmental . . . psychology is concerned with
behavior," and often "the research studies that are conducted in
developmental neuroscience are first informed by behaviors that
are observed in studies of development[al] psychology."
                                                                      3

sentences without the possibility of parole for those who are

older than eighteen but younger than twenty-one at the time they

committed murder in the first degree.    Thus, after serving from

twenty-five to thirty years in prison as now prescribed by the

Legislature for juvenile murderers, these eighteen through

twenty year olds likewise shall have the possibility of

convincing the parole board that they have redeemed themselves

in prison, have taken responsibility for the terrible deaths

that they caused in their youth, and deserve to be paroled.2

     1.   Discussion.   a.   Diatchenko, differentiating

characteristics, and State constitutional law.     Our reasoning in

Diatchenko I built on the foundation of the United States

Supreme Court's Eighth Amendment analysis in Miller v. Alabama,

567 U.S. 460 (2012), particularly "three significant

characteristics differentiating juveniles from adult offenders."

Diatchenko I, 466 Mass. at 660.

     "First, children demonstrate a lack of maturity and an
     underdeveloped sense of responsibility, leading to
     recklessness, impulsivity, and heedless risk-taking.
     Second, children are more vulnerable to negative influences
     and outside pressures, including from their family and
     peers . . . . Finally, a child's character is not as well
     formed as an adult's; his traits are less fixed and his

     2 I note that the defendant here was convicted prior to the
passage of the 2014 legislation that required from twenty-five
to thirty years before parole eligibility, and thus is eligible
for consideration for parole, as this court explained in
Diatchenko I, after fifteen years in prison. See Diatchenko I,
466 Mass. at 673-674 (explaining reasons for fifteen year parole
eligibility date at time).
                                                                    4

      actions less likely to be evidence of irretrievable
      depravity." (Quotations, citations, and alterations
      omitted.)

Id.   Together, these characteristics demonstrated that juveniles

possessed "diminished culpability" and a "heightened capacity

for change."   Cf. id. at 661, quoting Miller, supra at 479.

Recognizing these differences and "[a]n ever-growing body of

research in developmental psychology and neuroscience [that]

continues to confirm and strengthen the Court's conclusions,"

Miller, supra at 472 n.5, the Supreme Court concluded that a

mandatory imposition of a sentence of life without the

possibility of parole for juveniles was cruel and unusual in

violation of the Eighth Amendment, id. at 479.   The Court did,

however, allow a discretionary imposition of this sentence based

on an individualized hearing, requiring judges to consider "how

children are different, and how those differences counsel

against irrevocably sentencing them to a lifetime in prison."

Id. at 480.

      We then took a significant additional step in Diatchenko I,

466 Mass. at 670-671, and went well beyond the Supreme Court's

Eighth Amendment protections, concluding that the greater

protection afforded by art. 26 also prohibited the discretionary

imposition of life without parole for juveniles convicted of

murder in the first degree.   We determined, consistent with the

scientific evidence presented, that "a conclusive showing of
                                                                    5

traits such as an 'irretrievably depraved character,' . . . can

never be made, with integrity, by the Commonwealth at an

individualized hearing to determine whether a sentence of life

without parole should be imposed on a juvenile homicide

offender."   Id. at 669-670, quoting Roper v. Simmons, 543 U.S.

551, 570 (2005).   More specifically, we held that because "the

brain of a juvenile is not fully developed, either structurally

or functionally, by the age of eighteen, a judge cannot find

with confidence that a particular offender, at that point in

time, is irretrievably depraved."   Diatchenko I, supra at 670.

Thus, we concluded that our State Constitution prohibited trial

judges from attempting to make individualized findings that were

impossible to make reliably at the time of sentencing, and so we

imposed a categorical ban on the imposition of this sentence for

juveniles.   Id. at 669-670.

    As the Superior Court judge comprehensively found and as

the court explains in its opinion, the scientific evidence here

demonstrates that the same three characteristics that

distinguished juveniles from adults in Diatchenko I, 466 Mass.

at 669-670, distinguish eighteen through twenty year olds in

essentially the same way.   No one disputes those findings or the
                                                                   6

science on which they are based, including the authors of the

dissenting opinions written in the instant case.3

     I therefore emphasize that, based on the fact findings

here, we cannot distinguish in any way this case from Diatchenko

I on scientific grounds.   That science was also, as explained

ante, a significant factor in the decision in Diatchenko I, 466

Mass. at 669-670, helping to convince this court to provide

greater protection under the State Constitution than the Supreme

Court provided under the Federal Constitution when the Supreme

Court's allowance of discretionary life without parole sentences

for juveniles who committed murder in the first degree could not

be reconciled with the science.   Evolving science helps inform

evolving standards of decency.    Cf. Helling v. McKinney, 509

U.S. 25, 36 (1993) (regarding prison conditions, Eighth

Amendment analysis requires both "scientific and statistical

inquiry into the seriousness of the potential harm" and

"assess[ment] whether society considers the risk . . . to be so

     3 On remand, the judge heard expert testimony and oral
argument and accepted an additional exhibit in evidence, before
issuing findings of fact and conclusions of law on whether
mandatory life without parole sentences for eighteen through
twenty year old offenders violates art. 26. Neither party
disputes his factual findings. Among those findings, the judge
clarified that his findings were limited to those up to age
twenty-one because, while one expert, Dr. Adriana Galván,
included twenty-one year olds in her developmental cognitive
neuroscience research, another expert, Dr. Laurence Steinberg,
did not include them in his developmental psychology research.
                                                                    7

grave that it violates contemporary standards of decency").    We

particularly were concerned that trial judges would be required

to make findings that the science demonstrated were not

possible.   Diatchenko I, supra.   See the amicus brief submitted

by twenty-three retired Massachusetts judges and others, at 36-

40.4

       The Supreme Court has, over the vigorous dissent of the
       4

author of Miller and two other Justices, since held that, for
the individualized hearings required by the Eighth Amendment, "a
finding of fact regarding a child's incorrigibility is not
required" (quotation, citation, and alteration omitted). Jones
v. Mississippi, 141 S. Ct. 1307, 1314-1315 (2021), quoting
Montgomery v. Louisiana, 577 U.S. 190, 211 (2016). That the
Supreme Court does not now require an explicit finding on
incorrigibility under its line of Eighth Amendment cases does
not change our previous determination under art. 26 that such a
finding is necessary to justify a sentence of life without
parole for those under eighteen because our State constitutional
protections are greater than those of the Eighth Amendment. See
Diatchenko I, 466 Mass. at 670.

     Nor is our determination in Diatchenko I inconsistent with
our decision in Commonwealth v. Perez, 477 Mass. 677, 679 (2017)
(Perez I), S.C., 480 Mass. 562 (2018) (Perez II), which required
an individualized hearing "where a juvenile is sentenced for a
nonmurder offense or offenses and the aggregate time to be
served prior to parole eligibility exceeds that applicable to a
juvenile convicted of murder." That hearing is different from
the individualized hearing that we concluded was not possible in
Diatchenko I, 466 Mass. at 669-670, because the hearing required
by Perez I does not concern whether parole eligibility is
necessary, as all juvenile offenders are entitled to parole
eligibility after Diatchenko I. See Perez II, supra at 569.
Rather, it asks judges to consider the permissibility of a
longer term of imprisonment prior to parole eligibility for
nonmurder offenses than for murder in the first degree. See
Perez I, supra; Perez II, supra. Our decision in Perez I, supra
at 686, also established a presumption against such longer
parole eligibility sentences under art. 26 and therefore set a
                                                                      8

    Other important aspects of Diatchenko I also should apply

equally here.   We emphasized, for example, that life sentences

without the possibility of parole were deemed particularly

severe for those required to stay in prison from youth to death;

indeed, we went so far as to compare such sentences to the death

penalty, which we already had deemed "unconstitutional under

art. 26."   See Diatchenko I, 466 Mass. at 670 (describing life

sentences without possibility of parole for juveniles as being

"strikingly similar" to death penalty).    That same reasoning

applies to eighteen through twenty year olds, who likewise are

fated to spend the vast majority of their lives in prison with

no hope of release at any time.     If this case is to be

distinguished from Diatchenko I, it must therefore be on other

grounds, each of which I address and reject infra, turning once

again to Diatchenko I for guidance.

    b.   The Legislature's right to define the punishment for

the crime and distinguish juveniles from adult offenders.

Justices Lowy and Cypher in their dissents emphasize that great

deference is owed to the Legislature's right to define the

punishment for criminal behavior and define the line between

juvenile and adult offenders.     See post at    ,     (Lowy, J.,

dissenting); post at      (Cypher, J., dissenting).    As a general

very high bar to justify them, which we confirmed and clarified
in Perez II, supra at 571-573.
                                                                       9

principle, I wholeheartedly agree with these propositions.       But

in Diatchenko I, we did not defer to the punishment established

by the Legislature or to the line drawing (or, in that case, the

absence of line drawing) between juveniles and adults.     Rather,

we concluded that the punishment, without necessary line

drawing, was unconstitutional.    Diatchenko I, 466 Mass. at 658-

659.    In sum, we did not defer to the Legislature; we concluded

that it acted unconstitutionally.

       Unlike the Supreme Court in its line of cases regarding

acceptable criminal punishments for juveniles under the Eighth

Amendment, we also did not define explicitly a fixed

constitutional line for life sentences without the possibility

of parole when we decided Diatchenko I.    Compare Roper, 543 U.S.

at 574 ("The age of [eighteen] is the point where society draws

the line for many purposes between childhood and adulthood.       It

is, we conclude, the age at which the line for death eligibility

ought to rest" [emphasis added]), with Diatchenko I, 466 Mass.

at 669-670 (relying on "current scientific research on

adolescent brain development" to reach conclusion that "the

judge cannot ascertain, with any reasonable degree of certainty,

whether imposition of this most severe punishment is

warranted").   In defining that line previously in the death

penalty context, the Supreme Court also recognized that it had

itself recently set that line at sixteen and then moved it.
                                                                   10

Roper, supra at 561-562.     Perhaps recognizing that this line was

not fixed for all purposes and might too be a moving target for

sentences of life without the possibility of parole, we did not

attempt such analysis or decide that it was applicable

regardless of the science.    Instead, we only answered what we

were asked:   whether it was constitutional to sentence

"juveniles" to life without the possibility of parole as the

Legislature provided, and we concluded that it was not, because

the science demonstrated that juveniles were less culpable and

capable of change.   Diatchenko I, supra at 671.    We then

referenced and relied on a statutory definition of "juvenile" to

define the scope of our holding at the time.     Id. at 659 n.8,

673 n.17.5

     The question then becomes whether there is a meaningful

constitutional difference between overruling the Legislature's

decision that it is permissible to sentence juveniles to life in

prison without the possibility of parole and overruling the

Legislature's decision that it is permissible to sentence

eighteen through twenty year olds to life in prison without the

possibility of parole, when the fact finding regarding the

     5 I do not in any way seek to redefine eighteen through
twenty year olds as juveniles. Rather, I consider eighteen
through twenty year olds as a distinct legal category as
explained infra, as the Legislature itself has done in a variety
of contexts.
                                                                     11

scientific evidence now conclusively demonstrates that eighteen

through twenty year olds, just like juveniles, are less culpable

for their crimes and more capable of change than adults.

     Justices Lowy and Cypher find such a basis in deference to

the Legislature:    we should defer to the Legislature because it

did not exclude eighteen to twenty year olds from a statute that

provides for life sentences without the possibility of parole

for murder in the first degree.      See post at    ,      (Lowy, J.,

dissenting); post at         (Cypher, J., dissenting).   The same,

however, was true for juveniles when we decided Diatchenko I,

466 Mass. at 672-673.      Although the Legislature at that time

authorized life sentences without the possibility of parole for

juveniles, as explained supra, we found such punishment

unconstitutional.    Id.

     Justices Lowy and Cypher in their dissents also state that

we should defer to the Legislature because it has defined

eighteen as a fixed line between juveniles and adults.6      I

     6 Justice Cypher posits that the extension of rights to
those over the age of eighteen has always been granted first by
the Legislature and not the courts, and so we would be the first
to define protections for a certain category of individuals
based on an age group of our definition. Post at      (Cypher,
J., dissenting). The latter consideration ignores, however, the
evolution of Federal juvenile death penalty jurisprudence, which
involved judicial line drawing based on age without reliance on
a clearly legislatively defined age group. In Thompson v.
Oklahoma, 487 U.S. 815, 823, 838 (1988), a plurality of the
Supreme Court prohibited the imposition of the death penalty for
those under the age of sixteen at the time they committed their
                                                                  12

conclude, as does the court, that the legislative line drawing

is more nuanced.   The Legislature does not uniformly provide

eighteen through twenty year olds with the full benefits and

responsibilities of those twenty-one and older.   Rather, the

Legislature recognizes that eighteen, nineteen, and twenty year

olds fall into a distinct category requiring special

consideration; they are permitted certain legal rights but not

others.   See State House News Service (Sen. Sess.), June 28,

2018 (statement of Sen. Jason Lewis, chair of Joint Committee on

Public Health) (regarding tobacco purchasing age limit, "there

really is no single age of adulthood in our society"; [w]e make

decision[s] on a case-by-case basis depending on the activity").

For example, they are entitled to vote, serve on a jury or in

the military, and drive a car.   See G. L. c. 51, § 1 (voting);

G. L. c. 234A, § 4 (jury); G. L. c. 90, § 8 (driving).   See also

Requirements to enlist in the U.S. military, USA.gov,

offense. This decision stood in contrast to the many ways in
which the age of eighteen stood as a demarcation between
juveniles and adults.

     The Court in Thompson, 487 U.S. at 838, had been asked to
"'draw a line' that would prohibit the execution of any person
who was under the age of [eighteen] at the time of the offense."
The Court limited its decision, however, to "the case before" it
and so drew the line at sixteen. In 2005, in Roper, 543 U.S. at
570-571, the Court took the opportunity to extend Thompson to
protect all juveniles -- those up to age eighteen -- from the
imposition of the death penalty. In both instances, the
judiciary -- not the Legislature -- extended these protections.
For us to do the same would not, therefore, be unprecedented.
                                                                   13

https://www.usa.gov/military-requirements

[https://perma.cc/Y9MG-HWG4] (beginning at age seventeen).       But

they cannot purchase and sell alcohol or tobacco, serve as a

State police officer, gamble, or even supervise drivers with

learner's permits.   See G. L. c. 138, § 34 (alcohol); G. L.

c. 270, § 6 (tobacco); G. L. c. 31, § 58 (municipal police

officer); G. L. c. 22C, § 10 (State police officer); G. L.

c. 23K, § 43 (gambling); G. L. c. 90, § 8B (learner's permits).

They are also excluded from purchasing marijuana by a ballot

initiative, demonstrating that the public recognizes a similar

distinction.   G. L. c. 94G, § 7 (a).   Their rights regarding

firearms are also more limited than those twenty-one and over.

G. L. c. 140, § 131 (d) (iv) (license to carry large capacity

firearm restricted to those twenty-one and over).

    I thus emphasize that legal rights from which eighteen

through twenty year olds are excluded appear to implicate and

reflect a legislative concern about the very characteristics

that are at issue in this case:   "a lack of maturity and an

underdeveloped sense of responsibility, leading to recklessness,

impulsivity, and heedless risk-taking" and a greater

"vulnerab[ility] . . . to negative influences and outside

pressures, including from their family and peers" (quotations

and citations omitted).   Diatchenko I, 466 Mass. at 660.

Senator Patricia Jehlen, the author of an amendment to the
                                                                     14

expanded gaming bill that prohibited marketing to individuals

under twenty-one, stated:    "The bill itself says that casinos

may not allow people under the age of [twenty-one]. . . .

Current Massachusetts law says you can't buy alcohol if you're

under [twenty-one].    I think that these are consistent that

people's brains have not matured by the time they're

[eighteen]."   State House News Service (Sen. Sess.), Oct. 11,

2011.   Likewise, the legislative history regarding increasing

the age for tobacco consumption to twenty-one shows that the

Legislature was concerned about the underdeveloped brains of

young people, including those above eighteen.     See State House

News Service (Sen. Sess.), June 28, 2018 (statement of Sen.

Jason Lewis) ("Our young people are particularly

susceptible. . . .    [Nicotine] has harmful health impacts on the

developing brain. . . .     It helps [to] get tobacco products out

of high school social networks"); Press Release, Senate Passes

Jason Lewis Bill to Protect Youth from the Health Risks of

Tobacco and Nicotine Addiction (June 30, 2018),

https://senatorjasonlewis.com/2018/06/30/tobacco-21

[https://perma.cc/6MQM-QHXQ] (quoting Sen. President Harriette

L. Chandler, "This legislation protects young adults whose minds

and bodies are still developing . . .").    See also Governor's

Legislative Files, House Bill No. 4218, "An Act increasing the

minimum age for appointment as a police officer," Bill Summary
                                                                  15

(2003) ("Advocates of this legislation suggest increasing the

minimum age for appointment for the position of police officer

will ensure that individuals taking on the responsibilities

associated with modern policing posses[s] the requisite life

skills and maturity").7

     The criminal justice system also reflects special

consideration for this age group, again reflecting the special

characteristics of eighteen through twenty year olds.    For

example, the Legislature has authorized the Department of Youth

Services to maintain custody of young people adjudicated to be

youthful offenders up to age twenty-one.   G. L. c. 119, § 58.

Likewise, the Massachusetts Sentencing Guidelines have

instructed judges to consider the developmental characteristics

of eighteen through twenty year olds even when they have been

tried as adults.   The Legislature has also, in its recent

comprehensive criminal justice reform, authorized the State and

     7 Federal legislative history of the highway funding law
that led Massachusetts to raise the drinking age to twenty-one
discussed similar concerns. See Hearing before Subcommittee on
Surface Transportation of the United States Senate Committee on
Commerce, Science, and Transportation on Oversight of the
National Highway Traffic Safety Administration (Sept. 13, 1983),
reprinted in Legislative History of the Surface Transportation
Assistance Act of 1982 Amendments (1984) (statement of Robert S.
Vinetz, M.D.) (younger drivers' high rate of motor vehicle
accidents due to "especially deadly combination of being new and
inexperienced drivers, of having the tendency toward increased
risk-taking, of having an exaggerated belief in their own
invulnerability and in experimenting with alcohol and drugs").
                                                                  16

county prison systems to "establish young adult correctional

units" with "targeted interventions, age appropriate

programming[,] and a greater degree of individual attention" for

those within this age group and also extended such consideration

to those as old as twenty-four, G. L. c. 127, § 48B.   In sum,

the Legislature has recognized that eighteen through twenty year

olds are a distinct category requiring special consideration, at

least regarding legal rights that implicate risky, impulsive,

and potentially dangerous behavior and peer pressure -- the very

characteristics at issue in this case.

    Given this legislative recognition of the need for

differential treatment of eighteen through twenty year olds in

such contexts, and the science and fact finding in this case,

which equates eighteen through twenty year olds to juveniles on

the relevant three characteristics that rendered juveniles less

culpable for their crimes, more capable of change, and thus

entitled to the possibility of parole in Diatchenko I, 466 Mass.

at 660, I conclude that eighteen through twenty year olds should

likewise be entitled to State constitutional protection from

life sentences without the possibility of parole.   As in

Diatchenko I, we should not defer to the Legislature when it

recognizes the distinctive characteristics of the eighteen

through twenty year old defendants at issue and treats them

differently from those twenty-one and over in many ways, but
                                                                   17

then disregards those differences for our most severe criminal

punishments.   Upholding such sentences means that we disregard

the best science and continue to impose the most severe penalty

on a distinct legal category of individuals that we know are

less culpable and more capable of change.8

     For all these reasons, this court in Diatchenko I, 466

Mass. at 671, declared the statute unconstitutional as applied

to a certain age group.   Deference to the Legislature's

determination of a punishment that we, in Diatchenko, analogized

to the death penalty is different from ordinary deference.    To

determine whether such a punishment is cruel or unusual is a

critical function of this court, and one that the court has

exercised with particular vigilance despite the objections of

dissenting justices calling for greater deference to the

Legislature.   See id. at 672.   See also, e.g., Commonwealth v.

Colon-Cruz, 393 Mass. 150, 181 (1984) (Wilkins, J., dissenting);

     8 I also concur with the court's decision to limit this
relief to those under twenty-one. Unlike eighteen to twenty
year olds, those twenty-one and over have been considered by the
Legislature to have the full benefits and responsibilities of
adults. I consider the Legislature's recognition of the need
for differential treatment of those eighteen to twenty in a
variety of other contexts when the legal rights in question
implicate the same distinctive characteristics at issue in this
case to be an important component of the analysis. That
legislative recognition is absent when we consider those twenty-
one and over. It is the convergence of law and science, not
just science alone, that governs the art. 26 analysis here.
                                                                  18

id. (Nolan, J., dissenting); District Attorney for Suffolk Dist.

v. Watson, 381 Mass. 648, 687 (1980) (Quirico, J., dissenting).9

     c.    The role of the tripartite analysis in Diatchenko I.

Another exceptional aspect of the Diatchenko I decision is the

legal authority to which this court turned for guidance and

support.   We did not expressly employ the tripartite analysis

from Commonwealth v. Jackson, 369 Mass. 904, 910, 913 (1976),

and Cepulonis v. Commonwealth, 384 Mass. 495, 497-498 (1981)

(considering "the penalties prescribed for the same offense in

other jurisdictions"), and therefore tie our decision to how

most other States treated like offenders by applying the third

step of that analysis.   We did not even compare ourselves to

other States or express concern that we were providing greater

protection than those other States.   Again, this is a critical

and distinctive aspect of Diatchenko I.    Instead, relying on our

own State Constitution, a legislatively defined category, which

in that case was juveniles, and comprehensive fact finding

grounded in science, to ensure the objectivity and integrity of

our decision-making process, we broke new ground in this

landmark decision, like other seminal State constitutional

     9 The deference recommended here has similarities to those
dissents. See, e.g., Colon-Cruz, 393 Mass. at 184-185 (Nolan,
J., dissenting). It is important to remember that Diatchenko I,
466 Mass. at 670, made the comparison between life without the
possibility of parole and the death penalty. This is another
critical aspect of Diatchenko I that we cannot ignore.
                                                                    19

decisions we have issued.10    Compare Goodridge v. Department of

Pub. Health, 440 Mass. 309, 312, 339 n.31 (2003) (recognizing

that "our decision marks a change in the history of our marriage

law" while noting only three other States' courts had taken

affirmative steps to recognize same-sex marriage under their

Constitutions while Federal government had not); Watson, 381

Mass. at 650, 662 (striking down death penalty for violating

art. 26 because it was "unacceptably cruel under contemporary

standards of decency" despite lack of "unanimity of public

opinion" as it was "administered with unconstitutional

arbitrariness and discrimination").

     For further support when deciding Diatchenko I, 466 Mass.

at 285 n.16, we turned to the author of our State Constitution,

John Adams, and even widened our perspective internationally.

We noted Adams's reminder that "we belong to an international

community that tinkers toward a more perfect government by

learning from the successes and failures of our own structures

and those of other nations."    Id., citing J. Adams, Preface, A

Defence of the Constitutions of Government of the United States

of America (1797).   We also referenced the United Nations

     10I note that Diatchenko I has been cited in 127 decisions,
including fifty out-of-State cases. See Goldstein, One of One:
Justice Gants and Lessons from the Keo Case, 62 B.C. L. Rev.
2827, 2828 (2021) (referring to Diatchenko I as "momentous
decision[]").
                                                                  20

Convention of the Rights of the Child, which bans life in prison

without parole for juveniles.    Diatchenko I, supra.

    Given the distinct letter and spirit of Diatchenko I

described in detail supra, and the undisputed factual findings

here demonstrating that eighteen through twenty year olds share

the same relevant characteristics regarding diminished

culpability and heightened capacity for change as juveniles, I

conclude that we should extend the very same protections

provided to Gregory Diatchenko to eighteen through twenty year

olds.    I discern no basis for distinguishing them given the

distinct reasoning developed in Diatchenko I.    A sentence of

life in prison without parole eligibility review for those up to

age twenty-one -- individuals with diminished culpability and a

heightened capacity for change -- is no less cruel or unusual

than it is for those up to age eighteen.    Cf. Diatchenko I, 466

Mass. at 670-671.   Thus, we should have been "obliged to declare

part of [this statute] unconstitutional," id. at 672, and have

provided these eighteen through twenty year old homicide

offenders with "a meaningful opportunity for release on parole,"

should they "demonstrate[] maturity and rehabilitation," so that

their "life sentence [is] constitutionally proportionate,"

Diatchenko II, 471 Mass. at 29-30.

    d.    Limited remedy.   We also, as in Diatchenko I, 466 Mass.

at 671, need only hold a very specific application of the
                                                                   21

statute unconstitutional.   As we explained in Diatchenko I, "the

unconstitutionality of this punishment arises not from the

imposition of a sentence of life in prison, but from the

absolute denial of any possibility of parole" for a class of

offenders who a trial judge cannot reliably determine to be

irretrievably depraved at the time of sentencing.     See id.   Once

they have a chance to mature, however, that decision, as well as

the other factors relevant to parole, would and should be made

by a parole board.   That decision would also be made after many

years of imprisonment.   See id. at 674.   Under current law,

those under age eighteen who are convicted of murder in the

first degree are eligible for parole only after serving from

twenty-five to thirty years for murder convicted with deliberate

premeditation and thirty if the murder was committed with

extreme atrocity or cruelty.    G. L. c. 279, § 24.   I would

extend the same opportunity to those older than eighteen but

under the age of twenty-one.   Essentially, the legislative

regime imposed for juvenile murderers would be extended to

eighteen to twenty year olds without further changes in the

statutory scheme.

    The possibility of such reformative change after a lengthy

period of incarceration has also been demonstrated since we

decided Diatchenko I.    Of the juvenile offenders who were

serving mandatory life sentences without parole at the time of
                                                                   22

the Diatchenko I decision and have since received parole

hearings, seventy-four percent have been granted parole.   As

Diatchenko I and its aftermath have demonstrated, the

possibility of redemption exists for the young, even those who

have committed the most horrible crimes, after they have spent

many years in prison maturing and taking responsibility for the

terrible deaths that they caused in their youth.

       For all these reasons, I conclude that a sentence of life

without the possibility of parole for eighteen through twenty

year olds constitutes cruel or unusual punishment under art. 26

of our Declaration of Rights.    That applies to both

discretionary as well as mandatory life sentences without the

possibility of parole for those eighteen through twenty years of

age.
    WENDLANDT, J. (concurring, with whom Gaziano, J., joins).

The determination whether the Commonwealth's harshest punishment

is so disproportionate to the offender as to shock the conscious

is neither one we abdicate to the Legislature, as marshalled by

the dissent, nor one we rest on the shoulders of scientists and

social scientists.   I write to clarify what should be pellucid:

it is our constitutional duty to ensure prescribed punishments

pass constitutional muster, and nothing in art. 30 of the

Massachusetts Declaration of Rights prevents us from doing so.

To be faithful to the enormity of this charge, we must undertake

a comprehensive review of our statutes, the scientific record,

our collective experiences, and common sense.

    Having examined these sources, I conclude that they confirm

what any parent of adult children can tell you:   a child does

not go to bed on the eve of her eighteenth birthday and awaken

characterized by a lessened "transient rashness, proclivity for

risk, and inability to assess consequences."    Miller v. Alabama,

567 U.S. 460, 472 (2012).   In recognition of this indisputable

fact, society does not treat the transition from childhood to

adulthood as a binary act accomplished at age eighteen; becoming

an adult is much more fluid, with development continuing long

after a child's eighteenth birthday.   In the ways that matter

for the Commonwealth's harshest punishment, young adults of the

ages of eighteen, nineteen, and twenty share key characteristics
                                                                   2

with their under-eighteen year old peers; they "have diminished

culpability and greater prospects for reform" than older adults

and "are less deserving of the most severe punishments."     See

id. at 471, quoting Graham v. Florida, 560 U.S. 48, 68 (2010).

For this reason, condemning a person in the process of "growing

up" to die in prison on the basis that she falls on the "wrong"

side of an arbitrary line drawn at age eighteen is inconsistent

with "the evolving standards of decency that mark the progress

of a maturing society" (citation omitted).   Graham, supra at 58.

Accordingly, I agree with the court that imposition of life

without the possibility of parole on young adults ages eighteen,

nineteen, and twenty is unconstitutional.

    1.   Legislature's treatment of young adults.   Undoubtedly,

the first source in the determination of our contemporary

standards of decency that define the bounds of cruel punishment

is legislative enactments.   See Good v. Commissioner of

Correction, 417 Mass. 329, 335 (1994) ("In divining contemporary

standards of decency, we may look to State statutes and

regulations, which reflect the public attitude as to what those

standards are").   See also Graham, 560 U.S. at 61, quoting Roper

v. Simmons, 543 U.S. 551, 563 (2005) ("The Court first considers

'objective indicia of society's standards, as expressed in

legislative enactments and state practice' . . ."); Atkins v.

Virginia, 536 U.S. 304, 312 (2002) ("the clearest and most
                                                                    3

reliable objective evidence of contemporary values is the

legislation enacted by the country's legislatures" [quotation

and citation omitted]).1

     Our statutes reflect legislative recognition that maturity

is a gradual endeavor,2 and that while age eighteen is a

milestone, society does not view it as the end of the

metamorphosis toward adulthood.   As the court and Justice Kafker

thoroughly catalogue, for many activities considered by society

to require greater care, less risk taking, and more resilience

     1 In concluding that a mandatory sentence of life in prison
without the possibility of parole violated the Eighth Amendment
to the United States Constitution when imposed on juvenile
nonhomicide offenders, the United States Supreme Court
considered that, although thirty-seven State legislatures
permitted the sentence, only eleven States imposed the sentence
in practice, and vanishingly few juvenile offenders actually
received it. See Graham, 560 U.S. at 62-67 (only approximately
123 juvenile nonhomicide offenders were serving sentences of
life without parole; seventy-seven of those offenders were in
Florida, and the remainder were in just ten States). See also
Atkins, 536 U.S. at 316 (considering that "even in those States
that allow the execution of [offenders with intellectual
disabilities], the practice is uncommon," in concluding that "a
national consensus has developed" against executing such
individuals). Because the sentence is mandatory for all adults
over the age of eighteen in Massachusetts, see G. L. c. 265,
§ 2 (a), we cannot look to sentencing practices as they pertain
to young adult offenders.

     2 As Justice Cypher notes, post at    , at a point earlier
than the age of eighteen, the Legislature has recognized that
one commences the transition from being a child to being an
adult and therefore awards certain freedoms to these young
people before they turn eighteen years old. For example, young
women, as early as age sixteen, can obtain an abortion without
parental consent. See G. L. c. 112, § 12R.
                                                                   4

to peer pressure, the Legislature continues to treat young

adults over the age of eighteen like juveniles.   To engage in

these activities legally, young adults must wait until they are

twenty-one.

     This special treatment exemplifies the Legislature's

acknowledgment of two facts:   first, that the impetuousness of

youth, the proclivity to risk taking, and the susceptibility to

peer pressure are not attributes exclusive to those under the

age of eighteen, and instead continue into young adulthood; and

second, that these attributes are not fixed, but generally fade

over time because young adults, like juveniles, are

characterized by a malleability of character.3

     2.   Science and social science.   Of course, consideration

of legislation is the beginning; it is not the end of our

analysis under art. 26 of the Massachusetts Declaration of

Rights.   To be faithful to our responsibility to protect

individuals from cruel or unusual punishment meted out by the

     3 Private institutions also recognize that young adults are
not ready for all the responsibilities of adulthood. See, e.g.,
K.U. Lindell & K.L. Goodjoint, Juvenile Law Center, Rethinking
Justice for Emerging Adults: Spotlight on the Great Lakes
Region, at 12 (2020) ("while not a statutory restriction, most
car rental companies limit rentals to individuals under age
[twenty-five], recognizing the increased risk posed by this age
group"). See also Metz, How Age and Gender Affect Car Insurance
Rates, Forbes Advisor (updated Aug. 17, 2023), https://www
.forbes.com/advisor/car-insurance/rates-age-and-gender [https:
//perma.cc/LB8G-PHEG] ("The high car insurance rates that young
drivers pay start to go down at age [twenty-five]").
                                                                     5

State, we cannot be blind to the truths that the scientific

sources with which we have been presented show.4

     Our experiment with scientific fact finding on the topic of

adult brain development validates the graduated treatment of

young persons reflected in our statutes.    The court's careful

review of this record is undisputed.   In brief, it shows that

neuroscientists see in their magnetic resonance imaging (MRI)

scans corroboration for that which we experience in life; the

brain characteristics of persons even years older than eighteen

mirror those of persons under eighteen.    The brain generally

continues to develop through the mid-twenties.     Until some ill-

defined point in the third decade of life, adults, especially

     4 See, e.g., Miller, 567 U.S. at 471 (determination that
life in prison without possibility of parole for juveniles
violates Eighth Amendment rested "not only on common sense -- on
what 'any parent knows' -- but on science and social science as
well" [citation omitted]); Graham, 560 U.S. at 68 (considering
"developments in psychology and brain science" in Eighth
Amendment proportionality analysis as to life in prison without
possibility of parole for juveniles convicted of nonhomicide
offenses); Roper v. Simmons, 543 U.S. 551, 569 (2005)
(considering what "any parent knows" and what "scientific and
sociological studies . . . tend to confirm" to conclude death
penalty for juveniles violates Eighth Amendment); Diatchenko v.
District Attorney for the Suffolk Dist., 466 Mass. 655, 669
(2013), S.C., 471 Mass. 12 (2015) (concluding imposition of
sentence of life in prison without possibility of parole for
juveniles, even after individualized hearing, violates art. 26
of Massachusetts Declaration of Rights "[g]iven current
scientific research on adolescent brain development").
                                                                      6

men,5 generally are more impulsive and their brains are more

plastic than those of older adults.6

     3.    Collective experience and common sense.   Significantly,

while the findings based on current technological advances in

brain science show substantial similarities between juveniles

and young adults, we do not check our common sense at the

laboratory door.   Our statutes, experiences, and common sense

tell us that there is no magic switch to the process of growing

up, and that fact, now buttressed by neuroscientific data and

informed by social science studies, must be weighed in the

exercise of our duty to determine whether punishment is cruel or

unusual.    See Matter of the Personal Restraint of Monschke, 197

Wash. 2d 305, 306 (2021) ("Modern social science, our precedent,

     5 See L. Brizendine, The Female Brain 44 (2006) (finding
that female brain "matures two or three years earlier than the
male brain"). See also Cauffman & Steinberg, (Im)maturity of
Judgment in Adolescence: Why Adolescents May Be Less Culpable
Than Adults, 18 Behav. Sci. & L. 741, 753 (2000) (finding that
"females exhibit greater psychosocial maturity than males").

     6 Scientific studies report brain maturation at different
ages: sometimes at the age of twenty-one, sometimes at twenty-
two, sometimes at twenty-three or twenty-five, and sometimes in
the middle to late twenties. Moreover, studies report that
certain aspects of brain development, such as susceptibility to
peer pressure and impulse control, also appear to mature at
different rates.
                                                                   7

and a long history of arbitrary line drawing have all shown that

no clear line exists between childhood and adulthood").7

     The scientific snapshot in this case confirms that which is

apparent in our laws and in our treatment of this age cohort

more generally –- namely, that in the ways that matter for

criminal sentencing, young adults are similar to juveniles.

Like juveniles, young adults have "an underdeveloped sense of

responsibility, leading to recklessness, impulsivity, and

heedless risk-taking"; they are more vulnerable to peer

pressure; and their "character is not as well formed as an

adult's . . . and [their] actions [are] less likely to be

evidence of irretrievabl[e] deprav[ity]" (quotations omitted).

Diatchenko v. District Attorney for the Suffolk Dist., 466 Mass.

     7 The parties in this case ask us to consider the
constitutionality of the punishment of life in prison without
the possibility of parole when it is imposed on defendants aged
eighteen, nineteen, and twenty. That the scientific record is
not precise as to where the line should be drawn, see note 6,
supra, should come as no surprise given our collective
experiences showing that, while some generalizations may be
drawn, in the end "growing up" is an individualized endeavor.
This does not mean that "we may as well give up and let the
[L]egislature draw its arbitrary lines." Matter of the Personal
Restraint of Monschke, 197 Wash. 2d at 323. At the least, in
response to the only question with which we have been presented
in this case, I conclude that drawing a fixed line at the age of
eighteen, thereby leaving young adults aged eighteen, nineteen,
and twenty to the punishment, is not supported by our statutes,
the scientific data and social science, our collective
experiences, or common sense.
                                                                      8

655, 660 (2013) (Diatchenko I), S.C., 471 Mass. 12 (2015),

quoting Miller, 567 U.S. at 471.

    Relying on these hallmarks of youth, the United States

Supreme Court concluded that mandatory life in prison without

the possibility of parole is a cruel punishment when applied to

juveniles.   Miller, 567 U.S. at 489.   And, in view of these

characteristics of juveniles, we separately concluded that art.

26 prohibits the mandatory imposition of this punishment.       See

Diatchenko I, 466 Mass. at 667.    We also concluded that art. 26

offers greater protections to our children than are available

under the Eighth Amendment to the United States Constitution.

Specifically, we concluded that, in view of the hallmarks of

youth that characterize juveniles, art. 26's greater protection

prohibits so-called Miller hearings to determine whether, on an

individualized consideration of a particular juvenile homicide

defendant's circumstances, the sentence of life without the

possibility of parole was proportionate.    Id. at 669-671.

Because the aforementioned review of our statutes, the

scientific data, collective experiences, and common sense

confirms that these same qualities characterize young adults, it

necessarily follows that art. 26 prohibits the punishment as

applied to this cohort.   For these reasons, I concur.
    LOWY, J. (dissenting, with whom Cypher and Georges, JJ.,

join).   I cannot say that society, through its elected

officials, may not express its revulsion of the crime of murder

in the first degree by imposing a punishment of life without the

possibility of parole on adults without offending our

Declaration of Rights.   Therefore, I respectfully dissent.

    The power to "define a crime and ordain its punishment" is

an exclusively legislative function, and "in judging legislative

determinations of crimes and punishments, we exercise our powers

of review with great caution" (citation omitted).     Opinions of

the Justices, 378 Mass. 822, 830 & n.7 (1979).   For the crime of

murder in the first degree, the Legislature has deemed the

mandatory imposition of life without the possibility of parole

to be the appropriate punishment for adults eighteen and older

convicted of this offense.   While we have an obligation to

intervene when the Legislature acts unconstitutionally, unless

the punishment the Legislature imposes is "so disproportionate"

that it "shocks the conscience and offends fundamental notions

of human dignity" (citation omitted), Cepulonis v. Commonwealth,

384 Mass. 495, 497 (1981), we must exercise restraint and uphold

it, see art. 26 of the Massachusetts Declaration of Rights;

Eighth Amendment to the United States Constitution.

    In this case, the defendant argues that, in light of recent

advances in scientific brain research concerning young adults,
                                                                       2

the line between those who may constitutionally be subject to

the mandatory imposition of life without the possibility of

parole and those who may not should be at the age of twenty-one,

rather than at the age of eighteen.    Our analysis for

determining whether a punishment is constitutionally

disproportionate considers whether the punishment is cruel or

unusual in light of "contemporary standard[s] of decency"

(citation omitted).    Libby v. Commissioner of Correction, 385

Mass. 421, 431 (1982).    We look to statutes enacted by the

Legislature, along with regulations, as the best objective

evidence for divining contemporary values.    See Good v.

Commissioner of Correction, 417 Mass. 329, 335 (1994).      Doing so

is not affording uncritical deference to the Legislature's

choice of punishment, but rather it is a direct application of

our constitutional doctrine that looks to legislation to derive

contemporary values.     Indeed, "legislatures, not courts, are

constituted to respond to the will and consequently the moral

values of the people."    See Gregg v. Georgia, 428 U.S. 153, 175

(1976), quoting Furman v. Georgia, 408 U.S. 238, 383 (1972)

(Burger, C.J., dissenting).    Consequently, to determine whether

this mandatory sentence violates art. 26, we must look to

legislative evidence to determine whether the line that the

defendant urges us to draw at the age of twenty-one is one that

is consistent with society's contemporary values.
                                                                    3

    Contrary to the court's conclusion that it is, the

objective sources of contemporary standards of decency in the

Commonwealth simply do not reflect a public consensus that life

without parole, when imposed mandatorily on individuals from

eighteen to twenty who have been convicted of murder in the

first degree, is cruel or unusual.   Rather, the Legislature has

definitively drawn the line between childhood and adulthood at

eighteen, and objective indicia of contemporary standards of

decency in the Commonwealth demonstrate support for, rather than

objection to, treating individuals within this age range as

adults in our criminal justice system when they commit the crime

of murder in the first degree.

    Where individuals from eighteen to twenty-one have been

deemed adults by the Legislature and society, precedent relating

to the sentencing of juveniles -- who are "constitutionally

different from adults for purposes of sentencing" -- is inapt.

Miller v. Alabama, 567 U.S. 460, 471 (2012).   Thus, our decision

in Diatchenko v. District Attorney for the Suffolk Dist., 466

Mass. 655, 669 (2013) (Diatchenko I), S.C., 471 Mass. 12 (2015),

cannot resolve the question of the proportionality of the

mandatory sentence challenged in this case.    In Diatchenko I, we

did not purport to draw a line between juveniles and adults.

Our focus, rather, was on a category of individuals --

predefined by the Legislature -- and our inquiry as to that
                                                                      4

category was precise and limited.    See id. at 659 n.8.   Where

the United States Supreme Court concluded in Miller, supra at

469, that imposing mandatory life without parole on juveniles

violates the Eighth Amendment, we were addressing only the

discretionary imposition of such a sentence, i.e., whether,

under art. 26, an individualized assessment of a juvenile

offender could ever result in a determination that "a sentence

of life without parole should be imposed on a juvenile homicide

offender."    Diatchenko I, supra at 670.   We concluded that art.

26 did not permit such an individualized assessment at the time

of sentencing.

    As it relates to the court's conclusion that this mandatory

sentence is categorically unconstitutional, scientific brain

research, untethered to societal views expressed through

legislation, can neither draw the line between childhood and

adulthood nor manufacture a new category of individuals entitled

to distinct constitutional treatment for purposes of determining

whether a sentence is constitutionally disproportionate under

art. 26.     And, even if it could, science does not definitively

place the line of brain maturation at twenty-one, but rather

suggests that it extends into the mid-twenties.     Perhaps nothing

speaks louder to the flaws in the court's holding that this

mandatory sentence violates art. 26 than the court having

crafted a line that ends at age twenty-one, thereby engaging in
                                                                   5

legislative line drawing inconsistent with the science upon

which it relies.   Where punishment is involved, we must look to

society and the Legislature to determine where the appropriate

line is and where it should be.

    Our assessment under art. 26 is not whether the mandatory

imposition of life without the possibility of parole for

individuals from eighteen to twenty-one is, in our view, wise,

prudent, or even best for society.     Our inquiry is limited to

whether the punishment, chosen by the Legislature, is so

disproportionate that it reaches the level of cruel or unusual.

See Diatchenko I, 466 Mass. at 669.    Because, under our

contemporary standards of decency and precedent, the mandatory

imposition of life without the possibility of parole on adults

who commit murder in the first degree when they are from

eighteen to twenty-one is not "so disproportionate" that "it

'shocks the conscience and offends fundamental notions of human

dignity,'" id., quoting Cepulonis, 384 Mass. at 497, the

sentence does not violate art. 26's proscription against cruel

or unusual punishment.    It therefore must be upheld.

    Background.    On September 25, 2011, fourteen year old

Kimoni Elliott was visiting his schoolmate and friend, Jaivon

Blake, who lived in the area of Geneva Avenue and Everton Street

in the Dorchester section of Boston.    Elliott lived on Everton

Street in Dorchester.    That afternoon, Elliott was standing
                                                                       6

outside a convenience store on Geneva Avenue near Levant Street

in Dorchester, an area controlled by the "Flatline" gang.

Elliott was looking for somebody old enough to purchase rolling

papers for marijuana cigarettes for him.     The defendant,

eighteen year old Sheldon Mattis, was a member of the Flatline

gang.   He had been playing football on Levant Street with some

other people when he observed Elliott walking toward the

convenience store.   The defendant approached Elliott and offered

to purchase rolling papers for him, and after doing so, the

defendant asked Elliott where he was from.    When Elliott

responded, "Everton," the defendant assumed that Elliott was a

member of a rival gang.

    Elliott and Blake then met in a nearby parking lot and

started walking up Geneva Avenue towards Blake's home while the

defendant returned quickly towards Levant Street.     Minutes

later, the defendant met with seventeen year old Nyasani Watt on

the corner of Levant Street and Geneva Avenue.    He turned his

bicycle over to Watt and handed Watt his gun.     The defendant

then pointed out Elliott and Blake to Watt, patted him on the

back, and told him that Watt "needed to go handle that."        Watt

complied.   Watt approached the victims from behind while on the

bicycle and fired multiple shots at them.     Blake fell to the

ground and later died from his injuries.     Elliott, despite being

shot in the neck and arm, survived.
                                                                       7

    Discussion.     1.    Judicial review of punishment designated

by the Legislature.      "[T]he power of punishment is vested in the

legislative, not in the judicial department.      It is the

[L]egislature, not the [c]ourt, which is to define a crime and

ordain its punishment."      Opinions of the Justices, 378 Mass. at

830 n.7, quoting United States v. Wiltberger, 18 U.S. (5 Wheat.)

76, 95 (1820).    Entrusted with this authority, "[t]he

Legislature has great latitude to determine what conduct should

be regarded as criminal and to prescribe penalties to vindicate

the legitimate interests of society."      Commonwealth v. Jackson,

369 Mass. 904, 909 (1976).      The Legislature's judgment in this

area is thus "to be accorded due respect," Opinions of the

Justices, supra at 830, and it is subject only to the

constitutional limitations imposed by the Eighth Amendment and

art. 26, see Jackson, supra.

    Article 26, which affords greater protections than the

Eighth Amendment, proscribes cruel or unusual punishment; the

"touchstone" of this proscription is proportionality.

Commonwealth v. Yat Fung Ng, 491 Mass. 247, 271 (2021).       This

"flows from the basic 'precept of justice that punishment for

crime should be graduated and proportioned' to both the offender

and the offense."     Diatchenko I, 466 Mass. at 669, quoting

Miller, 567 U.S. at 469.      Our role as the judiciary is therefore

to determine whether the punishment designated by the
                                                                           8

Legislature is "so disproportionate to the offense as to

constitute cruel [or] unusual punishment."1      Cepulonis, 384 Mass.

at 496.

       "To reach the level of cruel [or] unusual, the punishment

must be so disproportionate to the crime that it 'shocks the

conscience and offends fundamental notions of human dignity.'"

Diatchenko I, 466 Mass. at 669, quoting Cepulonis, 384 Mass. at

497.       In conducting this analysis, we consider "contemporary

standards of decency which mark the progress of society."

Diatchenko I, supra, quoting Good v. Commissioner of Correction,

417 Mass. 329, 335 (1994).       "But in judging legislative

determinations of crimes and punishments, we exercise our powers

of review with great caution."       Opinions of the Justices, 378

Mass. at 830.       See Jackson, 369 Mass. at 909 ("It is thus with

restraint that we exercise our power of review to determine

whether the punishment before us exceeds the constitutional

limitations imposed by the Eighth Amendment and by art. 26").

       "Therefore, in assessing a punishment selected by a

democratically elected [L]egislature against the constitutional

measure, we presume its validity."       Gregg, 428 U.S. at 175.     See

Jackson, 369 Mass. at 909, quoting Weems v. United States, 217

       Article 26 prohibits the infliction of "cruel or unusual
       1

punishments," while the Eighth Amendment proscribes "cruel and
unusual punishments."
                                                                      9

U.S. 349, 379 (1910) ("The function of the [L]egislature is

primary, its exercises fortified by presumptions of right and

legality, and is not to be interfered with lightly, nor by any

judicial conception of their wisdom or propriety").     "[W]hile we

have an obligation to insure that constitutional bounds are not

overreached, we may not act as judges as we might as

legislators."   Gregg, supra at 174-175.    "We may not require the

[L]egislature to select the least severe penalty possible so

long as the penalty selected is not cruelly inhumane or

disproportionate to the crime involved.    And a heavy burden

rests on those who would attack the judgment of the

representatives of the people."     Id. at 175.   Accordingly, "a

heavy burden is on the sentenced defendant to establish that the

punishment is disproportionate to the offense for which he was

convicted."   Commonwealth v. Bianco, 390 Mass. 254, 260-261

(1983), quoting Commonwealth v. O'Neal, 369 Mass. 242, 248

(1975) (Tauro, C.J., concurring).

     In concluding that the mandatory imposition of life

imprisonment without the possibility of parole for individuals

from eighteen to twenty-one who have been convicted of murder in

the first degree violates art. 26, the court considers

contemporary standards of decency and prior precedent.     See ante

at   .   Rather than consider science as an independent factor

in assessing proportionality, the court, for the first time,
                                                                   10

concludes that "current scientific consensus regarding the

characteristics of the class can help determine the contemporary

standards of decency pertaining to that class."   Id. at      .

The incorporation of science -– with which I agree -– into the

consideration of contemporary standards of decency in the

constitutional analysis of art. 26 risks diluting the value of

both science and contemporary standards of decency in analyzing

proportionality.   To understand contemporary standards of

decency, we must look to "'objective indicia of society's

standards, as expressed in legislative enactments and state

practice[,]' to determine whether there is a national consensus

against the sentencing practice at issue." Graham v. Florida,

560 U.S. 48, 61 (2010), quoting Roper v. Simmons, 543 U.S. 551,

552 (2005).   Science, no doubt, is a valuable source in

considering proportionality, as well as in assisting

legislatures in how best to line draw around sentencing.

    But science and contemporary standards of decency, although

both vitally important, are distinct sources of information.      It

is necessary to independently examine how elected officials and

States have chosen to express consensus on the proportionality

of punishment, themselves having had the opportunity to weigh

myriad factors, including scientific development, in their

decision-making processes.   The judge's factual findings in July

2022 as to the brain development of emerging adults were well
                                                                  11

supported, and indeed I embrace them.    But the court's

incorporation of science into contemporary standards of decency

does not change the outcome of this case.    Nothing about

mandatory life imprisonment without the possibility of parole

for individuals from eighteen to twenty-one who have been

convicted of the most heinous crime of murder in the first

degree -- either with deliberate premeditation, with extreme

atrocity or cruelty, or with actual malice in the commission or

attempted commission of a crime punishable with life

imprisonment -- offends contemporary standards of decency.     See

Commonwealth v. Okoro, 471 Mass. 51, 61 (2015) ("art. 26

nevertheless 'draw[s] its meaning from the evolving standards of

decency that mark the progress of a maturing society,' such that

developments in the area of juvenile justice in judicial

opinions and legislative actions at the State, Federal, and

international levels help to inform our understanding of what

art. 26 protects" [citation omitted]).

    Accordingly, I address contemporary standards of decency,

precedent, and science in turn.

    2.   Contemporary standards of decency.    "Article 26 bars

punishments which are found to be cruel or unusual in light of

contemporary standards of decency which mark the progress of

society."   Good, 417 Mass. at 335.   The evaluation of

contemporary standards of decency to assess disproportionality
                                                                   12

"should be informed by 'objective factors to the maximum

possible extent.'"   Atkins v. Virginia, 536 U.S. 304, 312

(2002), quoting Harmelin v. Michigan, 501 U.S. 957, 1000 (1991)

(Kennedy, J., concurring in part and concurring in the

judgment).   Proportionality "judgments should not be, or appear

to be, merely the subjective views of individual Justices,"

Rummel v. Estelle, 445 U.S. 263, 274 (1980), quoting Coker v.

Georgia, 433 U.S. 584, 592 (1977) (plurality opinion), and

therefore "courts should pay special attention to objective

factors deciding whether a practice violates 'the contemporary

standard of decency.'"   Libby, 385 Mass. at 431, quoting Rhodes

v. Chapman, 452 U.S. 337, 347 (1981).   See Coker, supra at 611

(Burger, C.J., dissenting), quoting Furman, 408 U.S. at 431

(Powell, J., dissenting) ("[W]here, as here, the language of the

applicable [constitutional] provision provides great leeway and

where the underlying social policies are felt to be of vital

importance, the temptation to read personal preference into the

Constitution is understandably great.   It is too easy to

propound our subjective standards of wise policy under the

rubric of more or less universally held standards of decency").

    "[T]he 'clearest and most reliable objective evidence of

contemporary values is the legislation enacted by the . . .

[L]egislature[].'"   Atkins, 536 U.S. at 312, quoting Penry v.

Lynaugh, 492 U.S. 302, 331 (1989).   See Gregg, 428 U.S. at 175,
                                                                    13

quoting, Furman, 408 U.S. at 383 (Burger, C.J., dissenting)

("[I]n a democratic society legislatures, not courts, are

constituted to respond to the will and consequently the moral

values of the people").   Thus, "[i]n divining contemporary

standards of decency, we may look to State statutes and

regulations, which reflect the public attitude as to what those

standards are."   Good, 417 Mass. at 335.   In other words, our

doctrinal framework for interpreting the text looks, in part, to

legislative judgments for objective evidence of contemporary

values.   When we infuse normative values into the open-ended

provisions of art. 26's proscription against "cruel or unusual

punishments," our doctrine protects against the great danger of

judges infusing their own values into their interpretation of

contemporary standards of decency by considering legislative

judgments as to crime and punishment.

    Beginning generally with legislation relating to

individuals from eighteen to twenty-one, our Commonwealth

considers these individuals adults, and has done so

unequivocally for more than forty years.    See G. L. c. 4, § 7,

Forty-eighth to Fifty-first, inserted by St. 1973, c. 925 ("In

construing statutes [in the Commonwealth] the following words

shall have the meanings herein given . . . :    'Minor' shall mean

any person under eighteen years of age. . . .    'Full age' shall

mean eighteen years of age or older. . . .     'Adult' shall mean
                                                                     14

any person who has attained the age of eighteen. . . .     'Age of

majority' shall mean eighteen years of age").   Individuals in

this category have been granted rights in Massachusetts

generally associated with adulthood.   See art. 3 of the

Amendments to the Constitution of the Commonwealth, as amended

through art. 100 of the Amendments (right to vote); G. L.

c. 234A, § 4 (serving on jury); G. L. c. 207, §§ 7, 24 (entering

marriage); G. L. c. 231, § 85O (entering contracts).2    This

includes the right to make decisions having potentially life-

altering effect.   See Norwood Hosp. v. Munoz, 409 Mass. 116,

122-123 (1991) (common-law and State constitutional right for

competent adults to refuse medical treatment, even where

treatment may be lifesaving).

     Nothing in the statutes that restrict certain activities to

individuals over the age of twenty-one alters or changes the age

at which the Legislature has determined adulthood begins.

Certainly none of the statutes on which the court or

     2 See also Office of Attorney General, When You Turn 18,
https://www.mass.gov/doc/your-guide-to-understanding-your-
rights-responsibilities-and-how-to-protect-yourself-when-you-
turn-18/download#:~:text=You're%2018!,and%20responsibilities
%20of%20an%20adult [https://perma.cc/QU9M-YV72] ("You're 18! In
Massachusetts you've now reached the age of legal adulthood.
With this milestone, you have nearly all the legal rights and
responsibilities of an adult. Among your new rights are the
right to vote and serve on a jury, to marry, to enlist in the
military or choose medical care, and to be responsible for any
contracts you sign").
                                                                  15

concurrences rely suggests that the activity restricted is

limited only to "adults."3   See G. L. c. 138, § 34 (must be

twenty-one years of age to purchase and sell alcoholic

beverages); G. L. c. 270, § 6 (must be twenty-one years of age

to purchase tobacco products), G. L. c. 140, § 131 (d) (iv)

(must be twenty-one years of age to obtain license to carry

handgun); G. L. c. 22C, § 10 (must be twenty-one years of age to

be State police officer); G. L. c. 31, § 58 (must be twenty-one

years of age to be municipal police officer); and G. L. c. 23K,

§ 25 (h) (must be twenty-one years of age to gamble or be in

gambling area).

     Article 26's requirements, however, are not adjudged by an

amorphous consideration of contemporary standards of decency as

they relate to age generally.   Those contemporary standards of

decency must relate to some extent to the crime and punishment

at hand.   After all, the relevant inquiry is whether the

     3 Relying on statutes that restrict or permit activities to
persons of a certain age is not an appropriate measure to
determine when society deems a person an adult, particularly
where those statutes do not expressly limit the activity to
"adults." For instance, several statutes restrict certain
activities to those over the age of sixteen, such as operating a
motor vehicle, G. L. c. 90, § 10, and working without a permit,
G. L. c. 149, § 90, but we would not consider those statutes as
evidence that a sixteen year old is an adult. Instead, the best
and most reliable evidence of when society considers the
beginning of adulthood is the point at which the Legislature
defines a person as an adult -- eighteen. See G. L. c. 4, § 7,
Fiftieth.
                                                                  16

challenged punishment is "cruel or unusual in light of

contemporary standards of decency."    Good, 417 Mass. at 335.

In this context, not only has the Legislature expressly provided

that individuals eighteen and older are adults in our

Commonwealth, see G. L. c. 4, § 7, Fiftieth, but it also has

determined that these individuals are responsible as adults in

our criminal justice system, see G. L. c. 119, §§ 52-54

(proceedings against children under eighteen in Juvenile Court

not deemed criminal).   This has included the mandatory

imposition of life without parole on individuals over eighteen

convicted of murder in the first degree.   See G. L. c. 265, § 2.

If the Legislature, responding to the will of the people, wished

to extend the age that individuals are treated as juveniles,

rather than adults, in our court system, it knows how to do so.

See St. 2013, c. 84, §§ 25, 26, amending G. L. c. 119, § 74

(expanding juvenile jurisdiction to eighteen year olds).

    Statutes and regulations throughout our Commonwealth do not

even suggest that contemporary standards of decency consider the

mandatory imposition of life without parole on adults from

eighteen to twenty-one to be cruel or unusual punishment for the

crime of murder in the first degree.   The sources upon which the

court relies do not address contemporary common views,

particularly as they relate to offenders within this age range

charged with murder.
                                                                     17

    To begin, the court's reliance on a statute authorizing

youthful offenders to be committed to the Department of Youth

Services until the age of twenty-one is misplaced.     That the

Legislature has designated, among several permissible

punishments for a child under the age of eighteen who has been

adjudicated a youthful offender, commitment to the Department of

Youth Services until the age of twenty-one is not relevant to

society's views of punishment for those who commit crimes while

eighteen or over, let alone the crime of murder.     See G. L.

c. 119, §§ 54, 58.     Rather, this is a sentencing scheme limited

to juveniles.   Moreover, the court relies on a task force formed

by the Legislature on emerging adults to suggest that

contemporary standards favor providing distinct treatment to

those from eighteen to twenty-one in our criminal legal system.

See ante at note 22.    However, the task force defined "emerging

adults" as individuals from ages eighteen to twenty-four, not

twenty-one, and in its report proposing certain changes to our

system applicable to this age group, it, importantly, excluded

from those changes the crime of murder.     Specifically, the task

force found, as the science demonstrates, see infra, that

individuals ages eighteen to twenty-four, "while possessing the

cognitive capacity to make deliberative decisions, are more

likely to be more impulsive, less future-oriented, more unstable

in emotionally charged settings, and more susceptible to peer
                                                                    18

and other outside influences."   Emerging Adults in the

Massachusetts Criminal Justice System:    Report of the Task Force

on Emerging Adults in the Criminal Justice System (Feb. 26,

2020), 2020 Senate Doc. No. 2840, at 6-7.    Even so, in making

its proposals for consideration by the Legislature, the task

force provided several options for changes to our current system

but excluded from all these proposals individuals of this age

group charged with the crime of murder.    Some examples included

extending the juvenile justice system, except in murder cases;

creating a "young adult offender" category, excluding high-level

offenses such as murder; providing judges with discretion to

refer certain cases to juvenile court, excluding high-level

offenses such as murder; and creating an "emerging adult" court

session, excluding individuals charged with the crime of murder.

Id. at 7, 9-10.

    Furthermore, although, as the defendant and Justice

Kafker's concurrence point out, the Advisory Sentencing

Guidelines (guidelines) recommended by the Massachusetts

Sentencing Commission in 2017 provide that research concerning

the brain development of emerging adults, which it defines as

individuals "up to and including age [twenty-one]" (emphasis

added), may be considered at sentencing, the guidelines are

intended to assist with discretionary sentencing and are

inapplicable to mandatory sentencing provisions such as those
                                                                    19

designated for the crime of murder in the first degree.    See

Massachusetts Sentencing Commission, Advisory Sentencing

Guidelines 4, 7-8 (Nov. 2017) ("In making these Sentencing

Guidelines advisory, rather than voluntary, the Commission

intends to provide a starting point for consideration, and not a

constraint on judicial discretion in fashioning an appropriate

sentence. . . .    [T]he Commission has no authority to abolish

minimum mandatory sentences or to change other statutory penalty

provisions").     More importantly, the guidelines do not reflect

public consensus, nor do they purport to do so.4    The guidelines

were never enacted by the Legislature, and thus have not taken

effect.   See G. L. c. 211E, § 3 (a) (1) ("The commission . . .

shall recommend sentencing guidelines, which shall take effect

only if enacted into law" [emphasis added]).

     The suggestion in Justice Kafker's and Justice Wendlandt's

concurrences that it is uncritical deference to the Legislature

that drives my conclusion that we must uphold the imposition of

     4 Within the guidelines themselves, the Massachusetts
District Attorneys Association responded in objection both to
the guidelines being issued to guide judges, without approval
and consent from the Legislature, and to the substance of the
guidelines based on the district attorneys' "collective
experience, the rights of victims of crime, the impact of the
opioid epidemic, and [the district attorneys'] vital role as
elected officials, protecting the public and representing the
public's interest" (footnote omitted). See Massachusetts
Sentencing Commission, Advisory Sentencing Guidelines 12-13
(Nov. 2017).
                                                                   20

life without parole on individuals from eighteen to twenty-one

deeply misunderstands my position.   It is our constitutional

doctrine looking to contemporary standards of decency that

commands that we consider our Legislature's judgments as to what

age constitutes adulthood.   We must ground our art. 26

proportionality analysis to reflect society's values as

expressed through legislative judgments.   The objective indicia

of contemporary standards of decency in our Commonwealth reflect

a societal view that individuals from eighteen to twenty-one are

adults, and nothing from these objective sources demonstrates

that society's evolving standards of decency consider the

mandatory imposition of life without parole to be cruel or

unusual when imposed on individuals within this age range who

have been convicted of murder in the first degree.

      These standards of decency are not unique to the

Commonwealth.   In ascertaining evolving standards of decency,

"judicial opinions and legislative actions at the State,

Federal, and international levels help to inform our

understanding of what art. 26 protects."   Okoro, 471 Mass. at

61.   As discussed in detail infra, thirty-six jurisdictions

permit the imposition of this punishment for this category of

homicide offenders, and only two States before today have

concluded, under their own Constitutions, that the mandatory
                                                                    21

imposition of life without parole on adults from eighteen to

twenty-one is cruel or unusual.5

     3.   Precedent.   Precedent relied on by the court is

specific to the sentencing of juveniles under the age of

eighteen and does not apply to the sentencing of adults.     When

considering the proportionality of a sentencing practice as it

relates to a particular class of offenders, precedent from both

the Supreme Court and this court distinguishes juveniles under

the age of eighteen from adults eighteen and older.

     The Supreme Court first made this distinction explicit in

Roper, 543 U.S. 551.    Looking to objective indicia of national

consensus and societal understandings, supported by scientific

and sociological studies, the Court concluded that the

imposition of the death penalty on juvenile homicide offenders

violates the Eighth Amendment's proscription against cruel and

unusual punishment.    See id. at 567-570.   Importantly, the Court

recognized in Roper that the qualities that distinguish

juveniles from adults "do not disappear when an individual turns

     5 The court's reliance on the twenty-three jurisdictions
that do not mandate life without parole for any crime regardless
of the age of the offender as evidence that contemporary
standards of decency deem cruel or unusual the imposition of
life without parole for offenders from eighteen to twenty-one
for the crime of murder in the first degree confounds logic. To
follow the court's reasoning would be to suggest that the
sentence of life without parole is cruel or unusual in the eyes
of contemporary standards of decency for any offender convicted
of the offense.
                                                                    22

[eighteen]."   Id. at 574.   Rather, because "[t]he age of

[eighteen] is the point where society draws the line for many

purposes between childhood and adulthood," the Court, deferring

to societal norms informed by legislative enactments, determined

eighteen to be the defining line at which a person may be

treated as an adult for the purpose of punishment.    Id. at 569,

574, Appendices B-D.   The cases following Roper have all

operated within this societal line.

      In Graham, 560 U.S. 48, the Court next addressed juveniles

convicted of nonhomicide offenses sentenced to life imprisonment

without the possibility of parole.    In answering the question of

proportionality, the Court again turned to objective indicia of

national consensus, expressed through legislative enactments and

State practice, and considered the culpability of juveniles as

compared to the severity of the punishment in order to inform

its own independent judgment whether the sentencing practice

violated the Eighth Amendment.    Id. at 61-63, 67.   This analysis

led the Court to conclude that, for juveniles who have not

committed homicide offenses, the imposition of life without

parole is cruel and unusual under the Eighth Amendment.      Id. at

82.

      Miller, 567 U.S. at 465, which followed Graham, formed the

basis for our jurisprudence in the Commonwealth concerning

proportionality as it relates to sentencing practices applied to
                                                                   23

juveniles.   In Miller, the Supreme Court held that "mandatory

life without parole for those under the age of [eighteen] at the

time of their crimes violates the Eighth Amendment's prohibition

on 'cruel and unusual punishments.'"   Id.   The Court in Miller

predicated its conclusion on two strands of precedent:     the

first, including Roper and Graham and their consideration of the

culpability of juveniles in light of the severity of the

sentences imposed; and the second, involving the prohibition

against the mandatory imposition of capital punishment due to

the absence of consideration of the individual characteristics

of the offender and the details of the offense.   See id. at 470.

    From Roper and Graham's teachings, the Court declared in

Miller that "children are constitutionally different from adults

for purposes of sentencing."   Miller, 567 U.S. at 471.    This

declaration rests firmly on principles of common sense, science,

and social science regarding children, their unique

characteristics, and how they have been treated in the law.       Id.

at 471-472, 481.   Based on these principles regarding children,

considered in conjunction with cases where individualized

sentencing is required before the death penalty is imposed, the

Court concluded that the Eighth Amendment requires an

individualized assessment of youth and its attendant
                                                                   24

characteristics before such a harsh penalty may be imposed on a

juvenile homicide offender.6   See id. at 475-477, 479-480.

     In so ruling in Miller, the Court emphasized that its

holding was limited to children, and that its precedent on adult

sentencing was not applicable to the sentencing of juvenile

offenders.   Id. at 481 ("Harmelin[, which addressed

constitutionality of life without parole sentence for adult

convicted of possessing 672 grams of cocaine,] had nothing to do

with children and did not purport to apply its holding to the

sentencing of juvenile offenders").    Indeed, as the Court noted,

"a sentencing rule permissible for adults may not be so for

children."   Id.   The Court cited several examples of punishments

that "generally comport[] with the Eighth Amendment" -- except

when it comes to children -- and emphasized that "'[o]ur history

is replete with laws and judicial recognition' that children

cannot be viewed simply as miniature adults.'"    Id., quoting

J.D.B. v. North Carolina, 564 U.S. 261, 274 (2011).    And thus,

     6 Because the decision in Miller did not categorically bar a
penalty for a class of offenders but was based on principles
established in Roper and Graham, as well as the Supreme Court's
individualized sentencing cases, the Court relied less on
"objective indicia of society's standards" to gauge a national
consensus. See Miller, 567 U.S. at 483. The Court,
nevertheless, surveyed the various jurisdictions and counted
twenty-nine (twenty-eight States and the Federal government)
that mandatorily imposed life without parole on juvenile
homicide offenders. Id. at 482-483 & n.9.
                                                                  25

the Court noted, "it is the odd legal rule that does not have

some form of exception for children."7   Miller, supra.

     With this Supreme Court precedent concerning juvenile

sentencing as the foundation, we decided Diatchenko I, 466 Mass.

at 657-658.   Our inquiry in Diatchenko I was limited and

precise, given Miller's prior determination that the mandatory

imposition of life without the possibility of parole for

juvenile offenders was disproportionate under the Eighth

Amendment.    See Diatchenko I, supra at 667 ("Pursuant to Miller,

[567 U.S. at 479, 489], we conclude that this mandatory sentence

violates both the Eighth Amendment prohibition against 'cruel

and unusual punishment[]' and the analogous provision of the

Massachusetts Declaration of Rights set forth in art. 26").     The

remaining question for us in Diatchenko I was whether an

individualized assessment of a juvenile offender could ever

     7 It is worth noting that when the Supreme Court has
assessed whether punishment is barred by the Eighth Amendment
when applied to a category of offenders who are not juveniles,
it has placed great emphasis on contemporary standards of
decency, gleaned from legislative judgments. See Atkins, 536
U.S. at 313-316, 321 (death penalty for intellectually disabled
unconstitutional, determined by "review[ing] the judgment of
legislatures that have addressed the suitability of imposing the
death penalty on the [intellectually disabled] and then
consider[ing] reasons for agreeing or disagreeing with their
judgment"); Ford v. Wainwright, 477 U.S. 399, 406-410 (1986)
(death penalty for insane prisoners unconstitutional where
execution of them was condemned at common law, and at time of
decision "no State in the Union permit[ted] the execution of the
insane").
                                                                    26

constitutionally justify the imposition of life without parole

under art. 26.   Id. at 668.   We concluded that the answer to

that singular question was no.    Id. at 670-671.   In light of the

unique characteristics of juvenile offenders, we concluded that

an individualized assessment could never result in a

determination that a juvenile was "irretrievably depraved," at

the time of sentencing, such that "a sentence of life without

parole should be imposed on a juvenile homicide offender."       Id.

at 670, quoting Roper, 543 U.S. at 570.

    While we relied on "current scientific research on

adolescent brain development," combined with "the myriad

significant ways that this development impacts a juvenile's

personality and behavior," in Diatchenko I, 466 Mass. at 669, to

make this determination, our focus was on a legislatively

defined category of individuals constitutionally deserving of

special treatment.   We did not look to science to carve out this

group; legislation had already defined it.    See id. at 659 n.8.

We determined that, "under art. 26, the 'unique characteristics

of juvenile offenders' should weigh more heavily in the

proportionality calculus than the United States Supreme Court

required under the Eighth Amendment," Commonwealth v. Perez, 477

Mass. 677, 683 (2017), S.C., 480 Mass. 562 (2018), quoting

Diatchenko I, supra at 671, and we used scientific research to

augment this weighing.
                                                                       27

       Two features of our decision in Diatchenko I render it

unsuited and unable to answer the question before us today.       The

first, and most pronounced, reason:       it was limited to juveniles

under the age of eighteen.       See Diatchenko I, 466 Mass. at 659

n.8.       More specifically, the decision was limited to a class of

offenders predefined by the Legislature as juveniles.       Indeed,

the decision in Diatchenko I made painstakingly clear that its

holding was restricted to juvenile offenders under the age of

eighteen.8      Justice Kafker's concurrence poses the question

       See Diatchenko I, 466 Mass. at 658-659 ("We further
       8

conclude that the mandatory imposition of a sentence of life in
prison without the possibility of parole on individuals who were
under the age of eighteen when they committed the crime of
murder in the first degree violates the prohibition against
'cruel or unusual punishments' in art. 26 of the Massachusetts
Declaration of Rights, and that the discretionary imposition of
such a sentence on juvenile homicide offenders also violates
art. 26 because it is an unconstitutionally disproportionate
punishment when viewed in the context of the unique
characteristics of juvenile offenders" [emphases added]); id. at
669 ("In the present circumstances, the imposition of a sentence
of life in prison without the possibility of parole for the
commission of murder in the first degree by a juvenile under the
age of eighteen is disproportionate not with respect to the
offense itself, but with regard to the particular offender"
[emphasis added]); id. at 671 ("With current scientific evidence
in mind, we conclude that the discretionary imposition of a
sentence of life in prison without the possibility of parole on
juveniles who are under the age of eighteen when they commit
murder in the first degree violates the prohibition against
'cruel or unusual punishment[]' in art. 26" [emphasis added]);
id. ("Given the unique characteristics of juvenile offenders,
they should be afforded, in appropriate circumstances, the
opportunity to be considered for parole suitability" [emphasis
added]); id. at 673 ("In light of our conclusion that the
imposition of a sentence of life in prison without the
possibility of parole on juvenile offenders who are under the
                                                                     28

"whether there is a meaningful constitutional difference between

overruling the Legislature's decision that it is permissible to

sentence juveniles to life in prison without the possibility of

parole and overruling the Legislature's decision that it is

permissible to sentence eighteen through twenty year olds to

life in prison without the possibility of parole."     See ante

at   .     But Diatchenko I answers that question; there is.   The

decision in Diatchenko I rested on the recognition that

juveniles are "constitutionally different from adults for

purposes of sentencing."    Id. at 670, 674, quoting Miller, 567

U.S. 460, 471.    See Diatchenko I, supra at 675 (Lenk, J.,

concurring) ("Pivotal to this holding . . . is the recognition

that 'children are constitutionally different from adults for

purposes of sentencing'" [citation omitted]).    In Diatchenko I,

we did not venture to determine who qualified as a juvenile or

look to science to draw the line between childhood and

adulthood; instead, we relied on the prefixed line established

by society and the Legislature to issue our holding.     See id. at

659 n.8.    Where that prefixed line places eighteen, nineteen,

and twenty year olds on the side of adulthood, and thus not

age of eighteen when they commit the crime of murder in the
first degree is unconstitutional, the language in the fourth
sentence of G. L. c. 265, § 2, which sets forth the exception to
parole eligibility, is invalid as applied to juvenile homicide
offenders" [emphases added]).
                                                                    29

entitled to distinct constitutional treatment, Diatchenko I does

not dictate the result here.   As the Supreme Court in Miller

underscored, precedent relating to adult sentencing is not

applicable to juveniles, and inversely, precedent relating to

juvenile sentencing is not applicable to adults.    See Miller,

567 U.S. at 481.

    The second reason Diatchenko I cannot resolve the

categorical question in this case relates to the court's inquiry

there and the reliance on science to assess proportionality.       As

discussed infra, science is important when considering

proportionality as it relates to the offender.     Diatchenko I,

466 Mass. at 669-670, establishes that.   But, as the court, the

concurrences, and the parties all must and, at least implicitly,

do acknowledge, science alone cannot determine whether a

sentence is constitutionally disproportionate under art. 26.

See ante at note 30 (court's opinion), note 9 (Kafker, J.,

concurring), note 7 (Wendlandt, J., concurring).    Because the

Supreme Court in Miller had already undertaken a proportionality

analysis, considering primarily precedent, augmented by science

and contemporary standards, and it deemed the mandatory

imposition of life without parole on juveniles unconstitutional,

our own proportionality analysis was abbreviated and related

only to the discretionary imposition of that sentence.

Diatchenko I, supra at 670-671.   We relied on Miller, as well as
                                                                   30

its consideration of Graham and Roper, for the proportionality

calculus as it relates to the mandatory imposition of life

without parole on juveniles.   But in light of our determination

that art. 26 is more protective than the Eighth Amendment, we

looked to science, as well as sociological understandings,

concerning youth to render our decision regarding the

discretionary imposition of life without parole on juveniles,

and only on juveniles.   Diatchenko I, supra.

    4.   Science.   Importantly, we have never suggested that

scientific research untethered to any legislation can create a

new category of individuals entitled to special treatment under

our Constitution.   In creating such a category, the court

impermissibly engages in legislative line drawing, detached from

our constitutional analysis.   To demonstrate this, one need look

no further than the location of the line drawn.   The court

includes within its category of "emerging adults" individuals

from eighteen to twenty-one.   See ante at note 1.   This line,

once framed by the defendant as being properly placed at the age

of twenty-two, was urged to be drawn at twenty-one on remand

when the case was paired with Commonwealth v. Robinson, 493

Mass.    (2023).

    Although the judge's factual findings are limited to

individuals eighteen through twenty years old, much of the

scientific expert testimony and studies supporting those
                                                                  31

findings included individuals twenty-one years of age (and in

some instances older) as it relates to impulsivity, self-

regulation in an emotionally aroused state, sensation seeking,

and brain plasticity.   Both of the experts who testified for the

defendant, Drs. Adriana Galván and Robert Kinscherff, defined

"young adults" or "late adolescents" to include twenty-one year

old individuals, and their testimony concerning brain maturity

often extended to those individuals.   While Dr. Laurence

Steinberg purported to limit his testimony to eighteen,

nineteen, and twenty year olds, the research articles in the

record that he coauthored, and which undergirded his testimony,

grouped together individuals eighteen through twenty-one years
                                                                 32

old ,9 and in some instances through twenty-two years old.10

Galván was also involved in the studies that routinely grouped

     9 See Breiner et al., Combined Effects of Peer Presence,
Social Cues, and Rewards on Cognitive Control in Adolescents, 60
Developmental Psychobiology 292, 292-294 (2018) ("The final
participant sample consisted of 71 adolescents [ages 13-17 years
old, M = 15.48, SD = 1.24; 33 males, 38 females]; 48 young
adults [ages 18-21 years-old, M = 19.64, SD = 1.03; 25 males, 23
females]; and 57 adults [ages 22-25 years-old, M = 23.34, SD =
1.01; 28 males, 29 females]"); Cohen et al., When Is an
Adolescent an Adult? Assessing Cognitive Control in Emotional
and Nonemotional Contexts, 27 Psychol. Sci. 549, 550 (2016) ("A
total of 110 usable scans were included in the final analyses
reported here [41 teens -- 23 females and 18 males, ages 13-17
years, M = 16.19, SD = 1.20; 35 young adults -- 17 females and
18 males, ages 18-21 years, M = 19.88, SD = 1.09; 34 adults --
17 females and 17 males, ages 22-25 years, M = 24.08, SD =
1.04"); Icenogle et al., Adolescents' Cognitive Capacity Reaches
Adult Levels Prior to Their Psychosocial Maturity: Evidence for
a "Maturity Gap" in a Multinational, Cross-Sectional Sample, 43
Law & Hum. Behav. 69, 74 (2019) (participants divided into seven
age groups: "10-11 years, 12-13 years, 14-15 years, 16-17
years, 18-21 years, 22-25 years, and 26-30 years"); Rudolph et
al., At Risk of Being Risky: The Relationship Between "Brain
Age" under Emotional States and Risk Preference, Developmental
Cognitive Neurosci., vol. 24, 2017, at 93-94 ("all participants
-- M = 19.05, SD = 3.91; 11 children -- 6 female, ages 10-12
years, M = 11.55, SD =0.89; 80 teens -- 45 female, ages 13-17
years, M = 15.77, SD = 1.44; 58 young adults -- 33 females, ages
18-21 years, M = 19.86, [SD = ]1.11; 63 adults -- 34 females,
ages 22-25 years, M = 23.7, SD = l.03"); Steinberg et al.,
Around the World, Adolescence Is a Time of Heightened Sensation
Seeking and Immature Self-Regulation, Developmental Sci., vol.
21, Mar. 2018, at 6 ("each study site attempted to recruit at
least 30 males and 30 females from each of seven age groups:
10-11 years, 12-13 years, 14-15 years, 16-17 years, 18-21 years,
22-25 years, and 26-30 years").

     10See Chein et al., Peers Increase Adolescent Risk Taking
by Enhancing Activity in the Brain's Reward Circuitry,
Developmental Sci., vol. 14, Mar. 2011, at 3 ("Data from 40
subjects [14 adolescents -- eight female, ages 14-18 years, M =
15.7, SD = 1.5; 14 young adults -- seven female, ages 19-22
years, M = 20.6, SD = 0.9; and 12 adults -- six female, ages 24-
                                                                  33

eighteen through twenty-one year old individuals together.    And,

notably, her testimony concerning brain plasticity -- the

ability to change in response to different circumstances or

environment -- indicated development until the mid-twenties.     If

twenty-one year old individuals, and even beyond, suffer from

the same brain deficiencies as eighteen, nineteen, and twenty

year old individuals, by the court's logic, the mandatory

imposition of life without parole on them must too be

unconstitutional.   However, because the defendant cut off his

request for relief at the age of twenty-one, the court does not

conclude as much.   Accordingly, not only is the line at twenty-

29 years, M = 25.6, SD = 1.9] were included in analyses");
Gardner & Steinberg, Peer Influence on Risk Taking, Risk
Preference, and Risky Decision Making in Adolescence and
Adulthood: An Experimental Study, 41 Developmental Psychol.
625, 625-627 (2005) ("In this study, 306 individuals in 3 age
groups -- adolescents [13–16], youths [18–22], and adults [24
and older] -- completed 2 questionnaire measures assessing risk
preference and risky decision making, and 1 behavioral task
measuring risk taking"); Silva et al., Adolescents in Peer
Groups Make More Prudent Decisions When a Slightly Older Adult
Is Present, 34 Psychol. Sci. 322, 323 (2016) ("In the present
study, we investigated how the presence of peers affects
decision making among late adolescents [ages 18–22] and whether
the previously documented effect of peers on adolescents' risk
taking can be reduced or reversed by the presence of a slightly
older adult [age 25–30]"); Silva et al., Peers Increase Late
Adolescents' Exploratory Behavior and Sensitivity to Positive
and Negative Feedback, 26 J. Res. on Adolescence 696, 697 (2015)
("We focus on late adolescents [ages 18-22] because there is
considerable evidence that the prevalence of certain real-life,
high-stakes risk behaviors [e.g., binge drinking, substance use,
reckless driving, and unprotected sex] is highest among 18- to
22-year olds").
                                                                   34

one not crafted by the Legislature or society, as it must be, it

is not even scientifically crafted.   In this area of crime and

punishment particularly, the court must resist judicially

crafting this line.   See Commonwealth v. Brown, 466 Mass. 676,

685 (2013), S.C., 474 Mass. 576 (2016) (expressing "concern for

judicial law-making" in area of "defining crimes and their

punishments" [citation omitted]).

    The problem with the court defining this category of

individuals based on science is not only that the science it

uses applies beyond the chronological category that the court

creates, but also that neuroscience does not limit itself to

young adults.   If we look only to neuroscience to determine who

is or who is not entitled to distinct constitutional treatment

for sentencing purposes, what categories are off limits?     The

court, purportedly based on science, creates the category of

"emerging adults," but what about declining adults with

dementia; those with early-onset Alzheimer's disease; those with

brain tumors or genetic deficiencies; and those with a low

intelligence quotient, but not low enough to constitute an

intellectual disability?

    In advocating against unilaterally drawing the line of

adulthood beyond the age of eighteen -- where the Legislature

and society have placed it -- I do not discount that the current

scientific research on the brain development of individuals ages
                                                                    35

eighteen to twenty-one (and, in some instances, to mid-twenties)

shows deficiencies in the ability to self-regulate in

emotionally arousing situations, as well as increased sensation

seeking and susceptibility to peer pressure.    Nor do I disregard

the research on developmental brain plasticity and its

continuation into an individual's mid-twenties, suggesting a

greater capacity for change.    The judge found the scientific

experts to be reliable.    Policy considerations, however, are for

the Legislature.    Our role in this area of crime and punishment

is limited, and we must remain disciplined when assessing

whether the punishment, chosen by the Legislature, is so

disproportionate that it "shocks the conscience and offends

fundamental notions of human dignity" to reach the level of

cruel or unusual.    Cepulonis, 384 Mass. at 497, quoting Jackson,

369 Mass. at 910.

    The challenged punishment in this case is not.

Contemporary standards of decency, ascertained properly through

objective sources, consider these individuals adults and do not

remotely suggest a societal attitude or consensus that

mandatorily imposing life without the possibility of parole on

such individuals when they commit murder in the first degree is

cruel or unusual.    As a result, precedent relating to the

sentencing of juveniles, who are constitutionally different from

adults for purposes of sentencing, is inapplicable.    Scientific
                                                                  36

research cannot create a category of individuals entitled to

specialized constitutional treatment, and indeed, it does not

support the category created by the court.    Further, when we

look beyond just the nature of the offender and consider other

factors relevant to the proportionality analysis, see infra, it

becomes clear that this punishment does not violate art. 26.

    5.   Applicability of tripartite proportionality analysis.

Although the considerations on which the court bases its

decision -- contemporary standards of decency, science, and

precedent -- do not support its conclusion that the mandatory

imposition of life without parole on individuals from eighteen

to twenty-one reaches the level of constitutional

disproportionality, I would not abandon application of the

tripartite analysis for evaluating categorical challenges to the

proportionality of a sentencing practice.    Contemporary

standards, science, and precedent are all important to assessing

proportionality, but, as the court considers them, each focuses

only on the nature of the offender.   The proportionality

analysis under art. 26 requires a more comprehensive inquiry.

See Commonwealth v. Sharma, 488 Mass. 85, 89, quoting

Commonwealth v. Concepcion, 487 Mass. 77, 86, cert. denied, 142

S. Ct. 408 (2021) (tripartite analysis "requires [1] an 'inquiry

into the nature of the offense and the offender in light of the

degree of harm to society,' [2] 'a comparison between the
                                                                  37

sentence imposed here and punishments prescribed for the

commission of more serious crimes in the Commonwealth,' and [3]

'a comparison of the challenged penalty with the penalties

prescribed for the same offense in other jurisdictions'").

    We adopted the tripartite analysis in Jackson, 369 Mass. at

910, and have, thus far, not confined it to individual

proportionality challenges.   As the court recognizes, see ante

at note 12, we have on multiple occasions used the tripartite

analysis to evaluate categorical challenges to the

proportionality of sentencing provisions based on the nature of

the offense, without considering the individual circumstances of

an offender sentenced according to those provisions.     See

Commonwealth v. Therriault, 401 Mass. 237, 239-240 (1987)

(challenge to one-year minimum mandatory prison term for

homicide by motor vehicle while intoxicated); Opinions of the

Justices, 378 Mass. at 829 (facial examination whether proposed

"bills' mandatory sentencing provisions -- including the

requirement that a twenty-five year mandatory sentence in State

prison be imposed on persons found manufacturing, distributing

dispensing, or possessing with intent to distribute, certain

narcotics having a street value in excess of $25,000" -- were

constitutionally disproportionate); Jackson, supra at 909

(challenge to one-year mandatory sentence imposed for carrying

firearm without license).
                                                                     38

    Additionally, we have used the tripartite analysis to hold

that a sentencing practice is constitutionally disproportionate,

at least presumptively, when applied to an entire category of

individuals.   See Perez, 477 Mass. at 686 (concluding, based on

application of tripartite analysis, that "a juvenile defendant's

aggregate sentence for nonmurder offenses with parole

eligibility exceeding that applicable to a juvenile defendant

convicted of murder is presumptively disproportionate," and that

only after hearing according to Miller, 567 U.S. at 479, could

that presumption be rebutted).

    While, in Diatchenko I, we did not expressly state whether

we were or were not considering the tripartite analysis, our

conclusion was based on the considerations associated with the

first prong of the tripartite analysis:   "the imposition of a

sentence of life in prison without the possibility of parole for

the commission of murder in the first degree by a juvenile under

the age of eighteen is disproportionate not with respect to the

offense itself, but with regard to the particular offender"

(emphasis added).   See Diatchenko I, 466 Mass. at 669.

Importantly, in cases where we have explicitly applied the

tripartite analysis, we have cited this portion of our decision

in Diatchenko I for its applicability to the first prong of the

tripartite analysis.   See Concepcion, 487 Mass. at 88;

Commonwealth v. LaPlante, 482 Mass. 399, 406 (2019).      See also
                                                                    39

Perez, 477 Mass. at 684-685 (discussing applicability of

Diatchenko I's reasoning to first prong of tripartite

framework).

     Diatchenko I's reliance on just one prong of the tripartite

analysis to assess proportionality is not unique.    In addition

to Diatchenko I, we have made determinations, both in favor and

against proportionality, by analyzing less than all three prongs

of the tripartite test.     See Perez, 477 Mass. at 685-687

(because sentence in that case was disproportionate under first

two prongs of tripartite analysis, court "need not discuss the

third prong").   See also LaPlante, 482 Mass. at 404 n.4 (where

no "more serious crimes" to be compared with defendant's, "case

defie[d] direct application of the second . . . prong" of

tripartite analysis).     That all three prongs of the tripartite

analysis do not fit neatly in every circumstance does not

justify now abandoning its application for categorical

challenges.11

     I would not discard this well-established framework,

particularly in cases like this.     The tripartite analysis was

adopted to cabin the "inherent subjectivity" involved in

     11California, the jurisdiction from which we adopted the
tripartite analysis, has applied the analysis to assess whether,
categorically, the imposition of life without parole on
offenders younger than sixteen convicted of kidnapping is
disproportionate under its own State Constitution. See In re
Nuñez, 173 Cal. App. 4th 709, 725-731 (2006).
                                                                     40

assessing proportionality.   See Opinions of the Justices, 378

Mass. at 830.   See Harmelin, 501 U.S. at 986 ("the

proportionality principle becomes an invitation to imposition of

subjective values").   Where the analysis involves questions,

such as whether a punishment "shocks the conscience," "offends

fundamental notions of human dignity," or is in accord with

contemporary standards of human decency, the issue of

disproportionality is vulnerable to a subjective approach; the

framework was developed intentionally to combat subjectivity and

create objective criteria to guard against improper judicial

encroachment on exclusively legislative territory.    See Opinions

of the Justices, 378 Mass. at 830; Jackson, 369 Mass. at 910.

See also Atkins, 536 U.S. at 312, quoting Harmelin, supra at

1000 ("Proportionality review under those evolving standards

should be informed by '"objective factors to the maximum

possible extent"'").

    The issue of subjectivity is central to my concern with the

court's decision not to apply the tripartite analysis.     When we

deviate from the objective framework developed to mitigate

subjectivity, we risk infusing our own personal values into the

open-ended provisions of the Constitution, which fosters

mistrust that threatens the continued vitality of judicial

review and an abiding respect for the judiciary.     With this in
                                                                    41

mind, I would apply the doctrinal framework adopted specifically

to guard against these concerns.

    a.   First prong.   Under the first prong of the tripartite

analysis for analyzing proportionality, we consider "the nature

of the offense and the offender in light of the degree of harm

to society."   Jackson, 369 Mass. at 910.   The considerations of

contemporary standards of decency, science, and precedent

addressed supra, and addressed by the court ante, examine

proportionality as it relates to the nature of the offender.

These considerations, however, do not consider the nature of the

offense in light of the harm to society, which must also take

into account the Legislature's legitimate reasons for imposing

such a punishment.   See Jackson, supra ("The penological

purposes of the prescribed punishment are also relevant to this

analysis . . .").

    The nature of the offense of murder and the harm the crime

inflicts on society and its victims warrant a punishment

commensurate with the crime.   Cf. Jackson, 369 Mass. at 910.

"Clearly the severity of the penalty, in the case of a serious

offense, is not enough to invalidate it where the nature of the

penalty is rationally directed to achieve the legitimate ends of

punishment."   Id., quoting Trop v. Dulles, 356 U.S. 86, 111

(1958) (Brennan, J., concurring).   Imposing a punishment

commensurate with the crime "reflects society's and the victim's
                                                                     42

interests in seeing that the offender is repaid for the hurt he

caused."   Kennedy v. Louisiana, 554 U.S. 407, 442 (2008).

"Society is entitled to impose severe sanctions . . . to express

its condemnation of the crime and to seek restoration of the

moral imbalance caused by the offense."     Graham, 560 U.S. at 71.

    The penological justifications for imposing life without

the possibility of parole are incapacitation, deterrence, and

retribution.   See Diatchenko I, 466 Mass. at 670-671.    Since the

punishment the Legislature has chosen to further these goals

neither "shocks the conscience" nor offends "contemporary

standards of decency which mark the progress of society"

(citations omitted), id. at 669, it is not within our authority

to question the wisdom of this decision, so long as the sentence

is not "so totally without penological justification that it

results in the gratuitous infliction of suffering," Gregg, 428

U.S. at 183.   See id. at 182-183 ("we cannot invalidate a

category of penalties because we deem less severe penalties

adequate to serve the ends of penology" [citation and quotation

omitted]).

    b.     Second prong.   The second prong involves "a comparison

between the sentence imposed here and punishments prescribed for

the commission of more serious crimes in the Commonwealth."

Sharma, 488 Mass. at 89, quoting Concepcion, 487 Mass. at 86.

As with other cases where we have applied the tripartite
                                                                    43

framework, because the crime of murder in the first degree is

the most serious offense in the Commonwealth, and the punishment

of life without the possibility of parole, which is imposed

mandatorily for this crime, is the most severe punishment in the

Commonwealth, this case "defies direct application of the second

. . . prong" of the tripartite analysis.       LaPlante, 482 Mass. at

404 n.4.    We turn then to the third prong.

     c.    Third prong.   Under the third prong of the tripartite

analysis, we compare "the challenged penalty with the penalties

prescribed for the same offense in other jurisdictions."

Sharma, 488 Mass. at 89, quoting Concepcion, 487 Mass. at 86.

     The court cites at least ten States that currently mandate

the imposition of life without the possibility of parole on all

adult offenders convicted of an offense equivalent to murder in

the first degree in the Commonwealth –- a count that does not

include the Federal government, which also does so.      See ante at

note 26.    One State, Michigan, mandatorily imposes life without

the possibility of parole for offenders over the age of eighteen

convicted of such a crime.    See People v. Parks, 510 Mich. 225,

268 (2022).12

     12And at least nine more States mandate a sentence of life
without the possibility of parole for adult offenders
adjudicated guilty of murder under certain circumstances. The
Michigan Supreme Court cited six such jurisdictions:
"California, Cal. Penal Code [§] 190.2; Connecticut, Conn. Gen.
Stat. [§§] 53a-35a and 53a-54b; Hawaii, Haw. Rev. Stat.
                                                                 44

     While not legislatively mandated, sixteen States and the

District of Columbia authorize the imposition of life without

the possibility of parole on adult offenders convicted of a

crime equivalent to what the Commonwealth defines as murder in

the first degree,13 while others authorize similarly harsh

[§§] 706-656 and 706-657; Kansas, Kan. Stat. Ann. [§§] 21-6620,
21-5401(a)(6), and 21-6617; Texas, Tex. Penal Code Ann.
[§§] 12.31 and 12.32; and Vermont, Vt. Stat. Ann., tit. 13,
§§ 2303 and 2311." Parks, 510 Mich. at 263 n.16. I also found
the following: New Jersey, N.J. Stat. Ann. § 2C:11-3; Oregon,
Or. Rev. Stat. § 163.107; and Virginia, Va. Code Ann. §§ 18.2-
10, 18.2-31, 18.2-32. Indeed, some of these States impose life
imprisonment without the possibility of parole on less egregious
grounds than the standard in Massachusetts of deliberate
premeditation; extreme atrocity or cruelty; or actual malice in
the commission or attempted commission of a crime punishable
with life imprisonment.

     13These jurisdictions include Georgia, Ga. Code Ann. § 16-
5-1; Indiana, Ind. Code § 35-50-2-3; Kentucky, Ky. Rev. Stat.
Ann. §§ 507.020, 532.030; Maine, Me. Rev. Stat. tit. 17-A,
§ 1603, § 2314; Montana, Mont. Code Ann. § 45-5-102(2); Nevada,
Nev. Rev. Stat. § 200.030; New Mexico, N.M. Stat. Ann. §§ 30-2-
1, 31-18-14; North Dakota, N.D. Cent. Code §§ 12.1-16-01, 12.1-
32-01; Oklahoma, Okla. Stat. tit. 21, § 701.9; South Carolina,
S.C. Code Ann. § 16-3-20; Tennessee, Tenn. Code Ann. § 39-13-
202; Vermont, Vt. Stat. Ann. tit. 13, § 2303; West Virginia, W.
Va. Code §§ 61-2-2, 62-3-15; and Wyoming, Wyo. Stat. Ann. § 6-2-
101. Additionally, the District of Columbia, Hawaii, and
Illinois permit the imposition of life without parole for
murders committed in heinous, atrocious, or cruel circumstances
comparable to murder in the first degree in the Commonwealth
under the theory of extreme atrocity or cruelty. See D.C. Code
§ 22-2104.01 (where murder was especially heinous, atrocious, or
cruel); Haw. Rev. Stat. § 706-657 (where murder in second degree
was especially heinous, atrocious, or cruel); 730 Ill. Comp.
Stat. 5/5-8-1 (where "murder was accompanied by exceptionally
brutal or heinous behavior indicative of wanton cruelty").
                                                                   45

sentences for the equivalent crime.14   Accordingly, when viewed

in total, thirty-six jurisdictions (thirty-four States, the

Federal government, and the District of Columbia) legislatively

authorize the imposition of life without the possibility of

parole for adult offenders -- including those ages eighteen,

nineteen, and twenty -- convicted of the equivalent of murder in

the first degree.   See Jackson, 369 Mass. at 913 (considering

States that permit same or similar punishment, even if not

mandated).

     No jurisdiction has categorically prohibited by judicial

decision the imposition of this penalty for homicide offenders

eighteen and older as cruel or unusual punishment.   While, as

the court notes, Washington and Michigan have declared, under

their own State Constitutions, that the mandatory imposition of

life without parole on eighteen through twenty year old

individuals (Washington) and eighteen year old individuals

(Michigan), respectively, is unconstitutional, see Matter of the

Personal Restraint of Monschke, 197 Wash. 2d 305, 312 (2021);

     14For example, Alaska and New Jersey both impose a minimum
of thirty years imprisonment without parole eligibility for
murder in the first degree. See Alaska Stat. § 12.55.125; N.J.
Stat. Ann. § 2C:11-3.
                                                                  46

Parks, 510 Mich. at 268, this hardly represents a consistent

trend.15   See ante at   .

     Where the challenged penalty in this case, when imposed on

individuals from eighteen to twenty-one, is permitted by thirty-

six jurisdictions across the country and is specifically

mandated in eleven jurisdictions; where other jurisdictions

impose similarly harsh penalties for similar crimes; and where

no other jurisdiction has interpreted its Constitution as

     15Moreover, both Michigan and Washington have
constitutional requirements that differ from our own. Michigan,
for instance, permits juveniles to be sentenced to life without
the possibility of parole following an individualized hearing.
See People v. Taylor, 510 Mich. 112, 128 (2022). Thus, in
imposing such a requirement for eighteen year old offenders
under its State Constitution, the Michigan Supreme Court looked
to Miller for guidance, without having to wrestle with
Diatchenko-like precedent deeming such discretionary sentencing
unconstitutional. See Parks, 510 Mich. at 265-266. While the
Washington Supreme Court has interpreted its Constitution to bar
both the mandatory and discretionary imposition of life without
parole for juvenile offenders, as we have, in the case in which
that court permitted such a punishment to be imposed on eighteen
to twenty year old offenders after an individualized hearing,
unlike in this case, there was no argument that the punishment
should be categorically barred as unconstitutional for that
class of offenders. See Matter of the Personal Restraint of
Monschke, 197 Wash. 2d at 325. Moreover, in making such a
determination, the Washington Supreme Court declined to apply
either of its constitutional tests for assessing whether a
punishment is categorically cruel under its Constitution. Id.
at 312. The court's own precedent in State v. Fain, 94 Wash. 2d
387 (1980), and State v. Bassett, 192 Wash. 2d 67 (2018), called
for the application of a proportionality test and a categorical
bar analysis when considering cruelty. The court deferred to
neither of these controlling doctrines in making its decision.
Matter of the Personal Restraint of Monschke, supra. Thus, its
constitutional analysis as it relates to this punishment for
this class of offenders diverges significantly from our own.
                                                                  47

requiring mandatory parole eligibility for adults from eighteen

to twenty-one, the disparity between Massachusetts and others

reflects nothing "more than different exercises of legislative

judgment . . . a difference between unrestrained power and that

which is exercised under the spirit of constitutional

limitations formed to establish justice."    Jackson, 369 Mass. at

914, quoting Weems, 217 U.S. at 381.    It does not lend itself to

a conclusion that the imposition of life without parole on

individuals eighteen, nineteen, and twenty years old, who have

been convicted of murder in the first degree, violates art. 26.

See Cepulonis, 384 Mass. at 499 (where difference between

punishment in Massachusetts and "that prescribed in other States

is merely one of degree[,] [i]t is not violative of art. 26 or

of the Eighth Amendment").

    Conclusion.   As the judiciary, we must proceed with extreme

restraint when exercising our power to review punishment

designated by the Legislature to determine whether it exceeds

the bounds of art. 26's requirements.    Applying the analysis

specifically established to cabin our review when assessing

proportionality under art. 26, the punishment that the

Legislature prescribed in this case, when applied to individuals

from eighteen to twenty-one, is not so disproportionate to this

class of offenders, nor the crime of murder in the first degree,

particularly in light of the harm caused to society by murder in
                                                                  48

the first degree and the Legislature's legitimate justifications

for imposing such a punishment.   In the Commonwealth,

individuals eighteen and older are considered adults; they

receive the rights and consequences associated with adulthood;

and the contemporary standards of decency, expressed through

legislation, demonstrate support for this severe punishment for

this most severe crime.

    While the scientific research concerning the brain function

and development of eighteen through twenty-five year old

individuals may cause the Legislature to consider raising the

age of individuals convicted of murder in the first degree who

are entitled to parole eligibility, where, under our

constitutional framework, the punishment is not "so

disproportionate" that it "shocks the conscience and offends

fundamental notions of human dignity," Cepulonis, 384 Mass. at

497, quoting Jackson, 369 Mass. at 910, it does not violate art.

26's proscription against cruel or unusual punishment.   I

respectfully dissent.
    CYPHER, J. (dissenting).     A significant amount of time and

energy has been expended to prove through science what the

Legislature knew when it promulgated its first statute

concerning juveniles:   young males take more risks and are more

impulsive than older males.    See R.S. (1836), c. 143, § 18

(providing that certain children convicted of offense punishable

by incarceration in State prison shall instead serve sentence in

house of correction or county jail); Governor's Anti-Crime

Council, Juvenile Code Study and Revision Project, History of

Massachusetts Statutes Relating to Delinquent Youth 1 (July

1985) ("[The] pattern of treating juvenile offenders [in

Massachusetts] differently than their adult counterparts began"

with adoption of Revised Statutes of 1836).

    Whether this court should eliminate the imposition of

mandatory sentences of life imprisonment without the possibility

of parole for those convicted of murder in the first degree who

were from age eighteen to twenty at the time of the crime

implicates many important considerations.   The most significant

consideration for us in this case is whether the sentencing

scheme violates art. 26 of the Massachusetts Declaration of

Rights, the prohibition against cruel or unusual punishment.    If

it does not violate art. 26, then we must admit that, however we

may view life sentences without parole, for any age over

seventeen or as mandatory sentences for any crime, we are not
                                                                       2

the appropriate branch to change the sentence.   If we are to do

so, we violate art. 30 of the Massachusetts Declaration of

Rights, the separation of powers doctrine.

    I fully agree with the principal arguments outlined in

Justice Lowy's dissent, ante; namely, it is the Legislature, not

the judiciary, that prescribes punishment, Opinions of the

Justices, 378 Mass. 822, 830 & n.7 (1979), and the Legislature's

choice of punishment for adults convicted of murder in the first

degree, i.e., imprisonment for life without the possibility of

parole, is not so disproportionate to the offense as to rise to

the level of cruel or unusual punishment under art. 26.     See

G. L. c. 127, § 133A (parole eligibility disallowed for those

"serving a life sentence for murder in the first degree who had

attained the age of [eighteen] years" at time of crime);

Diatchenko v. District Attorney for the Suffolk Dist., 466 Mass.

655, 669 (2013) (Diatchenko I), S.C., 471 Mass. 12 (2015).        In

addition, I agree that the tripartite analysis for

proportionality, as adopted in Commonwealth v. Jackson, 369

Mass. 904, 910 (1976), is the proper framework for evaluating

categorical challenges to a sentencing scheme.   See Commonwealth

v. Concepcion, 487 Mass. 77, 86, cert. denied, 142 S. Ct. 408

(2021), quoting Cepulonis v. Commonwealth, 384 Mass. 495, 497-

498 (1981) (determination whether sentence is disproportionate

to crime requires "[1] an 'inquiry into the nature of the
                                                                   3

offense and the offender in light of the degree of harm to

society,' [2] 'a comparison between the sentence imposed here

and punishments prescribed for the commission of more serious

crimes in the Commonwealth,' and [3] 'a comparison of the

challenged penalty with the penalties prescribed for the same

offense in other jurisdictions'").

     Indeed, the virtue of the tripartite analysis is that it is

flexible enough to accommodate "softer," offender-specific

considerations, see Commonwealth v. Perez, 477 Mass. 677, 684-

685 (2017), S.C., 480 Mass. 562 (2018), quoting Diatchenko I,

466 Mass. at 670 (factoring "diminished culpability and greater

prospects for reform" of juvenile defendant into first prong of

tripartite analysis), while offering a (mostly) objective

framework for assessing proportionality, see Opinions of the

Justices, 378 Mass. at 830 (tripartite test created to mitigate

against "the inherent subjectivity" that "shocks the conscience"

standard invariably entails).1

     1 In certain circumstances, one or more of the three prongs
may be inapt. The crime of murder in the first degree provides
an illustrative example. See Commonwealth v. LaPlante, 482
Mass. 399, 404 n.4 (2019) (case involving juvenile convicted of
multiple homicide "defies direct application of second Cepulonis
prong" because there are no "more serious crimes to which . . .
multiple homicide ought to be compared"). However, I view this
"limitation" as a useful feature. The fact that there are no
"more serious" crimes against which to compare homicide reminds
us that homicide uniquely is devastating among the offenses one
member of our society can inflict on another. See Perez, 477
Mass. at 687, quoting Graham v. Florida, 560 U.S. 48, 69 (2010)
                                                                    4

      I write separately, however, for four reasons:   first, to

note that the parties, in urging us to extend juvenile

sentencing protections to a novel subset of adults, ask us to

commandeer the job of the Legislature to fashion criminal

punishment.   Accepting such an invitation runs afoul of bedrock

principles of the separation of powers as articulated in art.

30.   See Opinions of the Justices, 378 Mass. at 830 & n.7.   See

also United States v. Davis, 139 S. Ct. 2319, 2337 (2019)

(Kavanaugh, J., dissenting) ("when we overstep our role in the

name of enforcing limits on [the Legislature], we do not uphold

the separation of powers, we transgress the separation of

powers").

      Second, it is a mistaken notion that our prior decisions in

Diatchenko I and Perez are controlling on the question of

constitutionality because those cases involved a group of

offenders already recognized by the Legislature and the United

("[t]here is a line 'between homicide and other serious violent
offenses against the individual'"). For the victims of
homicide, "[l]ife is over" and nothing left remains, Coker v.
Georgia, 433 U.S. 584, 598 (1977); for survivors, they are left
with lifelong grief and psychological damage. See Armour &
Umbreit, The Ultimate Penal Sanction and "Closure" for Survivors
of Homicide Victims, 91 Marq. L. Rev. 381, 381 (2007) ("Studies
of family members of homicide victims found that sixty-six
percent could not find meaning after five years"). This
limitation of the second prong relative to homicide should be
viewed as prophylactic, in the sense that it cautions judges
against the contemporary impulse to lessen the consequences for
violators of society's greatest crime.
                                                                    5

States Supreme Court, Miller v. Alabama, 567 U.S. 440 (2012), as

constitutionally set apart from other offenders.   See Diatchenko

I, 466 Mass. at 670-671 (all sentences of life without

possibility of parole for juvenile offenders violate art. 26).

See also Perez, 477 Mass. at 686 (juvenile's aggregate sentence

for nonmurder offenses prior to parole eligibility is

"presumptively disproportionate" if it "exceed[s] that

applicable to a juvenile . . . convicted of murder").

    Third, I write to call attention to the inherent

capriciousness of judicial line drawing; particularly where, as

here, the court follows the neuroscience only as far as to

extend juvenile sentencing privileges to one class of adult

offenders, i.e., those from age eighteen to twenty at the time

of the offense, while omitting another tranche of adults that

the developmental science says also is deserving of protection.

See E.S. Scott & L. Steinberg, Rethinking Juvenile Justice 208,

238 (2008) ("studies of brain development indicate that

continued maturation takes place until at least age twenty-five

or so" [emphasis added]).

    Fourth and last, I write to illustrate that arbitrary

reliance on developmental neuroscience, as proposed infra,

raises troubling, if unintended, implications for other groups
                                                                    6

exposed to our criminal laws.2    By depicting the effect that such

application of the science might have on these groups, I hope to

highlight the perils that can come from judges believing that

they are following "the science," wherever it may lead.

     1.   Separation of powers.   Article 30 is unique in that it

is more explicit than the Federal Constitution in calling for

the separation of the powers of the three branches of

government.   Edwards v. Commonwealth, 488 Mass. 555, 567 (2021).

Article 30 provides:

     "In the government of this [C]ommonwealth, the legislative
     department shall never excise the executive and judicial
     powers, or either of them: the executive shall never
     exercise the legislative and judicial powers, or either of
     them; the judicial shall never exercise the legislative and

     2 Specifically, the court's application of the science, as
advanced by the parties, (1) reinforces unfair (and oftentimes
unnecessary) distinctions between older and younger offenders;
(2) raises serious questions about the rights of mature
juveniles, in addition to adults from age eighteen to twenty, to
make decisions about their health care and reproduction, see
Maroney, The False Promise of Adolescent Brain Science in
Juvenile Justice, 85 Notre Dame L. Rev. 89, 103-107, 118 (2009)
(describing well-intentioned use of brain imaging studies by
advocates to argue for reduced culpability and sanctions for
juvenile offenders while expressing concern that this reliance
could translate to arguments against granting autonomy to
adolescents in other areas); and (3) dispenses with any
expectation that our legal norms can influence the development
of juveniles, rather than the other way around. See Buss, What
the Law Should (And Should Not) Learn from Child Development
Research, 38 Hofstra L. Rev. 13, 52 (2009) (Buss, Child
Development) (reasoning that ways in which juveniles and young
adults "perceive their relationship with their society and their
government . . . may matter more, for the successful functioning
of our legal regime and the effective exercise of individual
rights, than their acquisition of certain higher level
capacities").
                                                                    7

     executive powers, or either of them; to the end it may be a
     government of laws and not of men."3

     In recognition of art. 30, we often have insisted on the

"scrupulous observance" of the limitations of each branch of

government.     Edwards, 488 Mass. at 567, quoting New Bedford

Standard-Times Publ. Co. v. Clerk of the Third Dist. Court of

Bristol, 377 Mass. 404, 410 (1979).     The principle of judicial

restraint that embodies art. 30 "recognizes 'the inability and

undesirability of the judiciary substituting its notions of

correct policy for that of a popularly elected Legislature.'"

Joslyn v. Chang, 445 Mass. 344, 351-352 (2005), quoting Zayre

Corp. v. Attorney Gen., 372 Mass. 423, 433 (1977).

     Here, through the use of labels, the court shapes the issue

merely as invalidating an unconstitutional statute.      Ante

at       .   In substance, however, the court circumvents the

Legislature's power and substitutes its own notions of correct

     3 In contrast, the Federal Constitution states: "All
legislative Powers herein granted shall be vested in a Congress
of the United States, which shall consist of a Senate and House
of Representatives." Art. I, § 1, of the United States
Constitution. It also vests the judicial power of the United
States "in one [S]upreme Court, and in such inferior Courts as
the Congress may from time to time ordain and establish." Art.
III, § 1, of the United States Constitution. The doctrine of
the separation of powers long has been recognized by Federal
law. See K.J. v. Superintendent of Bridgewater State Hosp., 488
Mass. 362, 367 (2021). However, unlike art. 30 of the
Massachusetts Declaration of Rights, the Federal Constitution
does not call explicitly for the separation of powers among the
three branches of government. See Gray v. Commissioner of
Revenue, 422 Mass. 666, 671 n.5 (1996).
                                                                   8

policy based on the parties' submission of ever-changing

neuroscience.   See Joslyn, 445 Mass. at 351-352.

     In drawing hard lines between juveniles and "emerging

adults,"4 and older adult offenders, the court points to

instances in which the Legislature has opted not to treat

individuals from ages eighteen through twenty-one in the same

manner that it does adults.    Ante at    .   For example, those

who are age eighteen may serve on a jury and vote.    See G. L.

c. 234A, § 4 (right to serve on jury); G. L. c. 51, § 1 (right

to vote).   But they may not gamble or purchase alcohol or

tobacco.    See G. L. c. 23K, §§ 25 (h), 43 (right to gamble);

G. L. c. 138, § 34 (right to purchase alcohol); G. L. c. 270,

§ 6 (right to purchase tobacco).

     While there are instances in which individuals from age

eighteen to twenty-one are treated differently under the law

from individuals over age twenty-one, where such a distinction

has been made, it has been made through legislative action,

i.e., the enactment of a statute.   See, e.g., G. L. c. 23K, § 43

(must be age twenty-one to gamble in Commonwealth gaming

establishment); G. L. c. 138, § 34 (must be age twenty-one to

purchase, deliver, or sell alcohol); G. L. c. 270, § 6 (must be

     4 As styled by the court and the parties, "emerging adults"
is defined as someone aged eighteen or older, but under age
twenty-one.
                                                                   9

age twenty-one to purchase tobacco).5   Neither the parties, nor

the court, have pointed to a single instance in which the

judiciary has taken it on itself to make such a distinction

between individuals in the newly minted "emerging adult"

category and adults, as it seeks to do here.6   That the court and

     5 In his concurrence, Justice Kafker invokes these "21+"
statutes to suggest that the Legislature has, effectively, set
aside "emerging adults" as a distinct legal subclass deserving
of protection. See ante at note 9 (Kafker, J., concurring) ("I
consider the Legislature's recognition of the need for
differential treatment of those eighteen to twenty in a variety
of other contexts when the legal rights in question implicate
the same distinctive characteristic at issue in this case to be
an important component of the analysis"). I reject that
inference, at least as it relates to sentencing for violent
crime. If the Legislature wishes to refine the age of majority
for sentencing young adults who have committed murder, as it has
done for entitlement to common vices, professional licensure,
etc., then it certainly knows how to do so.

     6 Justice Kafker points to the Supreme Court's decision in
Thompson v. Oklahoma, 487 U.S. 815, 838 (1988) (Eighth and
Fourteenth Amendments to United States Constitution prohibit
death penalty for defendants convicted of murder in first degree
committed while under age sixteen), as precedent for the use of
judicial fiat to extend protections to a novel subset of
individuals, based solely on age, sans any existing basis in
statute or code to do so. See ante at note 7 (Kafker, J.,
concurring) (starting with Thompson, supra, evolution of Federal
juvenile death penalty jurisprudence "involved judicial line
drawing based on age without reliance on a clearly legislatively
defined age group"). This reliance ignores, I think, two facts:
first, that the Supreme Court in Thompson, like the court today,
expressly drew its "line" to match the age of the appellant at
the time he committed the crime. See Thompson, supra
("Petitioner's counsel . . . have asked us to 'draw a line' that
would prohibit the execution of any person who was under the age
of [eighteen] at the time of the offense. Our task today,
however, is to decide the case before us . . ."). Second, it
ignores those Federal statutes and codes in place at the time of
the Thompson decision that placed fifteen year olds firmly
                                                                 10

the parties can point only to legislative action to support

their creation of this "emerging adult" category7 furthers the

position that the drawing of this line is best left to the

popularly elected Legislature.   See Zayre Corp., 372 Mass. at

443-444 (while statute may contain faults, those statutory

within the category of "juvenile," as defined by Congress. See,
e.g., id. at 851-852 (O'Connor, J., concurring in judgment)
(noting that bill recently passed by United States Senate
authorizing capital punishment for certain drug offenses, 134
Cong. Rec. 14117, 14118 [1988], "prohibit[ed] application of
[death] penalty to persons below the age of [eighteen] at the
time of the crime"); Juvenile Justice and Delinquency Prevention
Act of 1974, Pub. L. No. 93-415, 88 Stat. 1109, 1133 (1974)
(operative Federal statute concerning juvenile justice at time
of Thompson decision defined "juvenile" as "a person who has not
attained his eighteenth birthday").

     7 Such "action" extends to the Legislature's creation of the
Legislative Task Force on Emerging Adults in the Criminal
Justice System (task force) in 2018. See ante at note 22; St.
2018, c. 69, § 221. In its report, the task force concluded
that "[e]merging adults . . . in the criminal justice system are
a unique population that requires developmentally-tailored
programming and services." Emerging Adults in the Massachusetts
Criminal Justice System: Report of the Task Force on Emerging
Adults in the Criminal Justice System (Feb. 26, 2020), 2020
Senate Doc. No. 2840, at 6 (Report of the Task Force). However,
as noted by Justice Lowy, ante, any attempt to derive
contemporary standards of decency concerning mandatory life
sentences for young adults from the proposals authored by the
task force is misplaced, because the task force (i) defined
"emerging adults" as individuals from age eighteen to twenty-
four, and (ii) excluded the crime of murder from its proposed
carceral reforms. See ante at     ; Report of the Task Force,
supra at 10. Further, if the conclusion of the task force is
that the young adult prison population requires developmentally
tailored programming and services, this court is powerless to
implement such reforms, along with its reformulation of parole
eligibility for adults from age eighteen to twenty convicted of
murder.
                                                                   11

faults that fail to rise to equivalent of constitutional

infirmity are better left for Legislature to resolve).

    The proper exercise of judicial restraint and

acknowledgment of the bedrock principle of separation of powers

found in art. 30 may lead, at times, to results that feel

difficult.   See Commonwealth v. Baez, 480 Mass. 328, 332 (2018)

(no violation of art. 26 where Legislature's statutory scheme

allowed even predicate offenses that were committed when

defendant was under age eighteen to count toward enhanced

mandatory minimum sentences under Armed Career Criminal Act).

See also Commonwealth v. Guzman, 469 Mass. 492, 498 n.9 (2014)

(Legislature's decisions to limit discretion of sentencing

judges by imposition of mandatory minimum sentences does not

derogate separation of powers); Commonwealth v. Smith, 431 Mass.

417, 417-420 (2000) (art. 30 compelled dismissal of indictment

for two counts of incest, pursuant to G. L. c. 272, § 17, based

on defendant's molestation of his daughter and forcing her to

perform oral sex on him, because such conduct did not constitute

"sexual intercourse" as defined by Legislature's specific choice

of words in statute).

    Here, although much is made of neuroscience, and the fact

that this group of "emerging adults" lacks maturity and

responsibility, such that they are prone to risk taking and

negative influence from their peers, the science alone,
                                                                    12

accompanied with the Justices' personal and moral beliefs, is

not enough to take this decision away from the Legislature.

Novel discoveries about how certain areas of the brain may

function does not explain "why" and "how" we make the decisions

we make.     The human exercise of free will is the foundation of

our criminal law; it is not reducible to magnetic resonance

imaging (MRI) scans.    But, if it is so reducible, then that is

something over which the citizens and their representatives

should engage in vigorous debate.     The capacity for change and

reform for the individuals that fit in this "emerging adult"

category also does not tip the scale, as it is difficult to

conclude that any human being is incapable of change and reform,

regardless of his or her age.     See Commonwealth v. O'Neal, 369

Mass. 242, 273 (1975) (Tauro, C.J., concurring) ("The great

responsibility of a judge is to exercise his [or her] best

judgment in applying his [or her] interpretation of the law to

the facts.     No judge should ever be concerned with whether his

[or her] decision will be popular or unpopular. . . .

[P]olitical considerations of the day, contemporary public

emotions [no matter what their motivation], and personal

philosophies are completely foreign and irrelevant to the

exercise of [a judge's] judicial power.     This is the very

essence of judicial duty -- no less should be given and no more

should be required").
                                                                    13

    Therefore, where contemporary personal and moral beliefs

may lend themselves toward the opposite result, the express

limitations placed on the judiciary under art. 30 constrain us

from making the determination that abolition of sentences of

life without the possibility of parole for individuals from age

eighteen to twenty-one in this "emerging adult" category is

appropriate.    See Baez, 480 Mass. at 332-333 (Gants, C.J.,

concurring) (acknowledging Legislature's power to impose

mandatory minimum sentences, while also encouraging Legislature

to reconsider wisdom and fairness of statutory scheme that

allows predicate offenses, committed when defendant was

juvenile, to count toward enhanced mandatory minimum sentences

under Armed Career Criminal Act).    While scrupulous observation

of these limitations sometimes may be difficult, the

constitutional principle of the separation of powers among the

branches is too fundamental to our form of government to be

disregarded on a case-by-case basis.     See Opinion of the

Justices, 365 Mass. 639, 640-641 (1974).

    2.   Diatchenko I and Perez do not control the issue

presented.     In addition to our long-standing jurisprudence under

art. 30, which mandates the separation of powers in instances

such as this, it is necessary to write separately to emphasize

that neither Diatchenko I nor Perez binds us in any manner on

the constitutionality of the punishment in question.
                                                                  14

    As already outlined extensively and carefully in Justice

Lowy's dissenting opinion, ante, our holding in Diatchenko I,

466 Mass. at 658, was limited expressly to "individuals who were

under the age of eighteen when they committed the crime of

murder in the first degree."   The Legislature already had

determined which individuals were juveniles.   In Diatchenko I,

we concluded that mandatory sentences of life without parole for

juvenile offenders were disproportionate under art. 26.      Id. at

658-659.   Importantly, we limited our proportionality analysis

only to juvenile offenders, i.e., those "defendants who were

under the age of eighteen at the time they committed murder in

the first degree," because juvenile offenders constituted a

group of individuals already extensively recognized by the

Legislature as a group in need of protections different from

those afforded to the average offender.   See id. at 658 n.8,

citing G. L. c. 119, § 72B.    See also G. L. c. 119, §§ 52-74

(delinquency determination and procedures set forth by

Legislature).   In Diatchenko I, we used neuroscience, social

science, and contemporary standards of social norms, as did the

Supreme Court in Miller, 567 U.S. 440, to operate within those

already-defined age parameters created by the Legislature and

held that the continued practice of sentencing juvenile

offenders to life without the possibility of parole for murder
                                                                  15

in the first degree violated the protections of art. 26.

Diatchenko I, supra at 660, citing Miller, supra at 471.

    The same is true for our decision in Perez.    In Perez, 477

Mass. at 679, we held "that where a juvenile is sentenced for a

nonmurder offense or offenses, and the aggregate time to be

served prior to parole eligibility exceeds that applicable to a

juvenile convicted of murder, the sentence cannot be reconciled

with art. 26 unless, after a hearing on the factors articulated

in Miller[, 567 U.S. at 477-478], the judge makes a finding that

the circumstances warrant treating the juvenile more harshly for

parole purposes than a juvenile convicted of murder" (emphasis

added).

    The decision in Perez came on the heels of our decision in

Diatchenko I, 466 Mass. 655, and involved juvenile offenders

convicted of crimes not punishable by life without the

possibility of parole who were faced with sentences that

provided for time to be served prior to parole eligibility that

exceeded the time applicable to juveniles convicted of murder in

the first degree.   Perez, 477 Mass. at 677-679.   In conducting a

proportionality analysis under art. 26, we acknowledged what we

already previously had accepted in Diatchenko I, and what the

Supreme Court already had accepted in Miller, i.e., that

"children are constitutionally different from adults for [the]
                                                                   16

purposes of sentencing."   See Perez, supra at 683, quoting

Miller, 567 U.S. at 471.

    We reiterated that "the 'unique characteristics of juvenile

offenders' should weigh more heavily in the [art. 26]

proportionality calculus" (emphasis added).      Perez, 477 Mass. at

683, quoting Diatchenko I, 466 Mass. at 671.      Such

characteristics included diminished culpability and greater

prospects for reform.   See Perez, supra at 684.     Despite our

recognition in Perez of the neuroscience that we previously

acknowledged in Diatchenko I, our holding in Perez operated

entirely within an already-defined binary set by the

Legislature, i.e., juvenile offenders and nonjuvenile offenders.

Thus, as with Diatchenko I, it is necessary to emphasize that

Perez also does not control the issue presented because it, too,

involved the category of juvenile offenders, for whom the

Legislature had provided extensive procedures and protections,

see G. L. c. 119, §§ 52-74, as opposed to the "emerging adult"

category of individuals about whom the Legislature has spoken

very little.

    3.    Arbitrary line drawing.     The court uproots the

legislatively drawn age at which an offender may be sentenced to

life without the possibility of parole for murder in the first

degree.   See G. L. c. 127, § 133A.    Perhaps nothing speaks

louder to the flaws in the court's reasoning, however, than
                                                                  17

having crafted a line that ends at age twenty-one, thereby

engaging in legislative line drawing inconsistent with the

science on which it relies.   See Icenogle et al., Adolescents'

Cognitive Capacity Reaches Adult Levels Prior to Their

Psychosocial Maturity:   Evidence for a "Maturity Gap" in a

Multinational, Cross-Sectional Sample, 43 Law & Hum. Behav. 69,

70 (2019) (neuroscientific evidence indicating that brain

development, and concomitant ability to self-regulate, continues

to develop during early twenties); Steinberg, A Social

Neuroscience Perspective on Adolescent Risk-Taking, 28

Developmental Rev. 78, 83 (2008) (self-regulatory competence for

young adults "occurs gradually and is not complete until the

mid-[twenties]"); Steinberg, The Influence of Neuroscience on

U.S. Supreme Court Decisions about Adolescents' Criminal

Culpability, 14 Nature Revs. Neurosci. 513, 515-516 (2013)

(individuals "in their early [twenties]" more likely than older

adults to engage in "risky behaviour;" seek "novel" and
                                                                  18

rewarding "sensation[s];" and possess "low" "impulse

control").8,9

     By not holding to the line drawn by the Legislature, i.e.,

eighteen, or the line drawn roughly by contemporary

neuroscience, i.e., twenty-five, the "[court]'s holding simply

replaces [one] unfairness with another."   People v. Parks, 510

Mich. 225, 287 (2022) (Clement, J., dissenting).   Defendants who

are age twenty years and 364 days at the time of their crime

would be afforded the possibility of parole; defendants who are

     8 See also United States v. Gall, 374 F. Supp. 2d 758, 762
n.2 (S.D. Iowa 2005), rev'd, 446 F.3d 884 (8th Cir. 2006),
rev'd, 552 U.S. 38 (2007) ("Recent studies on the development of
the human brain conclude that human brain development may not
become complete until the age of twenty-five"); Brain Immaturity
Could Explain Teen Crash Rate, Wash. Post, Feb. 1, 2005 (recent
National Institutes of Health study suggested "that the region
of the brain that inhibits risky behavior is not fully formed
until age [twenty-five]").

     9 Or, put differently, the court is unwilling to follow the
scientific consensus as to the age at which impulsivity, self-
regulation in an emotionally aroused state, sensation seeking,
and brain plasticity all calcify for the purposes of criminal
culpability. But see Buss, Child Development, 38 Hofstra L.
Rev. at 46 ("in the end, culpability is necessarily a legal
judgment, not a psychological one, so the suggestion that
developmental findings determine culpability is just
misleading"); Fuchs & Flügge, Adult Neuroplasticity: More Than
40 Years of Research, Neural Plasticity, May 4, 2014, at 1-2
(factors such as stress, adrenal and gonadal hormones,
neurotransmitters, growth factors, certain drugs, environmental
stimulation, learning, and aging change neuronal structures and
functions of adult brains and may induce generation of new
neurons, i.e., neurogenesis). This fails to reckon with the
naked fact that our most sacred and profane choices often emerge
from the depths of the psyche, something neuroscience has not
yet been able to map.
                                                                  19

one day older would have no such opportunity.   The court

"readily admits that the science does not support that dividing

line either."10   Id.   See ante at    ,    .

     Imposed by judicial fiat, twenty-one minus a day is not

tethered to hard science, nor is it joined to "contemporary

standards of decency" as reflected in our criminal statutes.

Good v. Commissioner of Correction, 417 Mass. 329, 335 (1994).

There appears to be no clear limiting principle,11 and as a

result, we soon would see claims arguing that we should extend

Diatchenko I protections to those aged twenty-one years (or

older) at the time of their crime.    After all, if the science

     10The science also does not conclude that female offenders
suffer the same alleged inability to control themselves.
Following the court's reasoning, girls and women should be
treated more harshly. For a full discussion of this point, see
note 24, infra.

     11The court offers no material justification for limiting
the category of "emerging adults" to those from age eighteen to
twenty other than that that is the range requested by the
defendant when his case was paired with Commonwealth v.
Robinson, 493 Mass.     (2023). Tellingly, prior to the two
cases being joined, the defendant urged twenty-two as the
appropriate age cap. While the judge's factual findings were
limited to individuals aged eighteen through twenty at the time
of commission, much of the scientific expert testimony and
studies supporting those findings included individuals twenty-
one years of age (and in some instances older) as it relates to
salient categories of neurocognitive development, e.g., "Many of
Dr. Galvan's studies included [twenty-one year olds] in the
group of 'late adolescents' who were studied"; "for purposes of
assessing the constitutionality of mandatory life-without-parole
sentences, the brain science relied upon by the Court lends some
support for treating [eighteen] through [twenty-one year olds]
differently than older persons."
                                                                   20

says that individuals at age twenty-one have all the same

psychosocial limitations as those age seventeen, then, according

to the court's reasoning, the mandatory imposition of life

without the possibility of parole also must be unconstitutional

as applied to a twenty-one year old.   Such are the consequences

when an appellate court invokes science selectively to achieve a

policy outcome while "ignor[ing] the possibility that the age of

majority is based less on scientific exactitude, and more on

'society's judgments about maturity and responsibility.'"

Matter of the Personal Restraint of Monschke, 197 Wash. 2d 305,

332 (2021) (Owens, J., dissenting), quoting Davis v. Department

of Licensing, 137 Wash. 2d 957, 974 (1999).

    Cognizant that any line drawn by the court in this matter

would be, by definition, "both overinclusive and

underinclusive," the remedy proposed by the parties simply is

overbroad.   Parks, 510 Mich. at 275 (Bernstein, J., concurring),

citing Roper v. Simmons, 543 U.S. 551 (2005).   Until today, no

court in the country has imposed a blanket prohibition on

nondiscretionary sentences of life without parole for adults

over age eighteen but under age twenty-one who have been

convicted of murder.   See Parks, supra at 244-245 (requiring

trial judge to conduct individualized sentencing hearing for

convicted murderers who killed while they were eighteen years of

age prior to imposing life sentence); Matter of the Personal
                                                                  21

Restraint of Monschke, 197 Wash. 2d at 324-325 (same, but

includes those from ages nineteen to twenty).   When we are

called on to remedy "constitutional infirmity,"12 be it in a

statute, procedural practice, or rule, the principles of

judicial restraint mandate that we dispassionately remove the

offending part while leaving the nonoffending whole as intact as

possible, as a surgeon would.   Zayre Corp., 372 Mass. at 444.

See Ramirez v. Commonwealth, 479 Mass. 331, 338 (2018), quoting

Ayotte v. Planned Parenthood of N. New England, 546 U.S. 320,

329 (2006) (in "confronting a constitutional flaw in a statute,

. . . a court 'should try not to nullify more of a legislature's

work than is necessary'").   See, e.g., Herrmann v. Attorney

Gen., 492 Mass. 51, 59 (2023); Planned Parenthood League of

Mass., Inc. v. Attorney Gen., 424 Mass. 586, 603 (1997) (Lynch,

J., dissenting) ("striking down a statute as unconstitutional is

a dramatic exercise of judicial power to be used sparingly").

That the defendant barely entertains individualized sentencing

hearings as a less drastic remedy demonstrates that he is in

     12In this case, the alleged infirmity is that portion of
G. L. c. 265, § 2, as amended through St. 1982, c. 554, § 3,
that sets forth the penalty for murder in the first degree and
distinguishes between the penalties for adults and juveniles.
See Commonwealth v. Watt, 484 Mass. 742, 754-756 (2020). Also
affected is that portion of the parole statute, G. L. c. 127,
§ 133A, that denies parole to those from age eighteen to twenty.
                                                                    22

search of a movement court.13,14   We would be wise to reject his

invitation.

     13I am not suggesting that this court should, in lieu of a
blanket ban on the sentence, require that judges conduct an
individualized hearing before imposing life without the
possibility of parole for adults from ages eighteen through
twenty convicted of murder in the first degree. Both outcomes,
as discussed supra, wrest power impermissibly from the
Legislature. I do, however, respect that other appellate
courts, contemplating the same alleged violation of their
respective constitutions, trust their trial judges to weigh the
developmental neuroscience and make the correct call. See
Parks, 510 Mich. at 244 ("Michigan Constitution requires that
[young adults] convicted of first-degree murder receive the same
individualized sentencing procedure . . . as juveniles who have
committed first-degree murder"); Matter of the Personal
Restraint of Monschke, 197 Wash. 2d at 311 (State constitutional
bar against "cruel punishment" requires "courts to exercise
complete discretion to consider mitigating circumstances
associated with the youth of any juvenile defendant, even when
faced with mandatory statutory language" [citation and quotation
omitted]). See, e.g., United States v. Gonzalez, 981 F.3d 11,
22 (1st Cir. 2020), cert. denied, 141 S. Ct. 1710 (2021)
(Miller, 567 U.S. at 480, stands for proposition that "so long
as the defendant's youth is taken account in the sentencing
process, a sentencer's ability to impose a life-without-parole
sentence is not foreclosed" [citation, quotations, and
alterations omitted]).

     14Subject to the rules of evidence, there is nothing that
prevents the defense from offering the above research on
neurodevelopmental science to the jury at trial. Indeed, in a
murder trial, it is the job of the "jurors [to] find the facts,
including those facts or issues on which they hear psychiatric
testimony," such as the defendant's mental capacity at the time
of the killing or whether he lacked the criminal responsibility
for murder. Commonwealth v. Gould, 380 Mass. 672, 679 (1980).
See Commonwealth v. Muller, 477 Mass. 415, 431 (2017)
(Commonwealth must prove criminal responsibility beyond
reasonable doubt); Commonwealth v. Oliveira, 445 Mass. 837, 848-
849 (2006) ("reduced mental capacity is relevant to the jury's
exercise of their broad discretion as a reflection of the
community's conscience"). Given that the research relied on by
the court raises concomitant issues of control, agency, and
                                                                 23

     One additional point -- the age-crime curve is one of the

most well-known graphs in criminology.   It shows, in relevant

part, that the male "rate of offending by age rises in

midadolescence, peaks in the later teen years,"15 and begins

dropping precipitously "around age twenty," and "[b]y the

midtwenties, the rate of offending for most crimes is much

lower" (footnotes omitted).   Buss, Kids Are Not So Different:

The Path from Juvenile Exceptionalism to Prison Abolition, 89 U.

Chi. L. Rev. 843, 879-880 (2022) (Buss, Juvenile

Exceptionalism).   Put another way, the age-crime curve

demonstrates that most offenders stop offending somewhere from

culpability, it is perfectly reasonable to put such research
before the collective wisdom of the jury to consider in
determining whether to render a verdict of murder in the first
or second degree, manslaughter, or not guilty. See Commonwealth
v. Philyaw, 55 Mass. App. Ct. 730, 737 (2002), quoting United
States v. McKinney, 429 F.2d 1019, 1023 (5th Cir.), modified on
rehearing, 434 F.2d 831 (1970), cert. denied, 401 U.S. 922
(1971) (jury may "leaven [their] deliberations with [their]
wisdom and experience" so long as jury do not "bring extra facts
into the jury room").

     15It is well known, and not controversial to state, that
males commit much more crime than females. See Federal Bureau
of Investigation, Criminal Justice Information Services
Division, 2019 Crime in the United States, https://ucr.fbi.gov
/crime-in-the-u.s/2019/crime-in-the-u.s.-2019/tables/table-
42/table-42.xls [https://perma.cc/HA49-KT7W] (in 2019, men
accounted for ninety-seven percent of persons arrested for
murder, ninety-three percent of persons arrest for sex offenses,
eighty-eight percent of persons arrested for murder and
nonnegligent manslaughter, seventy-nine percent of persons
arrested for other violent crimes, and sixty-two percent of
persons arrested for property crimes).
                                                                     24

age eighteen to twenty-five.   See id. at 880; Farrington,

Loeber, & Howell, Young Adult Offenders:    The Need for More

Effective Legislative Options and Justice Processing, 11

Criminology & Pub. Pol'y 729, 734-735 (2012) ("highest

concentration of desistance takes place during early adulthood

irrespective of age of [first crime]").

    There are many theories regarding why criminal desistance

occurs in early adulthood.   Social scientists, however,

generally accept that youthful offenders stop offending

primarily because they have attained full psychosocial maturity

and have begun to assume adult roles.     Buss, Juvenile

Exceptionalism, 89 U. Chi. L. Rev. at 880.      If the court is to

take the drastic step of departing from the statutory age of

majority in favor of following the purported science, then it

should at least be bold enough to follow the science whole

cloth.   In a typically developing individual in our culture,

"[b]rain and behavioral maturation continues . . . until roughly

[age] twenty-five"; therefore, extending the protections of

Diatchenko I to this age at least would "be consistent with the

[c]ourt's developmental logic."   Id. at 881.     That the court

presses no further than age twenty reflects two things:

justified unease with extending youthful offender protections to

what will be, for most violent criminals, the lifespan of their
                                                                  25

criminal careers;16 and more important, tacit recognition that it

should be "up to the Legislature to balance the science with

society's penological goals."   Parks, 510 Mich. at 299 (Clement,

J., dissenting).   See Gregg v. Georgia, 428 U.S. 153, 174–175

(1976) ("while [appellate courts] have an obligation to insure

that constitutional bounds are not overreached, we may not act

as judges as we might as legislators"); Jackson, 369 Mass. at

909, quoting Weems v. United States, 217 U.S. 349, 379 (1910)

(basic functions of Legislature, such as proscribing punishment,

"not to be interfered with lightly, nor by any judicial

conception of their wisdom or propriety").

     4.   Unintended consequences.   In arguing that art. 26

forbids the imposition of a sentence of life without parole for

adults from ages eighteen through twenty, the court and the

defendant rely heavily on four core factual findings made by the

judge, namely, that young adults, in relation to their older

peers, (i) demonstrate less impulse control; (ii) are more prone

to risk taking in pursuit of rewards; (iii) are more susceptible

to peer influence; and (iv) have greater capacity for change

     16See Garrett, Seal-Carlisle, Modjadidi, & Renbeg, Life
Without Parole Sentencing in North Carolina, 99 N.C. L. Rev.
279, 286 (2021) (data associated with commission of crime
reveals high correlation between criminality and age, "with
[twenty-five] years of age considered the peak of one's criminal
career").
                                                                    26

owing to the plasticity of their brains.17     See ante at    .    The

fourth finding has immense import; it is young adults'

neuroplasticity that warranted the extension of Diatchenko I and

ruled out individualized sentencing hearings.     See ante

at        (Kafker, J., concurring).   See also Diatchenko I, 466

Mass. at 670, citing Graham v. Florida, 560 U.S. 48, 68 (2010)

("Simply put, because the brain of [an 'emerging adult'] is not

fully developed, either structurally or functionally, by the age

of [twenty-one], a judge cannot find with confidence that a

particular offender, at that point in time, is irretrievably

depraved").

     17The novel technology relied on by the court and the
parties (e.g., structural MRIs [sMRIs] and functional MRIs
[fMRIs]) may explain why young men possess a greater biological
proclivity to commit violent crimes. I note, however, that
scant research exists on the effect that committing violent
crimes -- murder, in particular -- has on brain development in
juveniles and young adults. Most of the research on murder and
the young brain either (i) focuses causally on the decision to
kill, see Cope et al., Abnormal Brain Structure in Youth Who
Commit Homicide, Neuroimage: Clinical, vol. 4, 2014, at 800-801
(MRI data comparing adolescent homicide offenders to
incarcerated adolescents who did not commit homicide showed
reduced gray matter volumes in medial and lateral temporal lobes
in adult offenders); or (ii) traces the parts of the brain most
active during the act of killing, see Molenberghs et al., The
Neural Correlates of Justified and Unjustified Killing: An fMRI
Study, 10 Soc. Cognitive & Affective Neurosci. 1397, 1397 (2015)
(activation found in lateral orbitofrontal cortex during
simulation where participants were made to watch first-person
perspective animated video recordings in which they imagined
themselves to be shooting innocent civilians).
                                                                  27

     I accept, as I must unless they clearly are erroneous, the

judge's factual findings relating to neurocognitive development

in young adults.   Moreover, while I disagree with the result

reached by the court, I accept that it engaged in a good-faith

proportionality analysis in relation to the science and social

science credited at hearing.   See, e.g., Diatchenko I, 466 Mass.

at 660-661, 669 (art. 26 proportionality analysis requires court

to consider science, social science, contemporary standards of

decency, law of other States, and "common sense").18   Having said

that, I believe the court's application of the neuroscience to

eighteen through twenty year olds, particularly as it relates to

brain plasticity, is short-sighted and has corresponding

implications for populations that the court did not consider,

     18Arguably, Diatchenko I also violates art. 30. By
removing the judge's ability to weigh particularly heinous
factors in capital cases, the court went much further,
unnecessarily so, than the Supreme Court required in Miller.
See, e.g., Commonwealth v. O'Brien, 432 Mass. 578, 592 (2000)
(juvenile tried as adult sentenced to life without parole in
connection with murder of mother of close friend, who was
stabbed ninety-eight times); Commonwealth v. Berry, 420 Mass.
95, 114 (1995) (life sentence affirmed for juvenile convicted of
breaking into apartment and murdering eighty-seven year old
widow with butcher knife in her sleep); Commonwealth v.
LaPlante, 416 Mass. 433, 444 (1993), S.C., 482 Mass. 399 (2019)
(life sentence affirmed for juvenile convicted of raping and
killing pregnant mother and drowning her two children).
                                                                      28

i.e., older adult offenders,19 mature minors,20 and at-risk

juveniles.    I address each group in turn.

     a.    Older offenders.   The goals of sentencing a convicted

criminal to a term of confinement include "punishment,

deterrence, incapacitation, and rehabilitation."      Commonwealth

v. McIntyre, 436 Mass. 829, 833 (2002), citing Commonwealth v.

Power, 420 Mass. 410, 414 (1995), cert. denied, 516 U.S. 1042

(1996).    When judges impose sentences, they strive "to penalize

offenders in such a way that they understand the reasonableness

of the punishment, 'free of any legitimate hatred for the system

that punished [them], and without the unnecessary venom we

generate by excessive [punishment].'"     McIntyre, supra at 834,

quoting Nygaard, On the Philosophy of Sentencing:     Or, Why

Punish?, 5 Widener J. Pub. L. 237, 266 (1996).

     As noted supra, the court relies heavily on research on

brain plasticity, and its persistence into an individual's

twenties, to hold that a sentence of mandatory life without

parole for adults from ages eighteen through twenty violates

art. 26.     See Diatchenko I, 466 Mass. at 669.   Properly framed,

however, their principal reason for concluding that eighteen

through twenty year olds deserve better treatment at sentencing

     19I.e., those offenders ages twenty-five and older at the
time of their crime (older offenders).

     20   Females, in particular.
                                                                    29

"is also, by implication, an account of why [older] adults [do

not]."      Buss, Juvenile Exceptionalism, 89 U. Chi. L. Rev. at

882.

       Invoking the science of neuroplasticity to extend

Diatchenko I protections to "emerging adults" signals that older

offenders, sapped of their neurological capacity for change, are

incarcerated primarily for punishment and societal deterrence.

By contrast, the jailing of offenders who are from ages eighteen

to twenty or juveniles at the time of their crimes, whose brains

have yet to calcify, sounds squarely in rehabilitation.21     See

Buss, Juvenile Exceptionalism, 89 U. Chi. L. Rev. at 883

(concern that "[t]he more that special qualities and treatment

are identified and justified for [an] exceptionalist group

[i.e., "emerging adults" and juvenile offenders], the more the

unexceptional group [i.e., older offenders] is defined by their

lack of these qualities and their disqualification from special

treatment").     This dichotomy entrenches needlessly the

distinctions between older offenders, on one end, and juveniles

and young adults, on the other.     Worse still, it may be

considered biological fatalism that is plainly at odds with the

data on recidivism, which shows that juvenile prisoners, once

       This necessarily raises ethical questions about whether
       21

society can claim rehabilitation as a justification for jailing
any criminal beyond age twenty-five.
                                                                    30

released, reoffend at a rate higher than their adult peers.       See

K. Wade et al., Wisconsin Legislative Audit Bureau, Report 08-3,

A Review:   17-Year-Old Offenders in the Adult Criminal Justice

System, Department of Correction, at 7 (Feb. 2008) (seventeen

year old offenders subject to adult jurisdiction were

reincarcerated more often than adult offenders); Woolard et al.,

Juveniles within Adult Correctional Settings:    Legal Pathways

and Developmental Considerations, Int'l J. Forensic Mental

Health, vol. 4, 2005, at 7 (compilation of statistics from

fifteen States indicate that juveniles released from State

prisons are rearrested at rate sixteen percent higher than adult

counterparts).    Moreover, I conclude that such fatalism toward

adult offenders contradicts a central precept of our criminal

justice system:    that we are not only our worst act and,

consequently, every offender has the capacity to change

regardless of the age at which he or she offended.22

     22Arguably, deterrence and public protection are important
sentencing considerations, as they are necessary for a stable,
peaceful society. It may be impossible to know whether a person
has changed; thus, I would not second-guess the Legislature's
policy choices in this area. There may be a point, however, at
which the Legislature determines that there is no need for
deterrence or public protection at a certain age. This is not a
determination for the court unless the Legislature amends the
sentence for murder and provides judges with the mandate to
craft the most appropriate term of years in the unique
circumstances of the case. See, e.g., Conn. Gen. Stat. §§ 53a-
35a, 53a-45 (class A felony of murder punishable by "a term not
less than twenty-five years nor more than life"); D.C. Code
§ 22–2104 (sentence for "murder in the first degree shall be not
                                                                   31

    Finally, the court's unwieldy application of neurocognitive

science threatens to exacerbate further differences in how we

sentence juveniles and how we sentence older offenders.     More

specifically, the sentencing provisions governing juveniles are

grounded on "increasingly sophisticated social-scientific

understandings" of their capacity, whereas the sentencing

provisions for older offenders take no account of those factors.

Buss, What the Law Should (And Should Not) Learn from Child

Development Research, 38 Hofstra L. Rev. 13, 42 (2009) (Buss,

Child Development).   Cf. Strough & Bruine de Bruin, Decision

Making Across Adulthood, Annual Rev. of Developmental Psychol.,

vol. 2, 2020, at 357 ("Age-related declines in fluid reasoning

ability and working memory can compromise the quality of older

adults' decision making when decisions are complex").

    b.    Mature juveniles.   Relative to other States,

Massachusetts law affords minors some autonomy to consent to

well-counseled treatment for their physical and mental health

care.    See Baird v. Attorney Gen., 371 Mass. 741, 754 (1977)

(recognizing "mature minor" rule in Commonwealth for

nonemergency medical treatment where [1] best interests of minor

are served by not notifying parents of intended medical

less than [thirty] years nor more than life imprisonment without
release"); 730 Ill. Comp. Stat. 5/5-4.5-20 (providing for
sentence of "not less than [twenty] years and not more than
[sixty] years" for murder in first degree).
                                                                  32

treatment and [2] minor can give informed consent to that

treatment); G. L. c. 123, § 10 (minors aged sixteen or seventeen

may consent to admission at mental health treatment facility);

104 Code Mass. Regs. § 25.03 (2016) (clarifying that mental

health providers may, pursuant to Massachusetts's "mature minor"

rule, elect to provide mental health treatment without notifying

minor's parents).   This autonomy encompasses the ability of

certain minors to control their sexual health and reproduction,

see G. L. c. 111, § 24E (enabling sexually active minors of

childbearing age access to family planning services offered

through Department of Public Health); G. L. c. 112, § 12F (same,

but for treatment of human immunodeficiency virus and enumerated

sexually transmitted diseases), and, if desired, avail

themselves of the protections provided by the so-called "ROE

Act" to terminate a pregnancy, see G. L. c. 112, § 12R

(permitting abortion procedure for patients sixteen and older on

obtaining patient's written informed consent).

    In short, it is Commonwealth policy to respect, through

legislation, the capacity of late adolescents to make certain

decisions regarding their physical and mental health as well as

their bodily autonomy.   In reaching its conclusion, however, the

court applies neuroscience selectively to argue that our

youngest adults, to say nothing of teenagers, are not fully
                                                                  33

capable of discerning basic right from wrong.23   I reject that

inference.

     The application of cognitive neuroscience to, in essence,

infantilize young adults as a class undercuts the collective

wisdom of the Commonwealth, which clearly favors trusting young

people with decisions of (even) life-altering import.   Of more

concern, the court's paternalism "rais[es] troubling questions

about" the rights of adolescents, girls in particular,24 "to make

     23See Wagland & Bussey, Appreciating the Wrongfulness of
Criminal Conduct: Implications for the Age of Criminal
Responsibility, 22 Legal & Crim. Psychol. 130, 130 (2017) (eight
year olds demonstrated that they were just as likely as older
children and adults to understand wrongfulness of criminal
behavior and be able to distinguish criminal behavior from
mischievous behavior).

     24Indeed, the court's and the parties' yoking of
neurodevelopmental science to abstract notions of culpability
and redeemability, taken to its logical extent, would have
disparate impact on the sentencing of girls, who mature faster
than boys "in many respects relevant to [the] law." Buss, Child
Development, 38 Hofstra L. Rev. at 40. See L. Brizendine, The
Female Brain 44 (2006) (claiming that biological differences
between males and females result in females maturing two or
three years earlier); Cauffman & Steinberg, (Im)maturity of
Judgment in Adolescence: Why Adolescents May Be Less Culpable
than Adults, 18 Behav. Sci. & L. 741, 753, 758 (2000) (females
exhibit greater psychosocial maturity than males). My
colleagues in the majority likely would bristle at the
suggestion that girls, owing to their psychosocial "head start,"
warrant a harsher punishment than boys of the same age who
commit the same crime. See, e.g., Dahl, Adolescent Brain
Development: A Period of Vulnerabilities and Opportunities,
1021 Annals N.Y. Acad. Sci. 1, 12-16 (2004) (studies show
"significant positive correlation between pubertal maturation
and sensation seeking" in both boys and girls, which is
associated with greater risk-taking behaviors). Yet if age is
the best proxy for determining whether someone has the
                                                                      34

medical decisions or decisions about [their] sexual health."

Berk, Children, Development, and the Troubled Foundations of

Miller v. Alabama, 44 L. & Soc. Inquiry 752, 759 (Aug. 2019)

(Berk, Troubled Foundations).       By invoking neuroscience to treat

young adults as a separate constitutional class, we invariably

call into question "a variety of domains concerning the choices

of young people."     Id. at 760.    See Maroney, The False Promise

of Adolescent Brain Science in Juvenile Justice, 85 Notre Dame

L. Rev. 89, 159 (2009) ("Undue emphasis on the immature brain

also might alter our societal commitment to allow teens

incrementally greater control over important aspects of their

lives," such as whether to access reproductive and sexual health

services unilaterally).    The court may attempt to confine its

analysis to the criminal sphere, but it is unclear why the

application should remain so limited.       Berk, Troubled

Foundations, supra.

    The public's trust in the capacity of our adolescents and

young adults to make certain decisions regarding their health

care has been codified into law by our representative

Legislature.   See, e.g., G. L. c. 112, § 12R; G. L. c. 123,

§ 10; G. L. c. 111, § 24E.    I would not overrule that collective

neurological capacity for change, then surely any factor that is
highly correlated with "brain age" and maturation, such as
biological sex, also is relevant.
                                                                     35

wisdom which holds "emerging adults" fully to account for their

decision to commit murder.     See G. L. c. 127, § 133A (excluding

convicted murderers aged eighteen or older at time of crime from

statutory right to parole).     See, e.g., Opinions of the

Justices, 378 Mass. at 830 (judgment of Legislature to prescribe

appropriate penalties must be "accorded due respect" by this

court).

    c.    At-risk juveniles.    Connecting the line of cases from

the Supreme Court's decision in Roper, 543 U.S. at 569-570, to

the court's decision today is the question how, precisely,

should the science of brain development affect the law.      See id.

at 569, quoting Johnson v. Texas, 509 U.S. 350, 367 (1993) ("as

any parent knows and as the scientific and sociological studies

. . . tend to confirm, '[a] lack of maturity and an

underdeveloped sense of responsibility are found in youth more

often than in adults'").     Modern neuroscience, weighed properly,

is an important, albeit supplementary, factor in our art. 26

analysis for disproportionate punishment.     See Perez, 477 Mass.

at 686; Diatchenko I, 466 Mass. at 671.     See also Miller, 567

U.S. at 471.   I do, however, question whether our focus should

be less on the extent to which our knowledge of brain

development should influence the law, and more on how knowledge

of the law ultimately may have an impact on development.      See
                                                                   36

Buss, Child Development, 38 Hofstra L. Rev. at 48 (reciprocal

relationship exists between childhood development and law).25

     Children in Massachusetts know that their legal rights and

responsibilities forever are altered on turning eighteen.

Indeed, knowledge of this situation becomes largely unavoidable

for adolescents in the years leading up to their eighteenth

birthday.   See G. L. c. 149, §§ 86, 89 (employers required to

have youth employment permits on file for all workers fourteen

to seventeen); G. L. c. 90, § 8B (must be sixteen years old to

apply for learner's permit); G. L. c. 69, § 1D (requiring

passing score on Massachusetts comprehensive assessment system,

administered in tenth grade, as prerequisite for graduation).

In short, they are on notice.   On reaching our age of majority,

adults in Massachusetts inherit the largest bundle of rights

     25Courts have been led astray by the appeal of following
what, at the time, appeared to be science. The examples are
numerous, and we are familiar with some of the more egregious
examples here in the Commonwealth. See Commonwealth v. Kater,
409 Mass. 433, 447-448 (1991), S.C., 412 Mass. 800 (1992) and
432 Mass. 404 (2000) (testimony aided in whole or in part by
hypnosis no longer admissible "because it is unreliable"). See
also Commonwealth v. Coutu, 88 Mass. App. Ct. 686, 694 n.4
(2015) (spectral evidence used to convict defendants at Salem
witch trials). I am not equating modern neuroscience with
hypnosis or spectral evidence. Rather, I note that our
understanding of this area of science is far from complete,
especially in that murky area where reflexive action ends and
our (distinctly) human choice to act originates. Using
neurodevelopmental science to assess culpability risks ignoring
hundreds of years of philosophy as well as learning from other
societal structures.
                                                                   37

they ever will receive;26 conversely, they know that they also

are exposed to the full consequences of their criminal acts in

adult courts.27

     As a court, we must be careful not to disregard the

developmental impact that this knowledge has in "nudging"

children in the direction of "that unrealized adult ideal."

Buss, Child Development, 38 Hofstra L. Rev. at 15.   See Berk,

Troubled Foundations, 44 L. & Soc. Inquiry at 765-766 ("If age

is understood not simply as a 'gross proxy,' . . . but as

marking the boundary of a democratic pre-commitment to care for

young people, it is easier . . . to justify drawing a firm line

at eighteen or establish . . . consistency [with] the mature

minor doctrine").   It is easy to shift the line in deference to

what the latest science tells us; harder still is accepting that

the present line, though imperfect, serves an aspirational

function separate and apart from being simply "the point where

     26See, e.g., G. L. c. 231, § 85O (must be age eighteen to
be party to binding and enforceable contracts); G. L. c. 234A,
§ 4 (must be age eighteen to sit on jury); G. L. c. 10, § 29
(must be age eighteen to purchase lottery ticket); and G. L.
c. 159A, § 9 (must be age eighteen to drive common carrier motor
vehicle).

     27I recognize, of course, that certain charges against
juveniles are mandated by statute to be tried in the Superior
Court rather than the Juvenile Court. See, e.g., G. L. c. 119,
§ 74, as amended through St. 2013, c. 84, §§ 25-26 (charges of
murder in first or second degree against person from ages
fourteen through seventeen must be brought in Superior Court).
                                                                  38

society draws the line for many purposes between childhood and

adulthood."   Roper, 543 U.S. at 574.   How we expose young people

to our law matters; we inhibit their growth as citizens when we

treat the law as an abstract, malevolent force from which they

require protection, rather than as those wise restraints that

make us all more free.

    5.   Conclusion.     For all the reasons stated herein, and for

all the reasons cited in Justice Lowy's dissent, ante, a

sentence of life without the possibility of parole for adults

aged eighteen to twenty does not constitute cruel or unusual

punishment under art. 26 of our Declaration of Rights.    I

respectfully dissent.