October 12, 2014

Draft

PRESENTATION OF EXPERT TESTIMONY

POLICIES

1. Experts should be asked to identify and explain the theoretical and

factual basis for any conclusion and the reasoning on which the conclusion is

based — and any limitations of their conclusions.

2. Experts should present testimony in a manner that accurately and fairly

conveys the significance of their conclusions, avoiding unexplained or undefined

technical terms or words of art.

3. Experts should remain neutral, and attorneys should respect this

neutrality. 

4. Experts should not testify beyond their expertise and should also 

appreciate the difference between testimony that the witness may give as an expert

and testimony that the same witness may give as a lay/fact witness.1 

5. Experts should not testify on direct or redirect examination concerning

case-specific conclusions not contained in the report(s)/documentation submitted

in discovery — unless in fair response to issues raised on cross-examination. If an

expert changes his or her opinion, a supplementary report should be submitted

except where the change is occasioned by new information, presented during

testimony and not previously available to the witness.

6. Experts should not testify concerning conclusions that are beyond the

limits of a laboratory’s testing protocols.

7. Experts should not use invalid or problematic terms in their reports or

when testifying.2

1 The same witness may provide testimony as both an expert or a lay witness. The

two roles need to be distinguished. The Federal Rules do “not distinguish between expert and lay

witnesses, but rather between expert and lay testimony. Certainly it is possible for the same

witness to provide both lay and expert testimony in a single case.” FED. R. EVID. 701 advisory

committee’s note (2000).

2 For example: “to the exclusion of all others” and “reasonable scientific

certainty.” These terms are discussed below. Jurisdictions that require the phrase “reasonable

scientific (or medical) certainty” should reconsider its use.

1
8. Experts should not use misleading terms3

 that suggest that the

methodology or the expert is infallible when testifying.4

9. Experts should not use potentially misleading terms in their reports or

when testifying without a clear explanation of the term’s significance and

limitations.5

10. Experts should not use the term “scientific” when testifying unless

the basis for their opinions has been scientifically validated.

11. Trial judges should not declare a witness to be an expert in the

presence of the jury.

12. Attorneys have an obligation to understand the discipline —

including its strengths and limitations — underlying the expert testimony that is

presented at trial and to appreciate the importance of consulting with experts prior

to trial.6

13. The proponent of the expert testimony should not cause an expert to

testify beyond the opinion submitted in discovery or beyond the limits of the

laboratory’s testing protocols. 

14. Attorneys should not mischaracterize expert evidence in their

comments to the jury.

3

In this context, “misleading” does not imply an intent to mislead; the effect of

the testimony on the jury is the focus. In short, a jury can be misled even in the absence of an

intent to mislead. See FED. R. EVID. 403 (“misleading the jury”); Daubert v. Merrell Dow Pharm.,

Inc., 509 U.S. 579, 595 (1993) (“Expert evidence can be both powerful and quite misleading

because of the difficulty in evaluating it.”) (quoting Jack B. Weinstein, Rule 702 of the Federal

Rules of Evidence Is Sound: It Should Not Be Amended, 138 F.R.D. 631, 632 (1991)); NATIONAL

RESEARCH COUNCIL, NATIONAL ACADEMY OF SCIENCES, STRENGTHENING FORENSIC SCIENCE IN

THE UNITED STATES: A PATH FORWARD 4 (2009) (“imprecise or exaggerated expert testimony has

sometimes contributed to the admission of erroneous or misleading evidence”). 

4 For example: “zero error rate” and “100 percent accurate.” See NAS FORENSIC

SCIENCE REPORT, supra note 3, at 142-43. These terms are discussed below. 

5 For example: “match” and “consistent with.” Id. at 21. These terms are

discussed below. 

6 The American Bar Association has made competence the first requirement in the

rules of professional conduct. See ABA MODEL RULES OF PROF’L CONDUCT R. 1.1(a)

(“Competent representation requires . . . thoroughness and preparation reasonably necessary for the

representation.”). Moreover, the Supreme Court has decided several recent cases on the 

Sixth Amendment right to effective assistance of counsel. See Hinton v. Alabama, 134 S. Ct. 1081

(2014) (finding counsel ineffective for failing to understand how to retain a defense expert);

Harrington v. Richter, 131 S. Ct. 770, 788 (2011) (“Criminal cases will arise where the only

reasonable and available defense strategy requires consultation with experts or introduction of

expert evidence.”).

2
DIRECTIVE RECOMMENDATIONS

1. The Attorney General should direct federal prosecutors, forensic

laboratories within the Department of Justice, and laboratories under contract with

the Department of Justice to follow the policies outlined above that are applicable

to their duties.

2. The Attorney General should request that the Organization for

Scientific Area Committees (OSAC) consider these policies in their best practices

and standards development.

3. The Attorney General should ask other jurisdictions to consider

adopting the policies outlined above.

BACKGROUND

The National Academy of Sciences (NAS) report7

 on forensic science

raised numerous issues about the presentation of expert testimony at trial, noting

that “imprecise or exaggerated expert testimony has sometimes contributed to the

admission of erroneous or misleading evidence.”8 Such evidence undercuts the

justification for expert testimony. In Kumho Tire Company, Ltd. v. Carmichael,

9

 

the Supreme Court wrote: “Daubert pointed out that Federal Rules 702 and 703

grant expert witnesses testimonial latitude unavailable to other witnesses on the

‘assumption that the expert’s opinion will have a reliable basis in the knowledge

and experience of his discipline.’”10 This memo identifies a number of problems

that have arisen in the presentation of expert testimony in criminal prosecutions.11

7 NATIONAL RESEARCH COUNCIL, NATIONAL ACADEMY OF SCIENCES,

STRENGTHENING FORENSIC SCIENCE IN THE UNITED STATES: A PATH FORWARD (2009) [hereinafter

NAS FORENSIC SCIENCE REPORT].

8

Id. at 4.

9

526 U.S. 137 (1999) (quoting Daubert and pointing out that experts may testify

to opinions, including those that are not based on firsthand knowledge or observation).

10 Id. at 147.

11 The courts, however, have not applied Daubert rigorously in criminal cases:

“The bottom line is simple: In a number of forensic science disciplines, forensic science

professionals have yet to establish either the validity of their approach or the accuracy of their

conclusions, and the courts have been utterly ineffective in addressing this problem.” NAS

FORENSIC SCIENCE REPORT, supra note 3, at 53. See also id. at 106 (“Review of reported judicial

opinions reveals that, at least in criminal cases, forensic science evidence is not routinely

scrutinized pursuant to the standard of reliability enunciated in Daubert. . . . As the reported cases

suggest, however, Daubert has done little to improve the use of forensic science evidence in

criminal cases.”). 

3
I. TESTIFYING BEYOND THE LIMITS OF THE LABORATORY REPORT

State v. Troedel12illustrates this problem. Defendants Troedel and

Hawkins were convicted of capital murder in separate trials. A report of a

gunshot residue test using neutron activation analysis concluded that swabs “from

the hands of Troedel and Hawkins contained antimony and barium in amounts

typically found on the hands of a person who has discharged a firearm or has had

his hands in close proximity to a discharging firearm.”13 The expert testified in

accordance with this report at Hawkins’ trial but enhanced his testimony at

Troedel’s trial, where he testified that “Troedel had fired the murder weapon.”14

Troedel’s conviction was upheld by the state courts. During federal habeas

proceedings, the expert’s deposition was taken, at which time he testified that “he

could not, from the results of his tests, determine or say to a scientific certainty

who had fired the murder weapon” and the “amount of barium and antimony on

the hands of Troedel and Hawkins were basically insignificant.”15

 

The district court found the trial testimony “at the very least” misleading. 

The expert claimed that the prosecutor had “pushed” him further in Troedel’s

trial, a claim that the prosecutor substantiated: “[O]ne of the prosecutors testified

[at the habeas hearing] that, at Troedel’s trial, after [the expert] had rendered his

opinion which was contained in his written report, the prosecutor pushed to ‘see if

more could have been gotten out of this witness.’ When questioned why, in the

Hawkins trial, he did not use [the expert] opinion that Troedel had fired the

weapon, the prosecutor responded he did not know why.”16 In granting habeas

relief, the court observed:

In light of this admission, the above testimony received at the evidentiary

hearing and the inconsistent positions taken by the prosecution at

Hawkins’ and Troedel’s trials, respectively, the Court concludes that the

opinion Troedel had fired the weapon was known by the prosecution not to

be based on the results of the neutron activation analysis tests, or on any

scientific certainty or even probability. Thus, the subject testimony was

not only misleading, but also was used by the State knowing it to be

misleading.17

12 Troedel v. Wainwright, 667 F. Supp. 1456 (S.D. Fla. 1986), aff’d, 828 F.2d 670

(11th Cir. 1987).

13 Id. at 1458.

14 Id. at 1459.

15 Id.

16 Id. at 1459.

17 Id. at 1459-60.

4
(The court also found Troedel’s counsel ineffective. Because defense counsel

knew that the gunshot residue testimony was “critical,” his “failure either to

depose the State’s expert witness or, more importantly, to consult with any other

expert in the field, fell outside the scope of reasonably professional assistance.”18) 

Witness Preparation

As Troedel demonstrates, attorneys bear significant responsibility for the

presentation of expert testimony. The adversary process requires attorneys to put

forth their strongest case, a requirement that incents lawyers to encourage their

witnesses to testify in a way most favorable to their client’s position.19

 Sometimes

the pressure is overt.20 At other times it is subtle but nevertheless unmistakable.21

The issue has arisen so often that the ABA Standards on Criminal Justice includes

this provision: “A prosecutor who engages an expert for an opinion should

respect the independence of the expert and should not seek to dictate the

formation of the expert’s opinion on the subject.”22 The commentary to the

Standard reads: 

Statements made by physicians, psychiatrists, and other experts about their

experiences as witnesses in criminal cases indicate the need for

circumspection on the part of prosecutors who engage experts. Nothing

should be done by the prosecutor to cast suspicion on the process of justice

18 Id. at 1461.

19 See Michael J. Saks, Accuracy v. Advocacy: Expert Testimony Before the Bench,

TECH. REV. 43, 44-45 (1987) (“[E]xperts [are] vulnerable to the possibly distorting influence of

lawyers. Long before the expert and lawyers arrive in court, a bond has formed between them. 

The influence of the lawyer is considerable.”); John I. Thornton, Uses and Abuses of Forensic

Science, 69 ABA J. 288, 292 (1983) (“The evidence will be selected or rejected with only those

items that conform to the arguments of one side actually being submitted for examination. A

distinct possibility exists that the results of the examination by the forensic scientist will be skewed

. . .. These situations represent potential sources of mischief . . .. The danger is that conflicts

easily arise between scientist and lawyer — the former attempts to describe the evidence as it

actually is, while the latter attempts to describe it in the most favorable light.”).

20 See Bank of Nova Scotia v. United States, 487 U.S. 250, 258 (1988) (stating that

the “District Court further concluded that one of the prosecutors improperly argued with an expert

witness during a recess of the grand jury after the witness gave testimony adverse to the

government”); Flynn McRoberts & Steve Mills, From the Start, A Fault Science: Testimony on

Bite Marks Prone to Error, CHI. TRIB., Oct. 19, 2004 (“You get pushed a little bit by prosecutors,

and sometimes you say OK to get them to shut up. . . . ‘I allowed myself to be pushed.’”) (quoting

a forensic dentist).

21 See BARRY SCHECK ET AL., ACTUAL INNOCENCE: FIVE DAYS TO EXECUTION AND

OTHER DISPATCHES FROM THE WRONGLY CONVICTED 31 (2000) (“Asked later if he was pressured

to change his findings on Coakley, [Dr.] Shaler [the expert] said no. ‘Most attorneys,’ Shaler

would also say, ‘like to let you know what their opinions of the facts of the case are — irrespective

of the scientific conclusions.’”).

22 ABA STANDARDS ON CRIMINAL JUSTICE, PROSECUTION AND DEFENSE

FUNCTION, Standard 3-3.3(a) (3d ed. 1993).

5
by suggesting that the expert color an opinion to favor the interests of the

prosecutor.23 

A comparable standard applies to defense counsel — and for the same reasons.24

* * *

In sum, experts should not testify beyond the opinions expressed in their

laboratory reports. If an expert changes her opinion, a supplementary report

should be written and disclosed. This is consistent with the “continuing duty to

disclose” (which is found in pretrial discovery rules) and is intended to prevent

trial by ambush. Such a requirement also provides experts with some protection

from overreaching by litigators. 

II. TESTIFYING BEYOND THE LIMITS OF LABORATORY PROTOCOLS

Inconsistent testimony concerning the same technique probably occurs

because experts do not follow laboratory protocols when testifying and because

their testimony is not monitored by the laboratory.

25

 This was a major problem in

the bullet lead cases. Comparative analysis of bullet lead compared trace

chemicals found in bullets at crime scenes with ammunition found in the

possession of a suspect.26 For over thirty years experts testified about bullet lead

composition, a technique that was first used in the investigation into President

Kennedy’s assassination. 

The published cases reveal a wide variety of interpretive conclusions. In

some cases, experts testified only that two exhibits were “analytically

indistinguishable.”27

 In other cases, experts concluded that samples could have

come from the same “source” or “batch.”28 In still other cases, experts stated that

the samples came from the same source.29 The testimony in a number of cases

went further and referred to a “box” of ammunition (usually fifty loaded

23 Id. cmt. at 59.

24 Id. Standard 4-4.4(a).

25 The lack of a protocol could also cause inconsistent testimony.

26 Various analytical techniques (e.g., neutron activation analysis, inductively

coupled plasma-atomic emission spectrometry) have been used to determine the concentrations of

seven elements — arsenic, antimony, tin, copper, bismuth, silver, and cadmium — in the bullet

lead alloy of both the crime-scene and suspect’s bullets. Statistical tests are then used to compare

the elements in each bullet.

27 Wilkerson v. State, 776 A.2d 685, 689 (Md. Ct. Spec. App. 2001).

28 State v. Krummacher, 523 P.2d 1009, 1012-13 (Or. 1974) (en banc).

29 United States v. Davis, 103 F.3d 660, 673-74 (8th Cir. 1996); People v. Lane,

628 N.E.2d 682, 689-90 (Ill. App. Ct. 1993) (“He testified that the two bullets were analytically

indistinguishable. Special Agent Riley opined that the two bullets came from the same source and

that the match was as good as he had ever seen in his twenty years with the FBI.”).

6
cartridges, sometimes twenty). For example, two specimens:

• Could have come from the same box,30

• Could have come from the same box or a box manufactured on the same

day,

31

• Were consistent with their having come from the same box of

ammunition,32

• Probably came from the same box,33

• Must have come from the same box or from another box that would have

been made by the same company on the same day.

34

Several other (and different) statements appear in the opinions. An early

case reported that the specimens “had come from the same batch of ammunition: 

they had been made by the same manufacturer on the same day and at the same

hour.”35 One case reports the expert’s conclusion with a statistic.36 In another

case, the expert used the expressions “rare finding”37 and “a very rare finding.”38

In still another case, the expert “opined that the same company produced the

bullets at the same time, using the same lead source. Based upon Department of

Justice records, she opined that an overseas company called PMC produced the

bullets around 1982.”39

In later years, the testimony became more limited. A 2002 publication

states the conclusion as follows: “Therefore, they likely originated from the same

30 State v. Strain, 885 P.2d 810, 817 (Utah Ct. App. 1994); State v. Jones, 425

N.E.2d 128, 131 (Ind. 1981).

31 State v. Grube, 883 P.2d 1069, 1078 (Idaho 1994); People v. Johnson, 499

N.E.2d 1355, 1366 (Ill. 1986); State v. Earhart, 823 S.W.2d 607, 614 (Tex. Crim. App. 1991) (en

banc) (“He later modified that statement to acknowledge that analytically indistinguishable bullets

which do not come from the same box most likely would have been manufactured at the same

place on or about the same day; that is, in the same batch.”), vacated, 509 U.S. 517 (1993).

32 State v. Reynolds, 297 S.E.2d 532, 534 (N.C. 1982).

33 Bryan v. Oklahoma, 935 P.2d 338, 360 (Okla. Crim. App. 1997).

34 United States v. Davis, 103 F.3d 660, 666-67 (8th Cir. 1996) (“An expert

testified that such a finding is rare and that the bullets must have come from the same box or from

another box that would have been made by the same company on the same day.”); Commonwealth

v. Daye, 587 N.E.2d 194, 207 (Mass. 1992); State v. King, 546 S.E.2d 575, 584 (N.C. 2001) (The

expert “opined that, based on her lead analysis, the bullets she examined either came from the

same box of cartridges or came from different boxes of the same caliber, manufactured at the same

time.”). 

35 Brown v. State, 601 P.2d 221, 224 (Alaska 1979) (emphasis added).

36 State v. Earhart, 823 S.W.2d 607, 614 (Tex. Crim. App. 1991).

37 United States v. Davis, 103 F.3d 660, 666 (8th Cir. 1996).

38 Id. at 667.

39 People v. Villarta, No. H021354, 2002 Cal. App. Unpub. Lexis 4776, at *15

(Cal. Ct. App. Jan. 17, 2002). 

7
manufacturer’s source (melt) of lead.”40

 Testimony to the same effect was also

proffered: “Well, bullets that are analytically indistinguishable likely come from

the same molten lead sources of lead, uh, as opposed to bullets that have different

composition come from different, uh, melts of lead.”41

A 2004 NAS report undercut this testimony, finding that the amount of

bullets that can be produced from a melt “can range from the equivalent of as few

as 12,000 to as many as 35 million 40grain, .22 caliber longrifle bullets.”42 Based

on this finding, the report concluded: “The available data do not support any

statement that a crime bullet came from a particular box of ammunition. In

particular, references to ‘boxes’ of ammunition in any form should be avoided as

misleading under Federal Rule of Evidence 403.”43 

III. WITHHOLDING INFORMATION AT TRIAL

In Driscoll v. Delo,

44

 a capital murder case, the laboratory report indicated

that blood traces on Driscoll’s knife were type A, which matched the blood of a

prison guard who had been injured by a stab wound but did not match the blood

type of a murdered guard whose blood type was O. To explain the absence of

type O blood, the prosecution offered several theories, one of which was that the

presence of the type O blood was “masked” by the type A blood. The chief

serologist of the state crime laboratory testified about this theory at trial. Only in

a subsequent habeas proceeding was it revealed that the serologist had performed

another test, which had eliminated the “masking” problem, revealing the lack of

type O blood. “The jury was never informed that the lattes test was performed or

that no type O blood was on the knife . . .. In its closing argument, the state made

much of the masking theory, turning unfavorable serology evidence into neutral

evidence at worst.”45

40 Charles A. Peters, The Basis for Compositional Bullet Lead Comparisons, 4

FORENSIC SCI. COMMUNICATIONS No. 3, at 5 (July 2002) (emphasis added).

41 Transcript of Trial Testimony of Charles Peters, Commonwealth v. Wilcox,

Kentucky, Feb. 28, 2002. 

42 Id.

43 NATIONAL RESEARCH COUNCIL, NATIONAL ACADEMY OF SCIENCES, FORENSIC

ANALYSIS: WEIGHING BULLET LEAD EVIDENCE 6 (2004).

44 71 F.3d 701, 707 (8th Cir. 1995). The effective assistance of counsel was also

raised: Whether alleged murder weapon “had blood matching the victim’s constituted an issue of

the utmost importance. Under these circumstances, a reasonable defense lawyer would take some

measures to understand the laboratory tests performed and the inferences that one could logically

draw from the results. At the very least, any reasonable attorney under the circumstances would

study the state’s laboratory report with sufficient care so that if the prosecution advanced a theory

at trial that was at odds with the serology evidence, the defense would be in a position to expose it

on cross-examination.” Id. at 709. 

45 Id. at 708.

8
In the Cruz and Hernandez prosecutions, the misuse of scientific evidence

as well as other evidence led a police officer and an Assistant Attorney General to

resign in protest during the initial proceedings and eventually lead to trials of the

original prosecutors and police officers.46 For example: 

When a crime technician arrived at the courthouse to testify for the state,

he pulled aside one of the prosecutors and relayed some news: 

representatives from the Nike shoe company said that the prints at the back

window had been made by a woman’s shoe, perhaps size six or five and a

half. Either size was too small for Cruz or Hernandez. The prosecutor put

the technician on the witness stand and carefully avoided any mention of

the shoe size or likely gender. In fact, the defense was not told about the

Nike analysis.47

The defendants were later exonerated by DNA analysis.48

In Mitchell v. Gibson,

49

 an expert provided the jury with evidence

implicating the accused in an sexual assault, which — based on evidence withheld

from the defense — the expert knew was misleading. The Tenth Circuit observed

that this improper conduct was compounded by “the prosecutor, whom the district

court found had ‘labored extensively at trial to obscure the true DNA test results

and to highlight [the expert’s] test results,’ and whose characterization of the FBI

report in his closing argument was ‘entirely unsupported by evidence and . . .

misleading.’”50

46 See Barry Siegel, Presumed Guilty; An Illinois Murder Case Becomes a Test of

Conscience Inside the System, L.A. TIMES, Nov. 1, 1992, (Magazine) at 18 (quoting former

detective John Sam); Brandon L. Garrett, CONVICTING THE INNOCENT: WHERE CRIMINAL

PROSECUTIONS GO WRONG (2011) (discussing case)..

47 SCHECK ET AL., supra note 21, at 178.

48 EDWARD CONNORS ET AL., NAT’L INST. OF JUSTICE, CONVICTED BY JURIES,

EXONERATED BY SCIENCE: CASE STUDIES IN THE USE OF DNA EVIDENCE TO ESTABLISH

INNOCENCE AFTER TRIAL 44 (1996) (discussing cases of Rolando Cruz and Alejandro Hernandez)

[hereinafter Exonerated by Science]. See also Brandon L. Garrett & Peter J. Neufeld, Invalid

Forensic Science Testimony and Wrongful Convictions, 95 VA. L. REV. 1 (2009) (The study

identified several different types of invalid testimony: (1) presenting non-probative evidence as

probative, (2) discounting exculpatory evidence, (3) using inaccurate frequencies or statistics, (4)

providing a statistic without support, (5) providing non-numerical statements without empirical

support, and (6) attributing the source of evidence to the defendant.). 

49 262 F.3d 1036 (10th Cir. 2001). “The results thus completely undermined Ms.

Gilchrist’s testimony.” Id. at 1064 (emphasis in original) (“An expert testified at the evidentiary

hearing that the DNA testing performed by Agent Vick unquestionably eliminated Mr. Mitchell . . .

. This expert reviewed Ms. Gilchrist’s trial testimony . . . and stated that the testimony was based

on the use of test methods Ms. Gilchrist knew were less precise than the DNA tests which

eliminated Mr. Mitchell. Moreover, he pointed out that one of the tests she performed in fact

excluded Mr. Mitchell.”).

50 Id.

9
In the North Carolina Innocence Inquiry Commission’s investigation into

the Greg Taylor case, the bench notes of the serologist, who had examined

evidence for Taylor’s original trial, surfaced. The lab report noted that there were

“chemical indications for the presence of blood.”51 In contrast, the bench notes

showed that a subsequent confirmatory test was negative. These results were not

disclosed to the prosecution or the defense at trial. As a result of this disclosure,

the State Attorney General commissioned an investigation into the lab’s practices,

which was conducted by two former FBI officials. They concluded:

This report raises serious issues about laboratory reporting

practices from 1987-2003 and the potential that information that was

material and even favorable to the defense of criminal charges filed was

withheld or misrepresented. The factors that contributed to these issues

range from poorly crafted policy; lack of objectivity[;] the absence of clear

report writing guidance; inattention to reporting methods that left too

much discretion to the individual Analyst[;] lack of transparency; and

ineffective management and oversight of the Forensic Biology Section

from 1987 through 2003.52 

In particular, the investigation identified four different types of improper

reporting. These included reports that: (1) mentioned that tests for the presence

of blood are not conclusive but fail to report a confirmatory negative test; (2)

failed to mention one or more negative or inconclusive confirmatory tests; (3)

stated that no further tests were conducted when, in fact, one or more

confirmatory tests were conducted with negative or inconclusive results; and (4)

overstated laboratory test results or where lab notes contradicted reported result.53

IV. OVERSTATEMENTS IN TESTIMONY

Cases in which expert testimony goes beyond the limitations of a scientific

technique are not uncommon.54 For example, hair evidence has frequently been

51 Mike Klinkosum, State v. Taylor and the North Carolina State Bureau of

Investigation Lab Scandal, CHAMPION 10 (May 2011). 

52 CHRIS SWECKER & MICHAEL WOLF, AN INDEPENDENT REVIEW OF THE SBI

FORENSIC LABORATORY 4 (2010), available at http://www.ncids.com/forensic/sbi/Swecker_

Report.pdf.

53 Id. at 3.

54 See State v. Spencer, 216 N.W.2d 131, 134 (Minn. 1974) (“We are concerned . .

. about the sweeping and unqualified manner in which [the expert’s] testimony was offered . . . . 

An expert witness could be permitted to testify that in his opinion the chemicals present on

defendant’s hand may have resulted from the firing of a gun. He should not have been permitted to

state, as he did, that this defendant had definitely fired a gun.”); Dennis S. Karjala, The Evidentiary

Uses of Neutron Activation Analysis, 59 CAL. L. REV. 997, 1024 (1971) (“[F]ew experts have used

appropriate care in limiting their testimony.”).

10
misused.55

 In one case, the expert testified that the crime scene hair sample “was

unlikely to match anyone” other than the defendant, Edward Honaker.56 At best,

the expert could have testified that the hairs were “consistent,” which means that

they could have come from Honaker or thousands of other people.57 Honaker was

later exonerated by DNA testing. 

Similarly, in Williamson v. Reynolds,

58

 the expert testified that hair

samples were “consistent microscopically”

59

 and then went on to explain what this

meant: “In other words, hairs are not an absolute identification, but they either

came from this individual or there is — could be another individual somewhere in

the world that would have the same characteristics to their hair.”60

 Five days

before Williamson’s scheduled execution for murder, a federal judge granted his

petition for habeas relief. He was later exonerated by DNA testing.61

V. TESTIFYING BEYOND EXPERTISE; LAY TESTIMONY

An expert’s testimony must relate to the subject matter on which the

expert has been qualified. “It goes without saying that an expert qualified to testify

upon one topic may be completely unqualified to testify about another as to which

he lacks special knowledge, skill, experience, or training, but some applications of

this principle take the unwary by surprise.”62 In People v. Ayala,

63

 an expert

recognized this limitation: “Dr. Kellerhouse acknowledged that he was not a

ballistics expert, and declined to testify about the bullets’ caliber .... As a

radiologist, Dr. Kellerhouse could testify that the bullets were located so that their

relative size would not be distorted in the X-ray photographs.”64

55

“Sixty-five of the trials examined involved microscopic hair comparison

analysis. Of those, 25 — or 38% — had invalid hair comparison testimony. Most (18) of these

cases involved invalid individualizing claims.” Brandon L. Garrett & Peter J. Neufeld, Invalid

Forensic Science Testimony and Wrongful Convictions, 95 VA. L. REV. 1, 47 (2009). 

56 EXONERATED BY SCIENCE, supra note 48, at 65 (emphasis added). 

57 See B.D. Gaudette, Probabilities and Human Pubic Hair Comparisons, 21 J.

FORENSIC SCI. 514, 514 (1976) (“If a pubic hair from the scene of a crime is found to be similar to

those from a known source, [the courts] do not know whether the chances that it could have

originated from another source are one in two or one in a billion.”). 

58 904 F. Supp. 1529, 1558 (E.D. Okl. 1995), aff’d, 110 F.3d 1508, 1523 (10th Cir.

1997).

59 Id. at 1554.

60 Id. (emphasis added). 

61 See JOHN GRISHAM, THE INNOCENT MAN: MURDER AND INJUSTICE IN A SMALL

TOWN (2006) (discussing Williamson case).

62 JOHN MAGUIRE, EVIDENCE: COMMON SENSE AND COMMON LAW 30-31 (1947).

63 6 P.3d 193 (Cal. 2000).

64 Id. at 215.

11
Further, a witness may be an expert on one aspect of a technique but not

on other aspects. Accordingly, courts must “differentiate between ability to

operate an instrument or perform a test and the ability to make an interpretation

drawn from use of the instrument.”65 For example, a police officer may be

qualified to conduct a horizontal gaze nystagmus test (an intoxication test) but not

be qualified to interpret the results. 

[The officer’s] opinion that appellant was under the influence of alcohol,

to the extent it was based on the nystagmus test, rests on scientific

principles well beyond his knowledge, training, or education. Without

some understanding of the processes by which alcohol ingestion produces

[eye] nystagmus, how strong the correlation is, how other possible causes

might be masked, what margin of error has been shown in statistical

surveys, and a host of other relevant factors, [the officer’s] opinion on

causation, notwithstanding his ability to recognize the symptom, was

unfounded.66

Moreover, a witness may testify as both a lay (fact) witness and an expert

witness — e.g., a pathologist performing an autopsy.

67

 The Federal Rules do “not

distinguish between expert and lay witnesses, but rather between expert and lay

testimony. Certainly it is possible for the same witness to provide both lay and

expert testimony in a single case.”68

 Attorneys and experts should appreciate the

difference.

VI. MISLEADING TERMS IN TESTIMONY

As noted above, the NAS report on forensic science raised numerous

issues about the presentation of expert testimony at trial, noting that “imprecise or

exaggerated expert testimony has sometimes contributed to the admission of

erroneous or misleading evidence.”69 The report later voiced concern about the

use of terms such as “match,” “consistent with,” “identical,” “similar in all

respects tested,” and “cannot be excluded as the source of.” These terms can have

“a profound effect on how the trier of fact in a criminal or civil matter perceives

and evaluates scientific evidence.”70

65 People v. King, 72 Cal. Rptr. 478, 491 (Cal. Ct. App. 1968).

66 People v. Williams, 5 Cal. Rptr. 2d 130, 135 (Cal. Ct. App. 1992). 

67 Testimony that involves the observation of wounds on a decedent is lay

testimony, while the interpretation of those wounds involves expertise.

68 Fed. R. 701 advisory committee’s note (2000).

69 NAS FORENSIC SCIENCE REPORT, supra note 3, at 4.

70 Id. at 21.

12
The Supreme Court identified the same concern in Daubert: “Expert

evidence can be both powerful and quite misleading because of the difficulty in

evaluating it.”71 Moreover, Federal Rule of Evidence 403 provides: “The court

may exclude relevant evidence if its probative value is substantially outweighed

by a danger of one or more of the following: unfair prejudice, confusing the

issues, misleading the jury, undue delay, wasting time, or needlessly presenting

cumulative evidence.”72

 In this context, “misleading” does not imply an intent to

mislead; the effect of the testimony on the jury is the focus of Rule 403. In short,

a jury can be misled even in the absence of an intent to mislead. Courts are

concerned about the “CSI effect” — i.e., “scientific proof may in some instances

assume a posture of mystic infallibility in the eyes of a jury of laymen.”73

 Courts

often exclude polygraph evidence on this basis.74 

Certain terms should not used in presenting expert testimony because they

are either invalid or confusing. Other terms should not used at trial without an

explanation because of their potential to mislead the trier of fact.

A. “Zero Error Rate”

In United States v. Havvard,

75

 which involved a Daubert challenge to

fingerprint evidence, the expert claimed that the “error rate for the method is

zero.”76

 Note the word method in the above quote. Examiners argued that, while

individual examiners may make mistakes, the methodology itself is perfect. 

However, the dichotomy between “methodological” and “human” error rates in

this context is “practically meaningless”77because the examiner is the method.78

71 Daubert v. Merrell Dow Pharm., Inc., 509 U.S. 579, 595 (1993) (quoting Jack B.

Weinstein, Rule 702 of the Federal Rules of Evidence Is Sound: It Should Not Be Amended, 138

F.R.D. 631, 632 (1991)).

72 FED. R. EVID. 403 (emphasis added).

73 United States v. Addison, 498 F.2d 741, 744 (D.C. Cir. 1974).

74 See United States v. Call, 129 F.3d 1402, 1406 (10th Cir. 1997) (“There is also

the danger that the jury may overvalue polygraph results as an indicator of truthfulness because of

the polygraph’s scientific nature.”); United States v. Falsia, 724 F.2d 1339, 1342 (9th Cir. 1983)

(noting polygraph’s “misleading appearance of accuracy”).

75 117 F. Supp. 2d 848 (S.D. Ind. 2000), aff’d, 260 F.3d 597 (7th Cir. 2001).

76 Id. at 854.

77 Jennifer L. Mnookin, Fingerprint Evidence in an Age of DNA Profiling, 67

BROOK. L. REV. 13, 60 (2001). Professor Mnookin goes on to provide this analogy: “The same

argument could be made of eyewitness testimony, a notoriously unreliable form of evidence. 

People are all distinct from one another in observable ways; therefore the theoretical error rate of

eyewitness identification is zero, though in practice observers may frequently makes errors.” Id.

See also Simon A. Cole, More Than Zero: Accounting for Error in Latent Fingerprint

Identification, 95 J. CRIM. L. & CRIMINOLOGY 985, 1040 (2005) (“in fingerprint practice the

concept is vacuous”). Professor Cole identified twenty-two misidentifications, which he argues

“are most likely only the tip of the proverbial iceberg of actual cases of fingerprint misattribution.” 

Id. at 991. The misidentification cases include some that involved (1) verification by one or more

13
The 2009 NAS report addressed this point: “Although there is limited

information about the accuracy and reliability of friction ridge analyses, claims

that these analyses have zero error rates are not scientifically plausible.”79 The

report goes on to observed: “Some in the latent print community argue that the

method itself, if followed correctly. . . has a zero error rate. Clearly, this assertion

is unrealistic . . .. The method, and the performance of those who use it, are

inextricably linked, and both involve multiple sources of error (e.g., errors in

executing the process steps, as well as errors in human judgment.)”80

Several courts also commented on this issue. For example, in United

States v. Mitchell,

81

 the Third Circuit wrote: “Testimony at the Daubert hearing

indicated that some latent fingerprint examiners insist that there is no error rate

associated with their activities . . . . This would be out-of-place under Rule

702.”82 The same issue arose in a firearms identification case. In United States v.

Glynn,

83

 the court wrote that “[t]he problem is compounded by the tendency of

ballistics experts . . . to make assertions that their matches are certain beyond all

doubt, that the error rate of their methodology is ‘zero,’ and other such

pretensions.”84

B. “Hundred Percent Accurate”

In a different firearms identification case, United States v. Monteiro,

85

the

court noted:

[T]he examiners testified to the effect that they could be 100 percent sure

of a match. Because an examiner’s bottom line opinion as to an

identification is largely a subjective one, there is no reliable statistical or

scientific methodology which will currently permit the expert to testify

that it is a “match” to an absolute certainty, or to an arbitrary degree of

other examiners, (2) examiners certified by the International Association of Identification, (3)

procedures using a sixteen-point standard, and (4) defense experts who corroborated

misidentifications made by prosecution experts.

78 See Sandy L. Zabell, Fingerprint Evidence, 13 J.L. & POL’Y 143, 172 (2005)

(“But, given its unavoidable subjective component, in latent print examination people are the

process.”) (emphasis added).

79 NAS FORENSIC SCIENCE REPORT, supra note 3, at 142.

80 Id. at 143.

81 365 F.3d 215 (3d Cir. 2004) (admitting fingerprint evidence).

82 Id. at 245-46. Rule 702 is the governing rule on expert testimony.

83 578 F. Supp. 2d 567 (S.D.N.Y. 2008).

84 Id. at 574.

85 407 F. Supp. 2d 351 (D. Mass. 2006).

14
statistical certainty.

86

The 2009 NAS report concurred: “The insistence by some forensic practitioners

that their disciplines employ methodologies that have perfect accuracy and

produce no errors has hampered efforts to evaluate the usefulness of the forensic

science disciplines.”87

In its first report on DNA profiling, the National Academy of Sciences

report commented: “Prosecutors and defense counsel should not oversell DNA

evidence. Presentations that suggest to a judge or jury that DNA typing is

infallible are rarely justified and should be avoided.”88

C. “Scientific” 

The use of terms such as “science” or “scientific” in presenting expert

testimony is also problematic.89 In 1995, a federal district court in United States v.

Starzecpyzel90 concluded that “forensic document examination, despite the

existence of a certification program, professional journals and other trappings of

science, cannot, after Daubert, be regarded as ‘scientific . . . knowledge.’”91 The

court further stated that “while scientific principles may relate to aspects of

handwriting analysis, they have little or nothing to do with the day-to-day tasks

performed by [Forensic Document Examiners] . . . . [T]his attenuated relationship

does not transform the FDE into a scientist.”92 

Although the court went on to admit the testimony as technical evidence, it 

placed conditions on its admissibility.

93

 Because FDEs use terms such as

“laboratory” and refer to authorities with titles containing the words “science” or

“scientific,” there is a risk, according to the court, that jurors may bestow upon

86 Id. at 372 (emphasis added).

87 NAS FORENSIC SCIENCE REPORT, supra note 3, at 47.

88 NATIONAL RESEARCH COUNCIL, NATIONAL ACADEMY OF SCIENCES, DNA

TECHNOLOGY IN FORENSIC SCIENCE 26 (1992).

89 Philosophers of science disagree about the definition of “science.” The Supreme

Court quoted one definition in Daubert: KARL POPPER, CONJECTURES AND REFUTATIONS: THE

GROWTH OF SCIENTIFIC KNOWLEDGE 37 (5th ed. 1989) (“[T]he criterion of the scientific status of a

theory is its falsifiability, or refutability, or testability.”). Daubert, 509 U.S. at 593.

90 880 F. Supp. 1027 (S.D.N.Y. 1995).

91 Id. at 1038.

92 Id. at 1041.

93 In the court’s view, Daubert did not apply to nonscientific experts. The court

relied on the following statement in Daubert: “Our discussion is limited to the scientific context

because that is the nature of the expertise offered here.” 509 U.S. at 590 n.8. This position was

undercut by Kumho Tire, which held that all expert testimony must pass the Daubert reliability

test. Kumho Tire Co., Ltd. v. Carmichael, 526 U.S. 137, 149 (1999).

15
FDEs the aura of the infallibility of science. The court approved a jury

instruction, which stated that “FDEs offer practical, rather than scientific

expertise.”94 Similarly, in United States v. Glynn,

95

 a firearms identification case,

the court observed: “Based on the Daubert hearings . . . , the Court very quickly

concluded that whatever else ballistics identification analysis could be called, it

could not fairly be called ‘science.’”96

The NAS report provides support for this position: “The law’s greatest

dilemma in its heavy reliance on forensic evidence . . . concerns the question of

whether — and to what extent — there is science in any given forensic science

discipline.”97

 A subsequent passage concluded: “Among existing forensic

methods, only nuclear DNA analysis has been rigorously shown to have the

capacity to consistently, and with a high degree of certainty, demonstrate a

connection between an evidentiary sample and a specific individual or source.”98

Other passages are in accord.99

Many forensic identification disciplines are ultimately subjective, and

there are often no meaningful standards100 — factors that undercut claims that

these techniques are “scientific.”101

94 880 F. Supp. at 1049.

95 578 F. Supp. 2d 567 (S.D.N.Y. 2008).

96 Id. at 570.

97 NAS FORENSICS SCIENCES REPORT, supra note 3, at 9.

98 Id. at 100.

99

“The simple reality is that the interpretation of forensic evidence is not always

based on scientific studies to determine its validity. This is a serious problem. Although research

has been done in some disciplines, there is a notable dearth of peer-reviewed, published studies

establishing the scientific bases and validity of many forensic methods.” Id. at 8. “Much forensic

evidence — including, for example, bite marks and firearm and toolmark identifications — is

introduced in criminal trials without any meaningful scientific validation, determination of error

rates, or reliability testing to explain the limits of the discipline.” Id. at 107-08

100

“Often there are no standard protocols governing forensic practice in a given

discipline. And, even when protocols are in place . . . , they often are vague and not enforced in

any meaningful way.” Id. at 6. 

101 Jennifer L. Mnookin, et al., The Need for a Research Culture in the Forensic

Sciences, 58 UCLA L. Rev. 725, 731 (2011) (“In our collective opinion, the pattern identification

disciplines, as well as other forms of forensic science evidence, must be placed on a more rigorous

scientific foundation. More generally, we believe that a significant culture shift is required: 

Forensic science needs to focus more on science than on law, to shift from a quasi-adversarial

perspective to a research orientation. In short, we call for the development and instantiation of

what we will term a research culture within forensic science”); Jennifer L. Mnookin, The Courts,

The NAS, and the Future of Forensic Science, 75 BROOKLYN L. REV. 1209, 1215 (2010) (“This

forensic science culture — a culture in which claims derived from experience are often accepted as

a substitute for data; a culture in which interpretations are often framed in absolute terms rather

than in more limited or modest language; a culture in which potentially biasing information is not

systematically kept from the forensic examiner; and a culture in which institutionally cozy

relationships between detectives, forensic analysts, and prosecutors may encourage unconscious

16
In Kumho Tire, the Supreme Court rejected the distinction between

“scientific” and “technical” evidence for purposes of applying the Daubert test,

observing that the distinction would be difficult to draw.102 Thus, the

classification of evidence as scientific or nonscientific is not important for

admissibility purposes; all expert testimony must satisfy the Daubert

validity/reliability requirement. However, the term “scientific” may unduly

impress the jury.

103

There is little question that physical evidence (e.g., distinctive shoe print)

can be probative and powerful even though it is not scientific.

D. “Reasonable Degree of Scientific Certainty”

The expression “reasonable scientific certainty,” which is often included

(and sometimes demanded) in expert testimony, is another phrase that should be

abandoned.104 

1. Lack of a Scientific Bases

The phrase, which combines two suspect words — “scientific”105 and

partisanship — remains very much the norm within forensic science laboratories today. It is, in the

end, this culture that needs to change; new and improved forensic techniques will not, by

themselves, provide an adequate solution.”).

102 The Court wrote:

[I]t would prove difficult, if not impossible, for judges to administer evidentiary rules

under which a gatekeeping obligation depended upon a distinction between “scientific”

knowledge and “technical” or “other specialized” knowledge. There is no clear line that

divides the one from the others. Disciplines such as engineering rest upon scientific

knowledge. Pure scientific theory itself may depend for its development upon

observation and properly engineered machinery. And conceptual efforts to distinguish the

two are unlikely to produce clear legal lines capable of application in particular cases. Cf.

Brief for National Academy of Engineering as Amicus Curiae 9 (scientist seeks to

understand nature while the engineer seeks nature’s modification); Brief for Rubber

Manufacturers Association as Amicus Curiae 14-16 (engineering, as an “ ‘applied

science,’ ” relies on “scientific reasoning and methodology”); Brief for John Allen et al.

as Amici Curiae 6 (engineering relies upon “scientific knowledge and methods”).

Kumho Tire, 526 U.S. at 148.

103 See United States v. Addison, 498 F.2d 741, 744 (D.C. Cir. 1974) (“[S]cientific

proof may in some instances assume a posture of mystic infallibility in the eyes of a jury of

laymen.”).

104 The term “reasonable medical certainty” is similarly problematic.

105 See United States v. Glynn, 578 F. Supp. 2d 567, 570 (S.D.N.Y. 2008) (“Based

on the Daubert hearings . . . , the Court very quickly concluded that whatever else ballistics

identification analysis could be called, it could not fairly be called ‘science.’”); United States v.

Starzecpyzel, 880 F. Supp. 1027. 1038, 1041 (S.D.N.Y. 1995) (“forensic document examination,

despite the existence of a certification program, professional journals and other trappings of

17
“certainty” — has no scientific meaning. One scholar summed it up this way:

The reasonable-degree-of-scientific-certainty language almost certainly

was drafted by the lawyers. Scientists have no use for this phrase (outside

the courtroom). Indeed, “a reasonable degree of scientific certainty” is not

a defined concept in scientific disciplines or even in law. . . . It is legal

mumbo jumbo derived from archaic cases in which lawyers discovered

that if a medical doctor did not utter the incantation “to a reasonable

degree of medical certainty,” his testimony might be excluded because

doctors were not supposed to talk about mere probabilities. Modern cases

usually recognize that suitably explained information about less-thancertain possibilities can be helpful in various circumstances, but experts

want to (or are induced to) incant not only “medical certainty” but also

“clinical certainty,” “psychological certainty,” “psychiatric certainty,”

“engineering certainty,” “architectural certainty,” “ballistic certainty,”

“professional certainty,” and even “forensic certainty” and “legal

certainty.”106

The requirement that experts testify in terms of probability most likely originated

as a “sufficiency” rule in civil cases in which causation was an issue. The

plaintiff in a civil action would have to prove causation by preponderance of

evidence (i.e., more probable than not). The term may then have been improperly

transmuted into an “admissibility” rule in civil cases and then improperly applied

in criminal cases.107 

2. Federal Rules of Evidence

Article VII of the Federal Rules of Evidence, which governs expert

testimony, does not require the use of the phrase “reasonable scientific (or

medical) certainty, as some courts have recognized: “There is no such

requirement.”108 It is a common law requirement that, at least in theory, was

science, cannot, after Daubert, be regarded as ‘scientific . . . knowledge.’”; “while scientific

principles may relate to aspects of handwriting analysis, they have little or nothing to do with the

day-to-day tasks performed by [Forensic Document Examiners] . . . . [T]his attenuated

relationship does not transform the FDE into a scientist.”). See also NAS FORENSICS SCIENCES

REPORT, supra note 3, at 9, 107-08 (“The law's greatest dilemma in its heavy reliance on forensic

evidence . . . concerns the question of whether — and to what extent — there is science in any

given forensic science discipline.”; “Much forensic evidence — including, for example, bite marks

and firearm and toolmark identifications — is introduced in criminal trials without any meaningful

scientific validation, determination of error rates, or reliability testing to explain the limits of the

discipline.”).

106 DAVID H. KAYE, THE DOUBLE HELIX AND THE LAW OF EVIDENCE 82 (2010).

107 See PAUL C. GIANNELLI, BALDWIN’S OHIO PRACTICE, EVIDENCE § 702.6 (3d ed.

2010) (describing the Ohio experience with the term).

108 United States v. Cyphers, 553 F.2d 1064, 1072 (7th Cir. 1977).

18
abolished by Federal Rule 402, which makes all relevant evidence in the absence

of a rule of exclusion.109

3. Ambiguous and Misleading

Although the phrase is used frequently in cases, its legal meaning is

ambiguous at best.110

 One commentator observed: “Although judges expect, and

sometimes insist, that expert opinions be expressed with ‘reasonable medical

certainty,’ and although attorneys ritualistically intone the phrase, no one knows

what it means! No consensus exists among judges, attorneys, or academic

commentators as to whether ‘reasonable medical certainty’ means ‘more probable

than not’ or ‘beyond a reasonable doubt’ or something in between.”111

The ambiguity of the term is illustrated in Burke v. Town of Walpole,

112

 a

bite mark identification case. The First Circuit had to interpret the term as used in

an arrest warrant: 

[W]e must assume that the magistrate who issued the arrest warrant

assigned no more than the commonly accepted meaning among lawyers

and judges to the term “reasonable degree of scientific certainty” — “a

standard requiring a showing that the injury was more likely than not

caused by a particular stimulus, based on the general consensus of

recognized [scientific] thought.” Black’s Law Dictionary 1294 (8th

ed.2004) (defining “reasonable medical probability,” or “reasonable

medical certainty,” as used in tort actions). That standard, of course, is

fully consistent with the probable cause standard.113

Note that the case involved a magistrate, not a jury. It seems doubtful that a jury

109 Edward J. Imwinkelried & Robert G. Scofield, The Recognition of an Accused's

Constitutional Right to Introduce Expert Testimony Attacking the Weight of Prosecution Science

Evidence: The Antidote for the Supreme Court's Mistaken Assumption in California v. Trombetta,

33 Ariz. L. Rev. 59, 69 (1991) (“Many courts continue to exclude opinions which fall short of

expressing a probability or certainty. . . . These opinions have been excluded in jurisdictions

which have adopted the Federal Rules of Evidence.”).

110 Sometimes the phrase seems to be used as a confidence statement (i.e., “I am

confident of my opinion.”), in which case the expert could avoid the phrase altogether and directly

testify how confident she is in her opinion. See James E. Hullverson, Reasonable Degree of

Medical Certainty: A Tort et a Travers, 31 ST. LOUIS U.L.J. 577, 582 (1987) (“[T]here is

nevertheless an undercurrent that the expert in federal court express some basis for both the

confidence with which his conclusion is formed, and the probability that his conclusion is

accurate.”).

111 Jeff L. Lewin, The Genesis and Evolution of Legal Uncertainty About

“Reasonable Medical Certainty,” 57 MD. L. REV. 380 (1998).

112 405 F.3d 66 (1st Cir. 2005).

113 Id. at 91 (emphasis added). 

19
would understand that the term “reasonable scientific certainty” meant only “more

probable than not” — i.e., 51 percent. It is more likely that the jury would

understand the term to mean 95% certain or perhaps “beyond a reasonable doubt.”

The problem could be rectified by using the phrase “more probable than

not” rather than “reasonable scientific certainty.” However, this solution

introduces it own problems. Federal Rule 401 requires only that evidence be

relevant, not probable. For example, evidence that a suspect had a .38 caliber

handgun and that a .38 caliber bullet was found during a murder victim’s autopsy

satisfies Rule 401.114 But the expert could not say that suspect’s handgun

probably fired the bullet.115

4. Recent Cases

The phrase has come under attack in recent cases. In United States v.

Glynn,

116

the court ruled that the term “reasonable scientific certainty” could not

be used in a firearms identification case. In light of the expert’s admission

concerning the subjective nature of the examination, “the Government did not

seriously contest the Court’s conclusions that ballistics lacked the rigor of science

and that, whatever else it might be, its methodology was too subjective to permit

opinions to be stated to ‘a reasonable degree of ballistic certainty.’”117

Similarly, in United States v. Taylor,

118

 the court wrote: “[B]ecause of the

limitations on the reliability of firearms identification evidence discussed above,

[the expert] will not be permitted to testify that his methodology allows him to

reach this conclusion as a matter of scientific certainty. [The expert] also will not

be allowed to testify that he can conclude that there is a match to the exclusion,

either practical or absolute, of all other guns. He may only testify that, in his

opinion, the bullet came from the suspect rifle to within a reasonable degree of

114 Fed. R. Evid. 401 (“Evidence is relevant if: (a) it has any tendency to make a fact

more or less probable than it would be without the evidence; and (b) the fact is of consequence in

determining the action.”).

115 This type of evidence has been admitted in numerous cases. See, e.g., People v.

Horning, 102 P.3d 228, 236 (Cal. 2004) (expert “opined that both bullets and the casing could

have been fired from the same gun . . . because of their condition he could not say for sure”);

Luttrell v. Commonwealth, 952 S.W.2d 216, 218 (Ky. 1997) (expert “testified only that the bullets

which killed the victim could have been fired from Luttrell’s gun”). 

116 578 F. Supp. 2d 567 (S.D.N.Y. 2008).

117 Id. at 571. In United States v. Willock, 696 F. Supp. 2d 536, 549 (D. Md. 2010),

based on a comprehensive magistrate’s report, the court held that “[the expert] shall not opine that

it is a ‘practical impossibility’ for a firearm to have fired the cartridges other than the common

‘unknown firearm’ to which [the expert] attributes the cartridges.” Thus, “[The expert] shall state

his opinions and conclusions without any characterization as to the degree of certainty with which

he holds them.” Id.

118 663 F. Supp. 2d 1170 (D. N.M. 2009)

20
certainty in the firearms examination field.”119

However, replacing the term “reasonable scientific certainty” with the term

“reasonable ballistic certainty” does not solve the problem.120 That phrase suffers

from the same defects. In sum, the phrase should be abandoned. Jurisdictions

that require the phrase “reasonable scientific (or medical) certainty” should

reconsider its use.

E. Claims of “uniqueness”

Courts have responded in different ways to claims of uniqueness. Due to a

lack of foundational research,121 several courts have limited the scope of

handwriting testimony, permitting expert testimony about the similarities and

dissimilarities between exemplars but not the specific conclusion that the

defendant was the author (“common authorship” opinion).122 Although the courts

have used this approach most frequently in questioned document cases, they have

sometimes applied it to other types of forensic expertise such as firearms

identification examinations.123 One court took a less restrictive approach, ruling

119 Id. at 1180.

120 See also United States v. Diaz, No. CR 05-00167 WHA, 2007 WL 485967, at *1

(N.D. Cal. Feb. 12, 2007) (“[T]he examiners who testify in this case may only testify that a match

has been made to a ‘reasonable degree of certainty in the ballistics field.’”); United States v.

Monteiro, 407 F. Supp. 2d 351, 372 (D. Mass. 2006); Commonwealth v. Pytou Heang, 942 N.E.2d

927, 945 (Mass. 2011) (“Where a qualified expert has identified sufficient individual characteristic

toolmarks reasonably to offer an opinion that a particular firearm fired a projectile or cartridge

casing recovered as evidence, the expert may offer that opinion to a ‘reasonable degree of ballistic

certainty.’”). 

121 See United States v. Hidalgo, 229 F. Supp. 2d 961, 967 (D. Ariz. 2002)

(“Because the principle of uniqueness is without empirical support, we conclude that a document

examiner will not be permitted to testify that the maker of a known document is the maker of the

questioned document. Nor will a document examiner be able to testify as to identity in terms of

probabilities.”); United States v. Fujii, 152 F. Supp. 2d 939, 940 (N.D. Ill. 2000) (“Handwriting

analysis does not stand up well under the Daubert standards. Despite its long history of use and

acceptance, validation studies supporting its reliability are few, and the few that exist have been

criticized for methodological flaws.”).

122 See United States v. Oskowitz, 294 F. Supp. 2d 379, 384 (E.D.N.Y. 2003)

(“Many other district courts have similarly permitted a handwriting expert to analyze a writing

sample for the jury without permitting the expert to offer an opinion on the ultimate question of

authorship.”); United States v. Rutherford, 104 F. Supp. 2d 1190, 1194 (D. Neb. 2000) (“[T]he

Court concludes that FDE Rauscher’s testimony meets the requirements of Rule 702 to the extent

that he limits his testimony to identifying and explaining the similarities and dissimilarities

between the known exemplars and the questioned documents. FDE Rauscher is precluded from

rendering any ultimate conclusions on authorship of the questioned documents and is similarly

precluded from testifying to the degree of confidence or certainty on which his opinions are

based.”); United States v. Hines, 55 F. Supp. 2d 62, 67 (D. Mass. 1999) (holding that expert

testimony concerning the general similarities and differences between a defendant’s handwriting

exemplar and a stick up note was admissible but not the specific conclusion that the defendant was

the author).

123 See United States v. Green, 405 F. Supp. 2d 104, 107 (D. Mass. 2005). 

21
that the expert would be permitted to testify only that it was “more likely than

not” that recovered bullets and cartridge cases came from a particular weapon.124

“To the Exclusion of All Others”

Experts have frequently testified that they have made a match “to the

exclusion of all other firearms.”125

 This is simply another way of claiming

uniqueness. In United States v. Green,

126

 the court questioned such testimony: 

“[The expert] declared that this match could be made ‘to the exclusion of every

other firearm in the world.’ . . . That conclusion, needless to say, is extraordinary,

particularly given [the experts] data and methods.”127

 Further, in 2008, a year

before the NAS report on forensic science was issued, a different NAS report, one

on computerized ballistic imaging, addressed this issue. The report cautioned: 

“Conclusions drawn in firearms identification should not be made to imply the

presence of a firm statistical basis when none has been demonstrated.”

128

In

particular, that report was concerned about testimony cast “in bold absolutes”

such as that a match can be made to the exclusion of all other firearms in the

world: “Such comments cloak an inherently subjective assessment of a match

with an extreme probability statement that has no firm grounding and

unrealistically implies an error rate of zero.”129 Several courts are in accord.130

“Individualization” 

It is easier to identify what an expert should not say than to prescribe what

an expert may legitimately opine at trial. Some scholars have questioned whether

individualization is even achievable.131 Other scholars do not accept this “radical

124 United States v. Glynn, 578 F. Supp. 2d 567, 575 (S.D. N.Y. 2008).

125 See FBI HANDBOOK OF FORENSIC SCIENCES 57 (rev. ed. 1994).

126 United States v. Green, 405 F. Supp. 2d 104 (D. Mass. 2005).

127 Id. at 107 (citations omitted).

128 NATIONAL RESEARCH COUNCIL, NATIONAL ACADEMY OF SCIENCES, BALLISTIC

IMAGING 82 (2008) (emphasis in original). 

129 Id.

130 See United States v. Alls, slip opinion, No. CR2-08-223(1) (S.D. Ohio Dec. 7,

2009) (“[T]his Court follows the approach taken by Glynn, Monteiro, Green, Diaz and Mouzone,

and places a limitation on [the expert] testimony. Although [the expert] may testify as to her

methodology, case work, and observations in regards to the casing comparison she performed for

this case, she may not testify as to her opinion on whether the casings are attributable to a single

firearm to the exclusion of all other firearms. Such testimony would be misleading and prejudicial

given the inherent subjectivity in Firearm and Toolmark Identification.”); United States v. Diaz,

No. CR 05-00167 WHA, 2007 WL 485967, at *1 (N.D. Cal. Feb. 12, 2007). 

131 Michael J. Saks & Jonathan J. Koehler, The Individualization Fallacy in

Forensic Science Evidence, 61 VAND. L. REV. 199, 205 (2008) (“The concept of

‘individualization,’ which lies at the core of numerous forensic science subfields, exists only in a

metaphysical or rhetorical sense. It has no scientific validity, and it is sustained largely by the

22
skepticism” and believe that such an approach would mislead the jury in the other

direction — by vitiating the probative value of the evidence.132 This position,

however, does not endorse the overstatements described above. Nor does it

minimize the risk of misleading the jury or give the expert carte blanche authority: 

Let us assume that the jury gets the message — a match is not an

absolute identification. Can the criminalist do something more to explain

its probative value? Obviously, this depends on what is known about the

frequency of the identifying trait in the relevant population. Are the

features very common, rarely seen, or somewhere in between? There will

be occasions when such qualitative testimony is reasonable. When no

duplicates have been seen after systematic, careful and (one hopes)

representative studies, a criminalist determined to refer to uniqueness

might even assert that a trait is either unique or very rare in a population.133

F. “Consistent With”

 The phrase “consistent with” has long been recognized as problematic. 

The controversial Sacco and Vanzetti case, in which the defendants were executed

for a murder during a payroll robbery in 1921, is illustrative. Firearms

identification evidence played a critical role in this prosecution. After reviewing

the case, Professors Morgan and Joughin, wrote: 

On October 23 Captain Proctor made an [post-trial] affidavit indicating

that he had repeatedly told [the prosecutor] that he would have to answer

in the negative if he were asked whether he had found positive evidence

that the fatal bullet had been fired from Sacco’s pistol. The statement

which Proctor made on the witness stand was: “My opinion is that it is

consistent with being fired by that pistol.”134

What does the term “consistent with” mean in hair analysis? The

probative value of this conclusion would, of course, vary if only a hundred people

had microscopically indistinguishable hair as opposed to several million. The

crime scene hair could have come from 5 other persons — or 10, 50, 100, 500,

1,000, 100,000, and so forth. As one hair examiner wrote: “If a pubic hair from

the scene of a crime is found to be similar to those from a known source, [the

faulty logic that equates infrequency with uniqueness.”).

132 David H. Kaye, Probability, Individualization and Uniqueness in Forensic

Science Evidence: Listening to the Academies, 75 BROOK. L. REV. 1163, 1185 (2010). 

133 Id. at 1180. 

134 LOUIS JOUGHIN & EDMUND M. MORGAN, THE LEGACY OF SACCO & VANZETTI

15 (1948). These authors concluded: “In effect it is an act of self-impeachment by one of the

experts who testified for the prosecution at the Dedham trial.” Id.

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courts] do not know whether the chances that it could have originated from

another source are one in two or one in a billion.”135

G. “Match”

Professor Berger put it this way:

We allow eyewitnesses to testify that the person fleeing the scene wore a

yellow jacket and permit proof that a defendant owned a yellow jacket

without establishing the background rate of yellow jackets in the

community. Jurors understand, however, that others than the accused own

yellow jackets. When experts testify about samples matching in every

respect, the jurors may be oblivious to the probability concerns if no

background rate is offered, or may be unduly prejudiced or confused if the

probability of a match is confused with the probability of guilt, or if a

background rate is offered that does not have an adequate scientific

foundation.136

VII. DECLARATION OF EXPERTISE

ABA Civil Trial Practice Standard 14 provides: “The court should not, in

the presence of the jury, declare that a witness is qualified as an expert or to

render an expert opinion, and counsel should not ask the court to do so.”137 This

policy was later extended to criminal cases. As one court remarked, 

Great care should be exercised by a trial judge when the determination has

been made that the witness is an expert. If the jury is so informed such a

conclusion obviously enhances the credibility of that witness in the eyes of

the jury. All such ruling should be made outside the hearing of the jury

and there should be no declaration that the witness is an expert.138

In 1994, Judge Richey recommended this approach, noting that such a practice

“ensures that trial courts do not inadvertently put their stamp of authority” on a

135 B.D. Gaudette, Probabilities and Human Pubic Hair Comparisons, 21 J.

FORENSIC SCI. 514, 514 (1976). 

136 Margaret A. Berger, Procedural Paradigms for Applying the Daubert Test, 78

MINN. L. REV. 1345, 1357 (1994).

137 ABA CIVIL TRIAL PRACTICE STANDARD 14 (2007). 

138 Luttrell v. Commonwealth, 952 S.W.2d 216, 218 (Ky. 1997). See also United

States v. Laurienti, 611 F.3d 530, 547 (9th Cir. 2010) (“To the extent that Defendants argue that

the district court abused its discretion by failing to describe Meyer as an ‘expert’ in front of the

jury, we disagree. The determination that a witness is an expert is not an express imprimatur of

special credence; rather, it is simply a decision that the witness may testify to matters concerning

‘scientific, technical, or other specialized knowledge.’ Fed.R.Evid. 702.”).

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witness’ opinion, and protects against the jury’s being “overwhelmed by the socalled ‘experts.’”139

IX. ATTORNEY COMPETENCE

A. Ethical Duty

Perhaps the most basic of all professional ethical precepts is competence. 

Indeed, it appears as the first of the ABA Model Rules of Professional Conduct: 

“A lawyer shall provide competent representation to a client. Competent

representation requires the legal knowledge, skill, thoroughness and preparation

reasonably necessary for the representation.”140 An accompanying comment

explains that relevant factors in determining whether a lawyer acts competently

include “the relative complexity and specialized nature of the matter.”141

Thus, questions of competence under Model Rule 1.1 can be broken down

into issues of expertise and preparation. The first — which the rule refers to with

the words “knowledge” and “skill” — deals with the capability of a lawyer to

handle a particular representation. The second — which the rule refers to with the

words “thoroughness and preparation” — deals with the time and effort the

lawyer invests in preparing the case. In other words, a lawyer may violate the

duty of competence by lacking sufficient knowledge of a particular area of law. 

Or, even if the lawyer has sufficient expertise, the lawyer may violate the duty of

competence by failing to investigate and prepare the case sufficiently. 

No attorney can try criminal cases today without a grounding in forensic

evidence. The ABA has adopted the following recommendations: (1) “Training

in forensic science for attorneys should be made available at minimal cost to

ensure adequate representation for both the public and defendants,” and (2)

“Counsel should have competence in the relevant area or consult with those who

do where forensic evidence is essential in a case.”142

B. Right to Effective Assistance of Counsel

In addition, the Sixth Amendment right to counsel includes the right to

139 Charles Richey, Proposals to Eliminate the Prejudicial Effect of the Use of the

Word “Expert” Under the Federal Rules of Evidence in Civil and Criminal Jury Trials, 154

F.R.D. 537, 559 (1994).

140 ABA MODEL RULES OF PROF’L CONDUCT R. 1.1. 

141 Id. at R. 1.1 cmt. 1.

142 REPORT OF THE ABA CRIMINAL JUSTICE SECTION’S AD HOC INNOCENCE

COMMITTEE TO ENSURE THE INTEGRITY OF THE CRIMINAL PROCESS, ACHIEVING JUSTICE: FREEING

THE INNOCENT, CONVICTING THE GUILTY 47 (Paul C. Giannelli & Myrna Raeder eds. 2006).

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effective assistance of counsel.143

 The Supreme Court has decided several recent

cases on the subject. In Harrington v. Richter,144the Court wrote: “Criminal

cases will arise where the only reasonable and available defense strategy requires

consultation with experts or introduction of expert evidence.”145 In Hinton v.

Alabama,

146

 the Court found counsel ineffective for failing to understand how to

apply for funds in order retain a defense expert. In many of the cases cited earlier,

defense counsel failed to provide adequate representation.

X. CLOSING ARGUMENT

Properly presented evidence may become misleading due to its

characterization in closing argument to the jury.

147

 Williamson (discussed above) 

exemplifies this issue. In summation, the prosecutor claimed: “[T]here’s a

match.”148 Even the state court misinterpreted the evidence, writing that the “hair

evidence placed [petitioner] at the decedent’s apartment.”149 As noted above,

using the term “match” — without further explication — may be misleading. 

Similarly, in People v. Linscott150 the Illinois Supreme Court found that the

prosecutor improperly argued that hairs collected from the victim’s apartment

“were conclusively identified as coming from defendant’s head and pubic region. 

There simply was not testimony at trial to support these statements. In fact, [the

prosecution experts] and the defense hair expert . . . testified that no such

identification was possible.”151 Linscott was subsequently exonerated by DNA

evidence.152

In United States v. Hebshie,

153

 an arson case involving an accelerant143 See Evitts v. Lucey, 469 U.S. 387, 396 (1985) (“[A] party whose counsel is

unable to provide effective representation is in no better position than one who has no counsel at

all.”).

144 131 S. Ct. 770 (2011).

145 Id. at 788.

146 134 S. Ct. 1081 (2014).

147 See Darden v. Wainwright, 477 U.S. 168, 181-82 (1986) (“The prosecutors’

argument did not manipulate or misstate the evidence . . . .”). 

148 904 F. Supp. at 1557.

149 Williamson v. State, 812 P.2d 384, 397 (Okla. Crim. App. 1991).

150 566 N.E.2d 1355 (Ill. 1991).

151 Id. at 1359. 

152 EXONERATED BY SCIENCE, supra note 41, at 65 (“The State’s expert on the hair

examination testified that only 1 in 4,5000 person would have consistent hairs when tested for 40

different characteristics. He only testified between 8 and 12 characteristics, however, and could no

remember which ones. The appellate court ruled on July 29, 1987, that his testimony coupled with

the prosecution’s use of it at closing arguments, constituted denial of a fair trial.”).

153 754 F. Supp. 2d 89 (D. Mass. 2010).

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detecting dog (Billy), the court found the closing argument misleading. The

“government’s closing argument . . . dramatically overstated Billy’s

significance.”154 In its summation, the prosecutor “placed special emphasis on

Billy the dog, implying that she had alerted to one space to the exclusion of all the

others — which was not the case. Billy had not been shown ‘all other’ areas.”155

Defense counsel failed to object. For this and other lapses, the court found that

the defense counsel rendered ineffective assistance.

The ABA Criminal Justice Standards state that “[i]t is unprofessional

conduct for the prosecutor intentionally to misstate the evidence or mislead the

jury as to the inferences it may draw.”156

 The same rule applies to the defense.157

154 Id. at 95. See also Mitchell v. Gibson, 262 F.3d 1036, 1064 (10th Cir. 2001)

(Expert’s misconduct compounded by “the prosecutor, whom the district court found had ‘labored

extensively at trial to obscure the true DNA test results and to highlight [the expert’s] test results,’

and whose characterization of the FBI report in his closing argument was ‘entirely unsupported by

evidence and . . . misleading.’”).

155 Id. at 105.

156 ABA Standard 5.8(a), supra note 22. 

157 Id. Standard 4-7.7.

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