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State of Nebraska, appellee, v. 

Charles M. Simmer, appellant.

___ N.W.2d ___

Filed November 1, 2019. No. S-18-500.

1. Expert Witnesses: Appeal and Error. The standard for reviewing the 

admissibility of expert testimony is abuse of discretion.

2. Judgments: Expert Witnesses: Words and Phrases. An abuse of discretion in the trial court’s determination under Daubert v. Merrell Dow 

Pharmaceuticals, Inc., 509 U.S. 579, 113 S. Ct. 2786, 125 L. Ed. 2d 469 

(1993), and Schafersman v. Agland Coop, 262 Neb. 215, 631 N.W.2d 

862 (2001), occurs when a trial court’s decision is based upon reasons 

that are untenable or unreasonable or if its action is clearly against justice or conscience, reason, and evidence.

3. Courts: Expert Witnesses. Under the Daubert v. Merrell Dow 

Pharmaceuticals, Inc., 509 U.S. 579, 113 S. Ct. 2786, 125 L. Ed. 2d 469 

(1993), and Schafersman v. Agland Coop, 262 Neb. 215, 631 N.W.2d 

862 (2001), framework, the trial court acts as a gatekeeper to ensure the 

evidentiary relevance and reliability of an expert’s opinion.

4. Trial: Expert Witnesses: Intent. The purpose of the gatekeeping 

function is to ensure that the courtroom door remains closed to “junk 

science” that might unduly influence the jury, while admitting reliable 

expert testimony that will assist the trier of fact.

5. Trial: Expert Witnesses. A trial court can consider several nonexclusive factors in determining the reliability of an expert’s opinion: (1) 

whether a theory or technique can be (and has been) tested; (2) whether 

it has been subjected to peer review and publication; (3) whether, in 

respect to a particular technique, there is a high known or potential 

rate of error; (4) whether there are standards controlling the technique’s 

operation; and (5) whether the theory or technique enjoys general 

acceptance within a relevant scientific community.

6. ____: ____. Once the reasoning or methodology of an expert opinion 

has been found to be reliable, the court must determine whether the 

Nebraska Supreme Court Online Library

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expert’s reasoning or methodology can be properly applied to the facts 

in issue.

Appeal from the District Court for Douglas County: Thomas 

A. Otepka, Judge. Affirmed.

Thomas C. Riley, Douglas County Public Defender, for 

appellant.

Douglas J. Peterson, Attorney General, and Melissa R. 

Vincent for appellee.

Heavican, C.J., Miller-Lerman, Cassel, Stacy, Funke, 

Papik, and Freudenberg, JJ.

Papik, J.

Charles M. Simmer appeals his conviction for first degree 

murder. DNA evidence presented at Simmer’s jury trial linked 

him to the crime. The sole issue presented by this appeal is 

whether the district court erred in admitting DNA analysis conducted by using TrueAllele probabilistic genotyping software, 

over Simmer’s Daubert/Schafersman challenges. Finding no 

abuse of discretion, we affirm.

I. BACKGROUND

1. Overview

On November 3, 2007, Simmer’s aunt, Joy Blanchard, was 

murdered in her home. She was discovered lying face down on 

the floor with two knives protruding from her neck. Close by 

was a spindle broken from the nearby bannister. An autopsy 

revealed the cause of death to be blunt force trauma and stab 

wounds to the head and neck.

When law enforcement processed the crime scene, they 

swabbed several items for DNA, including the spindle, the 

handles on both knives, and the interior doorknob on the front 

door of the residence. DNA testing and analysis conducted in 

2015 and 2016 indicated the presence of Simmer’s DNA on 

one of the knife handles and the interior doorknob.
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On June 7, 2016, Simmer was charged by information 

in Douglas County District Court with one count of first 

degree murder, a Class IA felony. Prior to trial, Simmer filed 

a motion in limine asserting a challenge to DNA analysis 

performed by Cybergenetics, Inc., which challenge was pursuant to Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 

U.S. 579, 113 S. Ct. 2786, 125 L. Ed. 2d 469 (1993), and 

Schafersman v. Agland Coop, 262 Neb. 215, 631 N.W.2d 862 

(2001) (Daubert/Schafersman). He sought to preclude the 

State from introducing at trial “any and all testimony concerning DNA testing and the results of said testing,” including 

“identification” and “comparison” of DNA testing. Simmer 

alleged that the reliability of the theories, techniques, and procedures used by the State’s experts had not been established 

and that the proposed testimony was “based on insufficient 

facts and data.” Hearings were held on the motion, and the 

district court overruled it.

At the subsequent jury trial, Simmer preserved the Daubert/

Schafersman challenges raised in his pretrial motion. He 

lodged a continuing objection when Dr. Mark Perlin, the chief 

scientist and executive officer at Cybergenetics, was called 

to testify about TrueAllele probabilistic genotyping and its 

application in this case. The district court overruled the objection. The jury heard DNA evidence and other circumstantial evidence connecting Simmer to Blanchard’s murder, and 

Simmer was convicted of the crime charged and sentenced to 

life imprisonment.

The sections below summarize the Daubert/Schafersman

proceedings and the relevant evidence at trial.

2. Daubert/Schafersman Proceedings

At pretrial proceedings on Simmer’s motion in limine, the 

district court received exhibits and heard expert testimony 

about DNA evidence from three witnesses. Generally, Mellissa 

Helligso’s testimony provided context for Perlin’s testimony 

about Cybergenetics’ TrueAllele probabilistic genotyping 
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program. Simmer elicited testimony from Nathaniel Adams to 

challenge TrueAllele’s methodology.

(a) Testimony of Helligso

Helligso, a forensic DNA analyst employed by the University 

of Nebraska Medical Center (UNMC), testified about the DNA 

tests that she performed in this case. Helligso explained the 

process by which an autosomal DNA profile is obtained and 

analyzed. Upon receiving evidence containing biological material, she extracts the DNA, quantifies and amplifies it, and ultimately runs it through a genetic analyzer. The genetic analyzer 

generates a DNA profile that can then be compared to DNA 

from known individuals. Typically, the analysis is limited to 

specific locations in the DNA and does not include a full profile. If she identifies consistencies between the evidence profile 

and the known individual’s profile, she will “generate a statistic to show the likelihood of that match happening.”

Helligso also explained the difference between autosomal 

DNA and Y-STR DNA. Humans have 23 pairs of chromosomes 

with each pair consisting of one each from the father and 

mother. The term “allele” describes the varying forms of a gene 

that can be specific to an individual but found for everyone at 

the same place in the same chromosome. Differences in alleles 

at predetermined chromosome locations, referred to as “loci,” 

define a person’s DNA profile and can be used for comparison 

with evidence samples.

Helligso explained that autosomal DNA is composed of 

DNA inherited from both parents. Y-STR DNA, on the other 

hand, involves only the Y chromosome, which is found only in 

males and is passed from father to son. Because all males in 

the same family have the same Y-STR DNA, it cannot identify 

a particular male within that family and is less discriminating 

than autosomal DNA. In Y-STR DNA testing, a DNA extract is 

amplified with a particular “kit” that only looks at the Y-STR 

locations found on the Y chromosome.

In this case, among the items that Helligso received in 

2007 were swabs obtained from one of the knife handles and 
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the spindle. Y-STR DNA testing of both items disclosed the 

presence of two Y chromosomes, indicating a mixture of two 

males. Simmer could not be excluded as the major male contributor in either sample, but neither could his brother, since 

they share the same Y chromosome. The probability of a match 

was stronger on the knife handle than on the spindle.

In November 2015, Helligso received several additional 

items for testing, including a swab from the interior doorknob 

on the front door to Blanchard’s residence. Helligso determined the sample contained autosomal DNA from at least two 

individuals. Neither Blanchard nor Simmer could be excluded 

as full contributors on the doorknob, and “[t]he probability of 

a random individual matching a DNA profile within the mixture, given that . . . Simmer expresses such a profile, [was] 1 

in 357 million . . . for Caucasians, 1 in 844 million . . . for 

African Americans, and 1 in 2.37 billion . . . for American 

Hispanics.”

Helligso suggested sending her work to Perlin at 

Cybergenetics for additional analysis. To provide the background for that decision, Helligso explained the process by 

which a DNA profile is obtained and analyzed and the significance of data “thresholds.” She stated that for any type 

of testing done by UNMC, the laboratory must go through a 

validation process:

[O]ne of the things that you have to establish is your 

threshold, which is the height at which, in your laboratory, you can determine the difference between what 

would be considered a real peak or real allele and background noise of the instrumentation, because every instrument has background noise just by the technology in 

which it works. And so every laboratory, for their own 

instrumentation, has to determine where that cutoff lies 

within the data.

. . . .

. . . In our laboratory, the threshold for autosomal, and 

I believe for Y-STR in this case as well, was set at 50 
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[relative fluorescence units (RFU)]. So any peak that is 

below 50 RFU does not get labeled by the software program that we have, so then we, in general, do not look at 

those peaks. They can be considered if you’re trying to 

determine if you have a mixture, but, in general, no, we 

don’t look at those peaks then.

Helligso explained that at UNMC, none of the data below the 

threshold is used in her statistical calculations.

Helligso testified that Cybergenetics had developed a software program that is not bound by data thresholds. Using 

a series of mathematical calculations, the software analyzes 

every peak to determine whether it is “an artifact [or] a real 

allele.” Helligso also testified that Perlin does not retest the 

evidence; rather, his software simply uses all the data compiled 

by the laboratory during its analysis. Helligso testified that 

the human brain could perform the same calculations as the 

software, but it would require “an extreme amount of time.” 

She stated that it makes sense to use software that performs the 

necessary calculations quickly and accurately.

Helligso testified that probabilistic genotyping has “definitely been a hot topic for a couple of years now.” When 

Helligso was asked whether there was some dispute about 

the general acceptance of Perlin’s approach in the broader 

scientific community, Helligso replied, “[I]f you [had] asked 

me that question six or seven years ago, I would have agreed, 

but I would say now within the last five years that, in general, the community is — is agreeing that these types of 

software programs are necessary.” The number of people who 

do not agree are “becoming fewer and fewer.” She pointed 

out that TrueAllele addresses a need in the DNA analysis 

community by facilitating the use of all of the DNA data 

to calculate a “good statistic.” Helligso noted that the accuracy of TrueAllele software had been tested over at least 10 

years with thousands of known profiles with an “extremely 

high success rate.” She also noted that a similar program, 

“STRmix,” is “being highly touted by the FBI and the 
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national government” and “has kind of taken off to where lots 

of laboratories have those.”

(b) Testimony of Perlin

As noted above, Perlin is the chief scientist and executive 

officer at Cybergenetics, a bioinformation company. He testified about his company’s software, TrueAllele, and its application in Simmer’s case.

Perlin explained that TrueAllele is designed to separate the 

various contributors to DNA samples processed by crime laboratories and assess the likelihood that a contributor matches a 

known sample. Like Helligso, Perlin testified that TrueAllele’s 

method of analysis differs from traditional DNA analysis performed by humans in that TrueAllele does not utilize thresholds, which exclude or discard data that falls below a predetermined level. Instead, it analyzes all of the data, taking into 

account peak heights and other patterns. According to Perlin, 

TrueAllele yields more accurate results, that is, it can produce 

a stronger “match statistic” or, alternatively, exclude an individual who may have otherwise been included.

Crime scene samples can consist of very small amounts of 

DNA, incomplete DNA, and DNA from more than one contributor. Using a series of complex probability equations and 

statistical sampling, TrueAllele tries out thousands of possible 

explanations, or possible genotypes, for the crime scene data, 

and calculates the probability of each explanation. Those that 

explain the data well generate higher probability, while those 

that explain the data not as well, or not at all, generate lower 

probability. This process suggests genotypes and their probabilities at every genetic location for each contributor to the 

crime scene sample.

Perlin testified that TrueAllele ultimately infers a genotype, 

or DNA barcode, for each contributor to the crime scene evidence, which is a probability distribution over possible allele 

pairs, and then calculates the probability that an inferred 

genotype matches (1) the suspect and (2) a random person in 
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the population. The program then divides the former by the 

latter to generate a likelihood ratio or “match statistic.” The 

match statistic answers the question: “How much more does 

the suspect match the evidence at this location than a random person?”

Perlin explained that TrueAllele is more objective than the 

traditional method, because the computer analyzes the data 

without comparing it to a known sample from a suspect or 

“anybody’s preferred answer.” A suspect’s genotype is not 

given to the computer until it calculates the match statistic.

Perlin recounted the development of TrueAllele. Perlin, who 

has a bachelor’s degree in chemistry, is a doctor of medicine, 

and has Ph.D.’s in mathematics and computer science, began 

using computers to interpret genetic information in the early 

1990’s while working on the Human Genome Project. At that 

time, he became involved in the development of software 

that would enable a computer to understand and eliminate 

artifacts in DNA data. He continued that work after founding 

Cybergenetics in 1994 and published his first article on the 

subject in 1995. Over the course of 15 years, Perlin developed TrueAllele. TrueAllele is based on “Bayesian” probability modeling and “Markov chain Monte Carlo” statistical 

sampling, both widely accepted in the relevant communities 

for decades. Perlin testified that TrueAllele uses mathematics and algorithms developed 20 years prior to trial, with the 

“core math of calculating genotypes [remaining] the same 

since 2008.”

Perlin testified that TrueAllele is widely used. He stated 

that he and his company have been extensively involved in 

educating and training laboratory analysts to use TrueAllele. 

Perlin testified that at least 10 laboratories around the country have used TrueAllele, 7 of them regularly, and have done 

their own internal validations of the software. TrueAllele had 

conducted analyses in at least 500 cases in 37 states, though 

not all of the analyses were used in court. Further, TrueAllele 

had been used to analyze small quantities of damaged DNA 
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from thousands of human remains to help identify victims of 

the September 11, 2001, terrorist attack on the World Trade 

Center. Perlin also testified that TrueAllele had been used 

by the DNA group at the National Institute of Standards and 

Technology, a part of the U.S. Department of Commerce that 

“create[s] resources for the forensic community in the U.S. 

and the world that are standards.” He stated that the national 

institute had used TrueAllele to create standards for a DNA 

mixture against which laboratories could check their equipment and methods.

Perlin testified that TrueAllele had been used in court proceedings. He stated that he had testified in at least 10 admissibility hearings and that no court had found his testimony to be 

inadmissible. The district court received nine trial court admissibility rulings from other jurisdictions in the United States 

allowing TrueAllele evidence, five of them applying a Daubert

standard. Perlin testified that Cybergenetics does work for 

both the prosecution and the defense. He noted that TrueAllele 

had been used in more than 10 cases by the Innocence Project, 

a group that seeks to exonerate the wrongly convicted. Perlin 

testified that Cybergenetics screens DNA from any group at no 

cost and only charges for additional services, such as a written 

report or testimony. He also stated that TrueAllele provides 

the opportunity for any group to run its software for free to 

independently confirm results and that results could also be 

confirmed through competing software.

Perlin also testified concerning approval of TrueAllele by 

the Scientific Working Group on DNA Analysis Methods 

(SWGDAM). SWGDAM is composed of highly respected 

individuals in the DNA analysis community who author guidelines for DNA analysis that are often adopted by accrediting 

agencies. SWGDAM approved the use of probabilistic genotyping software in 2010, as long as it had been validated and 

documented. And in 2015, SWGDAM issued guidelines for 

validating probabilistic genotyping programs, centering on laboratory validation, sensitivity, specificity, and reproducibility. 
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Sensitivity reflects the extent to which interpretation identifies the correct person, specificity reflects the extent to which 

interpretation does not identify the wrong person, and reproducibility reflects the extent to which interpretation consistently gives the same answer to the same question. According 

to Perlin’s testimony and documentary evidence generated by 

Cybergenetics, TrueAllele complies with those guidelines.

The district court received numerous validation studies of 

TrueAllele. Perlin described validation studies as “tests that 

are done where known data is put into a method, like a computer program for calculating match statistics, and the results 

are assessed on 10 to 100 samples, depending on the study, 

and its performance is measured, along with error rates.” 

According to Perlin, 34 studies conducted by the TrueAllele 

laboratory and other crime laboratories and groups had shown 

that TrueAllele produces accurate and reliable results with 

“no surprises.”

Perlin stated that typically in the field of science, a method 

like TrueAllele would be featured in only one peer-reviewed 

publication. However, of the 34 validation studies in evidence, 7 studies had been published in peer-reviewed journals and 6 of the 7 studies in evidence identified Perlin as a 

coauthor.

Perlin testified that TrueAllele’s error rates had been tested 

multiple times in two ways, which Perlin described in detail. 

First, error rates had been tested through validation studies of 

large ensembles of “real,” “less pristine” samples from casework to demonstrate how the system works in practice. And 

second, error rates were tested by the application of information theory to determine the expected distribution of match 

statistics from one evidence genotype of known composition 

to “provide information about a sample in a case and what 

the error rate would be for a particular match statistic.” Of the 

seven peer-reviewed validation studies, four used laboratory 

samples of known composition and three drew from less pristine crime scene data.
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In this case, Perlin used TrueAllele to analyze the data 

from UNMC and calculated likelihood ratios for Simmer on 

both the knife handle and the doorknob. According to Perlin’s 

analysis, the match between the knife handle and Simmer was 

3.71 thousand times more probable than a coincidental match 

to an unrelated person, while the match between the doorknob 

and Simmer was 4.22 quintillion times more probable than a 

coincidental match to an unrelated person. Perlin also calculated likelihood ratios for Simmer’s brother as to both items; 

however, his ratios were exclusionary.

Other portions of Perlin’s testimony are mentioned, as relevant, in the analysis section below.

(c) Testimony of Adams

Adams has a bachelor’s degree in computer science and is 

employed by a company that “consult[s] with lawyers to help 

them understand what kind of [DNA] testing was conducted, 

whether there are any issues with that testing with the analysis 

or interpretation of the data.” The company reviews “standard 

operating procedures, validation studies of the testing laboratories, [and] relevant literature in the forensic DNA field.” 

Adams’ duties involve the review of electronic data generated 

during the course of forensic DNA testing and case files from 

criminal investigations involving DNA testing.

Adams’ testimony and written report expressed concerns 

about the validity of TrueAllele’s probabilistic genotyping program from a software engineering perspective. Adams’ primary 

objection to the software was that it had not been confirmed 

that the software does what Perlin says it does. He testified, 

“This is one of the major topics of verification and validation 

. . . in the field of software engineering. We need to demonstrate, not just assume or expect, that a program is operating as 

described . . . .”

Adams testified that the problem with probabilistic genotyping programs like TrueAllele is that “[t]he field of forensic 

DNA does not have any standards specific to it that software 
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must adhere to before it’s utilized in casework.” He stated 

that TrueAllele encompassed computing statistics and biology 

and that minimum quality assurance standards required a multidisciplinary, multiparty approach. Adams’ report acknowledged that the International Society of Forensic Genetics 

and SWGDAM had published guidance documents addressing 

validation of probabilistic genotyping software, but the field 

of forensic DNA analysis still lacked formal standards specific to its development and validation. His report observed 

that while there were no common software development standards for probabilistic genotyping, general software engineering industry standards and principles could be used to ensure 

correctness of the systems. However, this had not been done. 

As a result, he contended that defects may exist in the software and that their significance to its operation would persist undetected.

Adams noted that a program’s source code, the programming language instructing the computer what to do, can be 

inspected to determine whether the software program has been 

appropriately constructed. However, according to Adams, the 

TrueAllele source code had never been independently reviewed 

to determine whether the program operates as described by 

Perlin. The district court received evidence that Cybergenetics 

had recently decided to allow defense experts access to the 

TrueAllele source code, with limitations. In Adams’ view, 

reviewing the source code in the context of a particular case 

was prohibitive under the time and financial constraints of 

litigation, especially if certain software development materials 

were not involved in the review. In Adams’ opinion, review of 

the source code ought to occur over a long period prior to use 

in a criminal case.

Adams acknowledged that one way to determine whether 

a program works as intended is to use it, but that it was not 

the only way under software engineering general practices for 

quality assurance. He considered it “dangerous to allocate our 

only software defect detection efforts to the actual use of that 
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software” because of the significant impact latent defects could 

have. Adams testified that TrueAllele had achieved only the 

“illusion of validation” because it had not been validated in the 

domain of software engineering. And while he also acknowledged that TrueAllele had been developed over a period of several years before it was ever used in a criminal case, he stated 

that he still had concerns about it since he “[didn’t] know what 

defect prevention or mitigation strategies were employed during that time.”

In addition, Adams’ report questioned validation studies of 

the quantitative likelihood ratios generated by probabilistic 

genotyping “because no knowable correct output exists for 

any given input, against which the system’s behaviors could 

be tested.” Adams explained that “we can’t know exactly what 

likelihood ratio should be developed, even if we know the 

inputs to the systems, the genotypes of the true contributors.”

Adams also expressed concern about the accuracy of likelihood ratios in general, even with known contributors, and 

stated that while he also has concerns about the accuracy of 

traditional DNA analysis, he prefers it to computer programs 

because it is more transparent and its calculations “can be 

replicated by anybody with a pocket calculator or an Excel 

spreadsheet.”

(d) Motion in Limine Overruled

Following the hearing, the district court overruled Simmer’s 

motion in limine. It found Perlin to be an expert in the field 

of probabilistic genotyping. The district court further found 

that the TrueAllele evidence was relevant and that it would 

be helpful to the finder of fact in this case. The district court 

applied the Daubert/Schafersman analytical framework and 

determined the methodology of TrueAllele probabilistic genotyping was reliable, noting that the Daubert test was flexible 

and that not every factor need be considered. We summarize the district court’s ruling in detail in the analysis section below.
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3. Relevant Evidence at Trial

At trial, the State presented DNA evidence connecting 

Simmer to the crime scene. Helligso and Perlin both gave 

testimony consistent with their testimony at the hearing on 

Simmer’s motion in limine. Helligso testified that her analysis showed that neither Simmer nor his brother could be 

excluded as the major male contributor to DNA on the spindle 

and the knife handle. As for the DNA on the interior doorknob, Helligso’s analysis determined that the sample contained a mixture of at least two individuals and that neither 

Blanchard nor Simmer could be excluded as full contributors. She stated that the probability of a random individual 

matching a DNA profile within the mixture on the interior doorknob, given that Simmer expresses such a profile, 

was 1 in 357 million. Regarding the TrueAllele analysis 

of the evidence in this case, Perlin testified that the match 

between the knife handle and Simmer was 3.71 thousand 

times more probable than a coincidental match to an unrelated 

person, while the match between the doorknob and Simmer 

was 4.22 quintillion times more probable than a coincidental 

match to an unrelated person. As he did at the hearing on 

Simmer’s motion in limine, Perlin also described at trial how 

TrueAllele works.

In addition to DNA evidence, the State introduced other evidence linking Simmer to Blanchard’s murder. Although there 

was no direct evidence that Simmer had been at Blanchard’s 

residence on the night of the murder, from early on, he was 

a suspect in the police investigation. The State presented 

evidence at trial that Simmer had not been to Blanchard’s 

residence during the 21⁄2 years prior to Blanchard’s murder; 

that Simmer had misinformed police about his whereabouts 

during the timeframe of Blanchard’s murder; that 2 days after 

the murder, Simmer tried to conceal injuries to his hands from 

police; that he physically resisted providing a court-ordered 

DNA sample; and that about 3 months after the murder, he had 

confided in a friend about stabbing someone to death.
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II. ASSIGNMENTS OF ERROR

Simmer assigns that the district court committed reversible 

error in rejecting his Daubert/Schafersman challenge and in 

allowing the State to present Perlin’s expert opinion testimony 

and evidence concerning Perlin’s conclusions on DNA evidence connecting Simmer to the crime scene.

III. STANDARD OF REVIEW

[1,2] The standard for reviewing the admissibility of expert 

testimony is abuse of discretion. State v. Tucker, 301 Neb. 856, 

920 N.W.2d 680 (2018). An abuse of discretion in the trial 

court’s Daubert/Schafersman determination occurs when a trial 

court’s decision is based upon reasons that are untenable or 

unreasonable or if its action is clearly against justice or conscience, reason, and evidence. State v. Hill, 288 Neb. 767, 851 

N.W.2d 670 (2014).

IV. ANALYSIS

Simmer’s sole assignment of error challenges the admission 

of TrueAllele probabilistic genotyping evidence linking him to 

the crime scene. While Simmer’s appeal focuses exclusively 

on the admission of this evidence, his arguments fall into two 

different categories within the Daubert/Schafersman analysis. 

Simmer makes a number of arguments aimed at the general 

reliability of TrueAllele. Other arguments focus on whether 

TrueAllele, even if generally reliable, was properly applied to 

the facts in this case. After briefly reviewing the basic governing legal principles, we will proceed to analyze Simmer’s arguments in turn.

1. Daubert/Schafersman Standards

The Nebraska Evidence Rules provide: “If scientific, technical, or other specialized knowledge will assist the trier of 

fact to understand the evidence or to determine a fact in issue, 

a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form 

of an opinion or otherwise.” Neb. Evid. R. 702, Neb. Rev. 
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Stat. § 27-702 (Reissue 2016). Perlin’s qualifications are not 

at issue in this appeal. Rather, Simmer argues that the State 

failed to demonstrate that the TrueAllele evidence was admissible under the Daubert/Schafersman framework and that the 

district court therefore abused its discretion in allowing it in 

evidence. See State v. Casillas, 279 Neb. 820, 782 N.W.2d 882 

(2010) (burden is on proponent of evidence to establish admissibility under Daubert/Schafersman).

[3,4] Under the Daubert/Schafersman framework, the trial 

court acts as a gatekeeper to ensure the evidentiary relevance 

and reliability of an expert’s opinion. Hemsley v. Langdon, 299 

Neb. 464, 909 N.W.2d 59 (2018). The purpose of this gatekeeping function is to ensure that the courtroom door remains 

closed to “junk science” that might unduly influence the jury, 

while admitting reliable expert testimony that will assist the 

trier of fact. State v. Herrera, 289 Neb. 575, 856 N.W.2d 

310 (2014). The Daubert/Schafersman standards require proof 

of the scientific validity of principles and methodology utilized by an expert in arriving at an opinion. See Hemsley v. 

Langdon, supra.

[5] A trial court can consider several nonexclusive factors in determining the reliability of an expert’s opinion: (1) 

whether a theory or technique can be (and has been) tested; (2) 

whether it has been subjected to peer review and publication; 

(3) whether, in respect to a particular technique, there is a high 

known or potential rate of error; (4) whether there are standards controlling the technique’s operation; and (5) whether 

the theory or technique enjoys general acceptance within a 

relevant scientific community. State v. Braesch, 292 Neb. 

930, 874 N.W.2d 874 (2016). A trial court may consider one 

or more of these factors when doing so will help determine 

that testimony’s reliability, but the test of reliability is “‘flexible’” and the list of specific factors neither necessarily nor 

exclusively applies to all experts or in every case. See Kumho 

Tire Co. v. Carmichael, 526 U.S. 137, 141, 119 S. Ct. 1167, 

143 L. Ed. 2d 238 (1999), quoting Daubert v. Merrell Dow 
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Pharmaceuticals, Inc., 509 U.S. 579, 113 S. Ct. 2786, 125 L. 

Ed. 2d 469 (1993).

[6] Once the reasoning or methodology of an expert opinion 

has been found to be reliable, the trial court must determine 

whether the expert’s reasoning or methodology can be properly 

applied to the facts in issue. See State v. Edwards, 278 Neb. 

55, 767 N.W.2d 784 (2009).

2. General Reliability of 

TrueAllele Evidence

Simmer contends that the State failed to show the evidence generated by TrueAllele was sufficiently reliable under 

the Daubert/Schafersman framework. The district court concluded otherwise. In its order denying Simmer’s motion in 

limine, the district court first observed that TrueAllele had 

been tested by 34 validation studies and that it conforms to the 

SWGDAM guidelines for validating probabilistic genotyping 

systems. The district court next stated that TrueAllele had, on 

multiple occasions, been peer reviewed and subject to publication in an “unusually large number” of validation studies and 

that no significant scientific evidence suggested the reliability 

of TrueAllele had been refuted. Regarding TrueAllele’s error 

rate, the district court cited evidence that it had been assessed 

through validation studies and information theory comparing 

one evidence genotype to the expected distribution of match 

statistics. Finally, the district court determined that TrueAllele 

had been generally accepted in the relevant scientific community because it had been used in over two-thirds of the states 

in the United States, it had been used to identify mass casualty 

victims of the 2001 terrorist attack on the World Trade Center, 

it was used in over 10 cases by the Innocence Project, and 7 

crime laboratories were using the software regularly.

Simmer does not contest many of the facts underlying the 

district court’s analysis summarized above. Rather, he contends 

that the district court ignored other factors that call into question the reliability of TrueAllele.
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Simmer, for example, does not and cannot dispute the significant number of validation studies in the record concerning 

TrueAllele. Instead, he suggests that the validation studies 

must be discounted because Perlin is a coauthor of some of 

the publications and, as the owner of the company that owns 

TrueAllele, has a financial interest in seeing it found reliable. 

In other words, Simmer is contending that there are reasons 

to question Perlin’s credibility. Even assuming that is true, 

an attack on the credibility of an expert witness is not aimed 

at the expert’s reasoning or methodology and is thus not the 

proper basis for a Daubert/Schafersman challenge. See Smith v. 

Colorado Organ Recovery Sys., 269 Neb. 578, 694 N.W.2d 610 

(2005) (stating that challenge to expert witnesses’ credibility is 

not Daubert/Schafersman claim).

In any event, Perlin’s part in the validation studies was not 

as pervasive or unchecked as Simmer suggests. Perlin was 

not involved in 10 validation studies in the record. In addition, six of the studies in which he was listed as an author 

were published in peer-reviewed publications. As this court 

has previously recognized, “The reason that peer-reviewed 

publication is valuable is that it places research in the public 

domain and permits evaluation and criticism.” State v. Daly, 

278 Neb. 903, 914, 775 N.W.2d 47, 60 (2009). See, also, 

Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579, 

593, 113 S. Ct. 2786, 125 L. Ed. 2d 469 (1993) (“submission 

to the scrutiny of the scientific community is a component 

of ‘good science,’ in part because it increases the likelihood 

that substantive flaws in methodology will be detected”). 

Furthermore, Perlin was not the lone author on any of the 

published, peer-reviewed validation studies. That is, other 

members of the scientific community also staked their reputations on the reliability of TrueAllele. We see no basis to say 

that the district court abused its discretion by relying on the 

validation studies.

Simmer also argues that, apart from Perlin’s involvement in 

some of the validation studies, the studies themselves do not 
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demonstrate TrueAllele’s reliability. Here, Simmer relies heavily on the testimony of his expert, Adams. Adams acknowledged the studies in the record validating TrueAllele, but 

claimed that there is a difference between the “forensic DNA 

definition of validation and the software engineering definition of validation.” Adams emphasized that TrueAllele had not 

been tested from a software engineering perspective. In particular, Adams expressed concerns that the TrueAllele software 

source code had not been subjected to independent testing. He 

testified that without such a review, confirmation was lacking 

as to whether the TrueAllele software actually performs as 

described by Perlin.

We do not believe that the district court was required to 

find that TrueAllele had been validated “from a software 

engineering perspective” to find it reliable. In the Daubert/

Schafersman context, a trial court has discretion to decide what 

factors are reasonable measures of reliability in each case. See 

Zimmerman v. Powell, 268 Neb. 422, 684 N.W.2d 1 (2004), 

citing Kumho Tire Co. v. Carmichael, 526 U.S. 137, 119 S. 

Ct. 1167, 143 L. Ed. 2d 238 (1999) (Scalia, J., concurring). 

While a review of the TrueAllele source code might also have 

confirmed the reliability of TrueAllele, we cannot say that the 

district court abused its discretion by relying on the numerous 

validation studies confirming the reliability of TrueAllele by 

other means. See Com. v. Foley, 38 A.3d 882 (Pa. Super. 2012) 

(noting in Frye v. United States, 293 F. 1013 (D.C. Cir. 1923), 

analysis of TrueAllele that scientists can validate reliability of 

computerized process even if source code underlying process 

is unavailable to public). See, also, Edward J. Imwinkelried, 

Computer Source Code: A Source of the Growing Controversy 

Over the Reliability of Automated Forensic Techniques, 66 

DePaul L. Rev. 97 (2016).

Neither are we persuaded by Simmer’s argument that the 

validation studies are inadequate because the likelihood ratios 

generated by TrueAllele cannot be confirmed as accurate. Here 

again, Simmer relies heavily on Adams’ assertions. Adams 
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conceded that by running the TrueAllele software on known 

DNA profiles, one can determine whether TrueAllele accurately includes or excludes potential contributors. But Adams 

asserted that these same studies cannot confirm whether the 

specific likelihood ratios are accurate because there is no 

“knowable correct output.”

Perlin, however, testified that TrueAllele’s match statistics 

can be verified by comparing a broad range of match statistics 

to an expected distribution based on probability theory. At 

least one of the peer-reviewed validation studies did so and 

concluded that there was no significant difference between 

TrueAllele’s match statistics and a uniform distribution. The 

study concluded that this provided statistical support for the 

system’s accuracy. This method of testing may not have demonstrated to an absolute certainty that match statistics generated by TrueAllele are accurate, but a court performing a 

Daubert/Schafersman inquiry should not require absolute certainty. See, e.g., State v. Herrera, 289 Neb. 575, 856 N.W.2d 

310 (2014).

Finally, Simmer argues that the district court failed to 

acknowledge the existence of a California study which, Simmer 

contends, reported “significant errors” by TrueAllele. Brief for 

appellant at 21. This study, however, is not in the record in this 

case. Perlin referred to it in his testimony, but he also testified 

that it was a “procurement study,” which was never published, 

and that the laboratory conducting the study changed the 

parameters of TrueAllele so it did not work properly. We do 

not see how the district court could have abused its discretion 

by declining to rely on a study that was not in the record and 

was undermined by Perlin’s unrefuted testimony.

For the reasons we have explained, we disagree with 

Simmer’s argument that the district court ignored information it was required to consider in determining whether the 

TrueAllele evidence was reliable. Neither do we believe the 

district court’s ultimate conclusion that the State proved the 

reliability of TrueAllele amounted to an abuse of discretion. 
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The State adduced significant evidence that TrueAllele is reliable. The State presented Perlin’s testimony and copious documentary evidence describing TrueAllele’s methodology, which 

is based on established mathematical principles. SWGDAM 

has approved the use of validated and documented probabilistic 

genotyping software and provided guidelines for its validation. 

TrueAllele has complied with those guidelines: TrueAllele’s 

methodology has been repeatedly tested and validated in peerreviewed studies.

Even if TrueAllele has not garnered universal acceptance 

in the relevant scientific community, that does not automatically disqualify it for admission. See Epp v. Lauby, 271 Neb. 

640, 715 N.W.2d 501 (2006). The wide use of TrueAllele by 

government crime laboratories and other groups nationwide, 

Perlin’s participation in multiple lectures and conferences, and 

Helligso’s testimony that the scientific community had agreed 

in recent years that programs like TrueAllele are necessary, all 

tend to show that TrueAllele has been generally accepted in the 

relevant scientific community. Moreover, at least one appellate 

court opinion and several trial court orders in our record have 

found, based on similar evidence, that TrueAllele has gained 

such acceptance. See, e.g., Com. v. Foley, 38 A.3d 882 (Pa. 

Super. 2012) (rejecting challenge to TrueAllele, under Frye v. 

United States, 293 F. 1013 (D.C. Cir. 1923), standard, which 

requires general acceptance in relevant scientific community). 

See, also, e.g., State v. Wakefield, 47 Misc. 3d 850, 9 N.Y.S.3d 

540 (2015) (same).

3. Application of TrueAllele 

in This Case

As mentioned above, some of Simmer’s arguments on 

appeal are not directed to the TrueAllele methodology in a 

general sense, but instead attack the application of the methodology in this particular case. Specifically, Simmer contends 

that two reports, a 2015 validation study conducted by the 

Virginia Department of Forensic Science and a 2016 report by 
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the President’s Council of Advisors on Science and Technology 

(PCAST), suggest that TrueAllele could not be reliably applied 

to the particular facts in this case.

While Simmer criticizes the district court for not addressing 

his arguments based on these reports, we note that it is not 

clear that Simmer adequately raised these arguments in the 

district court. Simmer’s pretrial motion in limine challenged 

the reliability of TrueAllele evidence, but it did not specifically raise any concern about whether TrueAllele could properly be applied to the particular facts of this case. A challenge 

to the admissibility of evidence under Daubert/Schafersman

should take the form of a concise pretrial motion. State v. 

Herrera, 289 Neb. 575, 856 N.W.2d 310 (2014). It should 

identify, in terms of the Daubert/Schafersman factors, what 

is believed to be lacking with respect to the validity and reliability of the evidence and any challenge to the relevance of 

the evidence to the issues of the case, along with all other 

bases for challenging its admissibility. See id. See, also, State 

v. Ellis, 281 Neb. 571, 799 N.W.2d 267 (2011). The closest 

Simmer’s motion in limine came to raising a challenge to the 

application of TrueAllele in this case was its allegation that 

the proposed testimony was “based on insufficient facts and 

data.” It is far from clear this was specific enough to signal a 

challenge to the application of TrueAllele to the facts of this 

case. See id.

Even assuming Simmer properly preserved the issue, however, we see no basis to find that a conclusion that TrueAllele 

could be reliably applied to the facts of this case would amount 

to an abuse of discretion. To begin, we do not believe the 

Virginia validation study demonstrates that TrueAllele could 

not be reliably applied in this case. Simmer contends a portion 

of that study casts doubt on the conclusions reached in this 

case. One section of that study did, based on testing, conclude 

that TrueAllele produced a “[p]oor” analysis when the standard deviation in the mixture weight was less than .03. And, 

as Simmer points out, Perlin acknowledged that runs of the 
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TrueAllele software yielded a standard deviation below .03 for 

the knife handle.

Perlin did not, however, agree with the Virginia study to the 

extent it concluded that TrueAllele could not produce a reliable analysis when the standard deviation on mixture weights 

fell below a certain threshold. He testified that the Virginia 

study’s results were “a reflection of the data” the authors analyzed and that they inappropriately tried to apply “hard and 

fast thresholds on statistical parameters” rather than “actually looking at concordance in the genotypes in their probability distributions.” Perlin described concordance as similar 

results with acceptably small variations across multiple runs 

of the software. Perlin’s trial testimony also suggests that the 

Virginia laboratory that performed the study eventually came 

to hold his view regarding the reliability of TrueAllele even 

with a low standard deviation in mixture weights: Perlin testified that the laboratory now uses TrueAllele “for all their 

reported mixtures.”

Even setting aside Perlin’s testimony disagreeing with the 

Virginia study’s conclusion as to TrueAllele’s analysis of mixture weights with a standard deviation below .03, the Virginia 

study reached that conclusion in the context of testing performed on three-person mixtures. There is no dispute that 

the sample from the knife handle in this case is a two-person 

mixture. The record does not show that the Virginia study’s 

conclusion regarding standard deviation applies to the facts in 

this case, much less demonstrates that TrueAllele’s analysis 

was unreliable here. Perlin testified that even a 1-percent standard deviation for the two-person mixture on the knife handle 

did not pose a problem for the reliability of the TrueAllele 

results.

Simmer’s argument based on the PCAST report fares no 

better. Simmer contends that this report found that TrueAllele 

was reliable when the minor contributor to a two-person DNA 

mixture contributes at least 10 percent of the mixture. Simmer 

asserts that because the minor contribution on the knife handle 
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in this case was only 2 percent, the PCAST report casts doubt 

on the reliability of the TrueAllele analysis in this case. As we 

will explain, however, the record before us is murky as to what 

the PCAST report concluded, the basis for those conclusions, 

and the weight those conclusions deserve.

The PCAST report is not in our record. Unable to cite 

directly to the report, Simmer directs us to a Washington trial 

court order containing a description of the report. That order 

does note that the report concluded that TrueAllele and a similar software program “appear to be reliable for . . . two person 

mixtures where the minor contributor constitutes at least 10% 

of the mixture.” The same order, however, summarized several 

experts’ criticism of the PCAST report, including its statements 

regarding mixture weights. It also observed that the PCAST 

report did not cite to any study that supported mixture weight 

limitations, a point Perlin also emphasized when he was asked 

about the report on cross-examination. The Washington trial 

court ultimately denied the defendant’s motion to exclude 

TrueAllele evidence despite the fact that the minor contributor 

fell below the limitations purportedly expressed in the PCAST 

report. With no scientific evidence in the record indicating that 

TrueAllele could not generate reliable results under the circumstances here, we cannot say that a conclusion that TrueAllele 

could reliably be applied to the facts of this case would amount 

to an abuse of discretion.

In addition, other evidence in the record did address the 

effect that low mixture weights can have on the TrueAllele 

analysis, but it did not suggest that TrueAllele’s analysis of low 

mixture weights was unreliable. Perlin and the Virginia study 

explained that mixture weights are reflected in the match statistic generated by TrueAllele: the lower the mixture weight, the 

lower the probability given by the match statistic. Therefore, 

the low mixture weight of minor contributor DNA found on 

the knife handle was reflected by the finding that the match 

between the knife handle and Simmer was 3.71 thousand 

times more probable than a coincidental match to an unrelated 
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person, a probability much lower than the match between the 

doorknob and Simmer (4.22 quintillion times more probable 

than a coincidental match to an unrelated person).

The fact that a lower mixture weight makes a match statistic 

less certain is not a basis for exclusion of the evidence. We 

have previously recognized that DNA analysis is not subject 

to exclusion simply because the probability of a match falls 

below a certain threshold. See, State v. Tucker, 301 Neb. 856, 

920 N.W.2d 680 (2018); State v. Ellis, 281 Neb. 571, 799 

N.W.2d 267 (2011). Instead, we have emphasized the need 

for DNA analysis to “be accompanied by evidence of the 

statistical significance of the findings,” and we have rejected 

arguments that jurors are not capable of assigning appropriate weight to those statistics. Tucker, 301 Neb. at 866, 920 

N.W.2d at 688. Here, the evidence furnished the jury with the 

statistical context to carry out its duty. To the extent the disparity between the major and minor contributor on the knife 

handle reduced the certainty of a noncoincidental match, that 

was an issue of weight for the jury to consider and not a bar 

to admissibility.

We see no basis to conclude that the district court could 

not, consistent with our abuse of discretion standard of review, 

conclude that TrueAllele could be reliably applied to the particular facts of this case.

4. Limitations of Our Decision

We conclude by cautioning that this opinion should not be 

understood as mandating the admission of TrueAllele evidence 

in all future cases. “Daubert . . . does not require that courts 

reinvent the wheel each time that evidence is adduced, but it 

does permit the re-examination of certain types of evidence 

where recent developments raise doubts about the validity of 

previously relied-upon theories or techniques.” Schafersman 

v. Agland Coop, 262 Neb. 215, 228, 631 N.W.2d 862, 874 

(2001). And our Daubert framework “permits re-examination 

of the issue if the validity of the prior determination can be 
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appropriately questioned.” Schafersman v. Agland Coop, supra. 

See, also, State v. Casillas, 279 Neb. 820, 782 N.W.2d 882 

(2010). As the instant case demonstrates, “[s]cientific conclusions are subject to perpetual revision” and “hypotheses . . . 

that are incorrect will eventually be shown to be so.” Daubert 

v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579, 597, 113 

S. Ct. 2786, 125 L. Ed. 2d 469 (1993). Based on the record 

before us in this case, however, we cannot say that the district court abused its discretion in allowing admission of the 

TrueAllele evidence.

V. CONCLUSION

For the foregoing reasons, we determine that the district 

court did not abuse its discretion in admitting DNA analysis conducted by using TrueAllele, over Simmer’s Daubert/

Schafersman challenges. Therefore, we affirm.

Affirmed.