RECOMMENDED FOR PUBLICATION

Pursuant to Sixth Circuit I.O.P. 32.1(b)

File Name: 21a0057p.06

UNITED STATES COURT OF APPEALS

FOR THE SIXTH CIRCUIT

UNITED STATES OF AMERICA,

Plaintiff-Appellant,

v.

DANIEL GISSANTANER,

Defendant-Appellee.

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No. 19-2305

Appeal from the United States District Court

for the Western District of Michigan at Grand Rapids.

No. 1:17-cr-00130-1—Janet T. Neff, District Judge.

Argued: January 29, 2021

Decided and Filed: March 5, 2021

Before: SUTTON, BUSH, and MURPHY, Circuit Judges.

_________________

COUNSEL

ARGUED: Justin M. Presant, UNITED STATES ATTORNEY’S OFFICE, Grand Rapids, 

Michigan, for Appellant. Joanna C. Kloet, OFFICE OF THE FEDERAL PUBLIC DEFENDER, 

Grand Rapids, Michigan, for Appellee. ON BRIEF: Justin M. Presant, UNITED STATES 

ATTORNEY’S OFFICE, Grand Rapids, Michigan, for Appellant. Joanna C. Kloet, OFFICE OF 

THE FEDERAL PUBLIC DEFENDER, Grand Rapids, Michigan, for Appellee. Maneka Sinha, 

UNIVERSITY OF MARYLAND, Baltimore, Maryland, M. Katherine Philpott, VIRGINIA 

COMMONWEALTH UNIVERSITY, Richmond, Virginia, for Amici Curiae.

>
No. 19-2305 United States v. Gissantaner Page 2

_________________

OPINION

_________________

SUTTON, Circuit Judge. At issue in this case is the reliability of a form of DNA-sorting 

evidence under Rule 702 of the Federal Rules of Evidence and Daubert v. Merrell Dow 

Pharmaceuticals, Inc., 509 U.S. 579 (1993). 

I.

Daniel Gissantaner became embroiled in an argument with his neighbors. One neighbor 

called 911, telling the dispatcher that Gissantaner, a convicted felon, had a gun. The police 

responded to the call and found a pistol inside a chest in Gissantaner’s house. The chest 

belonged to Gissantaner’s roommate. When the government charged Gissantaner with 

possessing a firearm as a felon, it used DNA-sorting evidence, called STRmix, to link 

Gissantaner to the gun.

Gissantaner moved to exclude the evidence as unreliable under Evidence Rule 702. See 

Daubert v. Merrell Dow Pharms., Inc., 509 U.S. 579 (1993). Gissantaner and the government 

retained experts, who took competing positions on the issue. The district court in turn appointed 

two experts of its own to consider the question. One of these experts said that STRmix evidence 

is reliable in general and as applied to this case; the other said it is reliable in general but not as 

applied to this case. The court excluded the STRmix evidence as unreliable. The government 

filed this interlocutory appeal. See 18 U.S.C. § 3731.

II.

DNA evidence has transformed criminal investigations, trials, and post-conviction 

proceedings. Since the late 1980s, it has become a staple of law-enforcement investigations, 

whether to track down the guilty or to liberate the innocent. See Robert J. Norris, Exonerated 35 

(2017). In contrast to blood types and enzymes, an individual’s DNA is unique. United States v. 

Bonds, 12 F.3d 540, 550 (6th Cir. 1993). No one else shares it, save an identical twin. That 
No. 19-2305 United States v. Gissantaner Page 3

makes DNA evidence highly pertinent to the work of forensic scientists tasked with investigating 

crimes. 

Complications arise when a sample of evidence, usually a batch of cells included in fluid 

emitted by an individual or left on an item by touch, contains the DNA of more than one person. 

Consider this case. Police officers collected the relevant evidence on a gun found in a chest 

owned by Gissantaner’s roommate. They collected the “touch DNA”—skin cells found on the 

gun—and submitted it for analysis at Michigan’s statewide law-enforcement laboratory. Based 

on the genetic material in the mixture, an analyst determined that the DNA recovered from the 

weapon came from three people.

In the early years of working with DNA to solve crimes, forensic scientists used one

technique—visual comparison—to handle DNA samples with single and multiple strains. While 

scientists eventually became adept at handling samples with up to two strains of DNA, they 

faced difficulties beyond that. 

A digression into how forensic scientists use DNA evidence helps to explain why. Some 

spots on the human genome, named loci, contain segments of DNA code that vary widely from 

one person to another. Each variation is called an allele, and a person generally has two alleles at 

each locus. Because the alleles vary, no two people are likely to have matching alleles at any 

given locus. A greater number of matching alleles at a greater number of loci increases the 

probability that the person of interest matches the sample. See Special Master’s Report at 17–24,

United States v. Lewis, 442 F. Supp. 3d 1122 (D. Minn. 2020) (No. 18-194). 

One challenge with using mixtures involving several people is that each person might 

have contributed zero, one, or two alleles at each locus. (Although people have two alleles at 

each locus, one or more of the alleles might not have made it into the mixture.) If a mixture 

contains five different alleles at one locus, that could suggest it involves at least three people, 

with two contributors donating two alleles and a third contributor donating one. But other 

possibilities remain. It could be that one contributor gave two alleles and three other contributors 

gave one allele at the locus, suggesting a four-person mixture.
No. 19-2305 United States v. Gissantaner Page 4

Even with these variations, visual examinations of the alleles in a mixture still allow 

examiners to estimate how many DNA sources a touch or fluid sample contains. That is just 

what forensic scientists did in the first decades after they began using DNA to solve crimes.

Visual examinations come with subjective risks, however. The inspection might 

over-count or under-count the percentage of each individual’s contribution to the sample, to the 

extent inspectors calculated the percentage at all, or might mistake the number of people who 

contributed to it. Cf. id. at 21, 23–24. Visual inspection runs the risk of cognitive biases, too. 

Studies suggest that an examiner’s knowledge of the case—other evidence about the

suspect—affects interpretations, frequently not in the suspect’s favor. On top of all that, the 

calculations used to determine the probability of the mixture’s occurring by chance, as opposed 

to coming from the suspect, have to be simplified because human beings, Alan Turing included, 

are not computers.

Enter STRmix and other DNA-sorting products. Starting in the late 1990s, forensic 

scientists innovated products to improve investigations of multi-person DNA samples. The idea 

is to combine the tools of DNA science, statistics, and computer programming to mitigate the 

risks from subjective assessments of multi-person DNA samples. The software in the end helps 

to measure the probability that a mixture of DNA includes a given individual’s DNA. 

In addition to mitigating the risks of human error, the software processes more potential 

interpretations of a mixture in less time. If an analyst remains unsure whether a sample contains 

the DNA of three persons or four, she can use the software to crunch the numbers quickly in both 

ways. The software also mitigates the effect of cognitive bias, as the software does not know the 

other facts of the case. Id. at 23–27. While the software does not eliminate the ever-present 

risks of human error, it “clearly represent[s] a major improvement over purely subjective 

interpretation.” R.41-17 at 93. 

Forensic labs today use several probabilistic genotyping software programs, including 

STRmix, LRmix, Lab Retriever, likeLTD, FST, Armed Xpert, TrueAllele, and DNA View 

Mixture Solution. The product used in this case, STRmix, was created in 2011 by John 
No. 19-2305 United States v. Gissantaner Page 5

Buckleton, a civil servant and forensic scientist who works for the Institute of Environmental 

Science and Research, a government agency in New Zealand.

Roughly 200 forensic science laboratories exist in the United States. Most are affiliated 

with a government. Michigan, for example, has the Michigan State Police laboratory, dedicated 

to providing scientific and technological support to law enforcement throughout the State. Over 

45 of these law-enforcement laboratories use STRmix, with more on the way. R.l39 at 5–6 

(noting that 68 laboratories are in the process of validating STRmix). About ten other 

laboratories use similar products. The FBI uses STRmix. A license for unlimited use of 

STRmix costs about $27,000, with proceeds supporting the work of the New Zealand Institute.

The Biology DNA Unit of the Michigan State Police laboratory has used STRmix for six 

years. The laboratory received training on the software starting in March 2015, and it began 

using the software for cases in February 2016, about three and a half months before receiving the 

sample in this investigation.

In Gissantaner’s case, an analyst with the Michigan State Police laboratory took 

information about the DNA present in the mixture and entered it into STRmix to estimate how 

much of the DNA came from each person. The resulting DNA profile summary said that one 

person “contributed” 68% of the DNA in the mixture, a second contributed 25%, and a third 

contributed 7%. The third contributor supplied 8 or 9 cells (approximately 49 picograms) to the 

mixture.

STRmix compared the DNA of the suspect—Gissantaner—to this profile with the goal of 

ascertaining a “likelihood ratio” about his potential contribution to the sample. R.77 at 34. A 

comparison of Gissantaner’s DNA to the profile suggested that he matched the third contributor, 

generating a likelihood ratio of 49 million to 1. More precisely, if less accessibly, that means the 

DNA “profile is 49 million times more likely if [Gissantaner] is a donor than if he is not.” Id. at 

48.

The two “ifs” capture a qualification. The likelihood ratio tells us only that, in the 

abstract and without considering any other evidence in this case, it would be unusual if this DNA 

contained no DNA contributed from Gissantaner. The ratio does not on its own tell us how 
No. 19-2305 United States v. Gissantaner Page 6

likely it is that Gissantaner illegally possessed a firearm. Determining whether it is likely that 

Gissantaner, as opposed to someone else, contributed to the mixture requires looking at other 

facts beyond the scope of DNA evidence. Perhaps other people with similar profiles, say 

relatives of Gissantaner, were nearby. Perhaps the roommate had locked the chest and lost the 

key long before Gissantaner moved in and had a chance to touch the gun. Or perhaps the DNA 

landed on the gun without Gissantaner touching it, say when he and his roommate shook hands 

or when they each touched the same object before his roommate subsequently touched the gun. 

Even with these qualifications, the evidence remains significant. By accepted measures in the 

forensic community, a profile match of 1 in 49 million amounts to “very strong support” that 

Gissantaner somehow contributed DNA to the mixture. R.41-10 at 3.

These two bottom-line conclusions bring into view the need to use evidence of this sort 

carefully. Such conclusions—the 49-million-to-1 ratio and “very strong support”—can be highly 

probative of guilt or innocence. Yet the mechanisms for obtaining them—the software, the 

science—are beyond the ken of most jurors and judges. If highly consequential evidence 

emerges from what looks like an indecipherable computer program to most non-scientists, 

non-statisticians, and non-programmers, it is imperative that qualified individuals explain how 

the program works and ensure that it produces reliable information about the case. All of this 

explains why the courts have developed reliability standards for admitting evidence of this type 

and why a functioning adversarial system remains critical in handling it. 

III.

Rule 702 of the Federal Rules of Evidence sets the framework for determining whether to 

admit scientific and other technical evidence in federal civil and criminal cases. It permits an 

expert to testify about scientific knowledge if “(a) the expert’s scientific, technical, or other 

specialized knowledge will help the trier of fact to understand the evidence or to determine a fact 

in issue; (b) the testimony is based on sufficient facts or data; (c) the testimony is the product of 

reliable principles and methods; and (d) the expert has reliably applied the principles and 

methods to the facts of the case.” Fed. R. Evid. 702. The same set of questions applies to expert 

testimony and science-based test results. Compare Johnson v. Manitowoc Boom Trucks, Inc., 
No. 19-2305 United States v. Gissantaner Page 7

484 F.3d 426, 427–29 (6th Cir. 2007), with United States v. Semrau, 693 F.3d 510, 516, 520 (6th 

Cir. 2012).

Four inquiries guide the reliability analysis: Is the technique testable? Has it been 

subjected to peer review? What is the error rate and are there standards for lowering it? Is 

the technique generally accepted in the relevant scientific community? Daubert, 509 U.S. at 

593–94. Multi-factor tests, especially non-exhaustive tests, run the risk of obscuring the core 

inquiry. The key handholds of Rule 702 thus bear repeating: To be admissible, any relevant 

scientific or technical evidence must be the “product of reliable principles and methods” and 

must have been “reliably applied” in the case. That is what matters most. Otherwise, the central 

point of Daubert, to establish that Evidence Rule 702 “displaced” the common law Frye test, 

would be lost and would lead to the replacement of an old common law test with a new (harder 

to pronounce) common law test. Compare Frye v. United States, 293 F. 1013, 1014 (D.C. Cir. 

1923), with Daubert, 509 U.S. at 585–89. That is not progress.

Through it all, the district court has a “gatekeeping role” in screening expert testimony to 

ensure that only reliable testimony and evidence go to the jury. Daubert, 509 U.S. at 597. We 

give fresh review to a district court’s framing of the legal standard, United States v. Pugh, 405 

F.3d 390, 397 (6th Cir. 2005), and abuse-of-discretion review to its admissibility decision, 

Kumho Tire Co. v. Carmichael, 526 U.S. 137, 152 (1999). 

IV.

Measured by Evidence Rule 702 and a proper framing of the Daubert factors, the DNA 

evidence should be admitted on this record.

Testability. An untestable scientific theory is all theory and no science. In the absence of 

proof that a technology “can be . . . tested,” Daubert, 509 U.S. at 593, there is no way to show 

whether it works (its “refutability” or “falsifiability,” a scientist would say) and no way to give it 

“scientific status.” Id.; United States v. Bonds, 12 F.3d 540, 559 (6th Cir. 1993). The question 

on the table is whether a method can be “assessed for reliability,” not whether it always gets 

it right. Fed. R. Evid. 702 advisory committee’s note to 2000 amendment; Bonds, 12 F.3d at 

558–59. Disputes about the “adequacy of the [theory’s] testing” or about the “accuracy of 
No. 19-2305 United States v. Gissantaner Page 8

[a theory’s] results,” generally speaking, provide grist for adversarial examination, not grounds 

for exclusion. Bonds, 12 F.3d at 558–59; see United States v. Mitchell, 365 F.3d 215, 238 (3d 

Cir. 2004); see also City of Pomona v. SQM N. Am. Corp., 750 F.3d 1036, 1046 (9th Cir. 2014); 

United States v. Baines, 573 F.3d 979, 989–90 (10th Cir. 2009).

STRmix can be tested. Using “lab-created mixtures,” in which the actual contributors of 

the DNA samples are known, scientists have tested STRmix to gauge the reliability of the 

technology. R.146-14 at 2. Suppose that one person, Aaron, contributed to a lab-created 

mixture, but another, Britney, did not. Forensic scientists can test STRmix to see whether it 

suggests that Aaron is a match for the mixture, but Britney is not. If STRmix suggests that 

Aaron is not a match for the mixture (by outputting a low likelihood ratio), that would be a false 

negative. If STRmix suggests that Britney is a match for the mixture (by outputting a high 

likelihood ratio), that would be a false positive. Each possibility shows that STRmix is testable, 

that lab-created mixtures offer a way to “assess[] [the] reliability” of STRmix. Fed. R. Evid. 702 

advisory committee’s note to 2000 amendment. 

The record from the evidentiary hearings in this case provides a long proof that STRmix 

is testable and refutable. Almost all of the evidence in the hearings went to these points: How 

often is it accurate? How often is it not? Similar evidence of DNA testability has sufficed 

before in our circuit. Bonds, 12 F.3d at 558.

(The astute reader might remind us that Daubert asks whether the scientific theory at 

issue “can be (and has been) tested.” 509 U.S. at 593. It is not clear what the parenthetical 

means. The rest of the Daubert considerations—including the next one, peer review—all turn in 

one way or another on what actual testing of the theory reveals in terms of reliability. At all 

events, the point makes no difference here. STRmix indeed “(has been) tested” many times 

before, as the rest of this opinion confirms.)

Peer review. Subjecting a new technology to “peer review and publication” offers 

another measure of reliability. Id. The “key” is whether “the theory and procedures have been 

submitted to the scrutiny of the scientific community.” Bonds, 12 F.3d at 559. Publication in a 

peer-reviewed journal typically satisfies this consideration. See Daubert, 509 U.S. at 594. 
No. 19-2305 United States v. Gissantaner Page 9

Peer review is not student review. It “conditions publication on a bona fide process” of 

review by other scientists and experts in the field. Daubert v. Merrell Dow Pharms., Inc., 

43 F.3d 1311, 1318 n.6 (9th Cir. 1995). The scientific community uses different conventions for 

publication from most journals published in the legal community. No offense to former, current, 

and future members of law journals everywhere: But it is one thing to convince lawyers in

training to publish a piece; it is quite another to convince peers in a professional community to 

publish a piece. That is why readership and citation are pivotal when it comes to legal 

scholarship and why publication itself is noteworthy in scientific scholarship—and ultimately 

why publication in a peer-reviewed journal alone typically satisfies this Daubert inquiry. See 

Ruiz-Troche v. Pepsi Cola of P.R. Bottling Co., 161 F.3d 77, 84–85 (1st Cir. 1998); In re Paoli 

R.R. Yard PCB Litig., 35 F.3d 717, 781 (3d Cir. 1994); United States v. Brown, 973 F.3d 667, 

704 (7th Cir. 2020); cf. Allison v. McGhan Med. Corp., 184 F.3d 1300, 1316 (11th Cir. 1999); 

Summit 6, LLC v. Samsung Elecs. Co., 802 F.3d 1283, 1295 (Fed. Cir. 2015). 

For like reasons, this factor does not demand independent authorship—studies done by 

individuals unaffiliated with the developers of the technology. Independent studies, to be sure, 

advance the cause of reliability. Bonds, 12 F.3d at 560. But they are not indispensable. Peer 

review contains its own independence, as it involves “anonymously reviewing a given 

experimenter’s methods, data, and conclusions on paper.” Mitchell, 365 F.3d at 238. If experts 

“have other scientists review their work” and if the other scientists have the chance to identify 

any methodological flaws, that usually suffices. Mitchell v. Gencorp Inc., 165 F.3d 778, 784 

(10th Cir. 1999). When scientific research is accepted for publication by a reputable journal 

following the “usual rigors of peer review,” that represents “a significant indication that it is 

taken seriously by other scientists, i.e., that it meets at least the minimal criteria of good 

science.” Daubert, 43 F.3d at 1318. 

STRmix clears this bar. At the time of the Daubert hearing in the district court, more 

than 50 published peer-reviewed articles had addressed STRmix. According to one expert, 

STRmix is the “most tested and most . . . peer reviewed” probabilistic genotyping software 

available. R.77 at 82. At least two of the studies were done by individuals unconnected to the 
No. 19-2305 United States v. Gissantaner Page 10

development of the software. This plainly suffices. Bonds, 12 F.3d at 559–60; cf. Gross v. 

Comm’r, 272 F.3d 333, 340–41 (6th Cir. 2001).

Error rate and standards to lower it. Even ten witnesses to a crime come with risks of 

error. So too for DNA evidence. This consideration looks to the error rate of the technology and 

to whether the scientific community has established standards that forensic scientists can use to 

mitigate the risk of error. Daubert, 509 U.S. at 594.

Think about Gissantaner’s case to see the point. The government would like to use 

STRmix to match Gissantaner to the DNA on a gun. That is not a good idea—not the “product 

of reliable principles and methods” under Rule 702—if STRmix has a high error rate, if it has 

trouble “avoid[ing]” “false positives,” and if there are no standards or guidelines to avoid or

lessen these risks. Bonds, 12 F.3d at 559 (quotation omitted); Mitchell, 365 F.3d at 241. 

How often, then, does STRmix falsely suggest a suspect matches a DNA sample? Not 

often, the evidence suggests. When examining “false inclusions,” one peer-reviewed study 

concluded, based on an analysis of the DNA of 300,000 people who were known not to be in a 

mixture, that STRmix had accurately excluded the non-contributors 99.1% of the time. Just 1% 

of the time, in other words, it gave a likelihood ratio suggesting that someone was included in the 

mixture who was not actually included in it. Most of these false inclusions, moreover, were 

associated with low likelihood ratios—meaning that, under STRmix’s own estimates, the 

confidence that the person was included was low. A likelihood ratio of 100 to 1 is more likely to 

produce a false inclusion than a likelihood ratio of 1 million to 1. In this instance, the likelihood 

ratio was 49 million to 1.

One explanation for the low error rate is the existence of standards to guide the use of 

STRmix and other probabilistic genotyping software, for the two are “[c]losely related.” 

Mitchell, 365 F.3d at 241. The Scientific Working Group on DNA Analysis Methods, a national 

association of forensic laboratories sponsored by the FBI, has produced guidelines governing the 

use of this kind of software, guidelines that the Michigan State Police laboratory used in this 

case.
No. 19-2305 United States v. Gissantaner Page 11

General acceptance in the scientific community. One might still be skeptical of the 

reliability of a relatively new technology like STRmix, and rightly so, if the relevant scientific 

community has not yet accepted its use. Daubert, 509 U.S. at 594. The question for debate is 

“general acceptance,” not uniform acceptance within the community. See Bonds, 12 F.3d at 562. 

Nor must the science be beyond reproach. Id. What matters is whether the relevant scientific 

community accepts the software. See Daubert, 509 U.S. at 594; see also Wilden v. Laury 

Transp., LLC, 901 F.3d 644, 654–55 (6th Cir. 2018). After that, the long-tested cauldron of 

cross-examination, not exclusion, is the place to go for accuracy. “[C]onventional [trial] devices, 

rather than wholesale exclusion under an uncompromising ‘general acceptance’ test, are the 

appropriate safeguards where the basis of scientific testimony meets the standards of Rule 702.” 

Daubert, 509 U.S. at 596. For a technology that is widely used, controversies over its use in a 

given case usually will be left to the jury. See United States v. Jones, 965 F.3d 149, 160 (2d Cir. 

2020). 

STRmix satisfies this consideration. It has garnered wide use in forensic laboratories 

across the country. More than 45 laboratories use it, including the FBI and many state law 

enforcement agencies. At this point, STRmix is the “market leader in probabilistic genotyping 

software.” R.146-1 at 17.

Consistent with this reality, numerous courts have admitted STRmix over challenges to 

its general acceptance in the relevant scientific community. See United States v. Lewis, 442 F. 

Supp. 3d 1122, 1155 (D. Minn. 2020) (“[T]here is no doubt that STRmix has gained general 

acceptance.”); United States v. Washington, No. 8:19CR299, 2020 WL 3265142, at *2 (D. Neb. 

June 16, 2020) (“Authority and evidence demonstrate that STRmix is generally accepted by the 

relevant community.”); People v. Blash, No. ST-2015-CR-0000156, 2018 WL 4062322, at *6 

(V.I. Super. Ct. Aug. 24, 2018); People v. Muhammad, 931 N.W.2d 20, 30 (Mich. Ct. App. 

2018); People v. Bullard-Daniel, 42 N.Y.S.3d 714, 724–25 (N.Y. Co. Ct. 2016); United States v. 

Christensen, No. 17-CR-20037-JES-JEH, 2019 WL 651500, at *2 (C.D. Ill. Feb. 15, 2019) 

(“STRmix has been repeatedly tested and widely accepted by the scientific community.”); 

United States v. Oldman, No.18-CR-0020-SWS, ECF No. 227 at *16 & n.5 (D. Wyo. Dec. 31, 

2018) (collecting cases); United States v. Russell, No. CR-14-2563 MCA, 2018 WL 7286831, at 
No. 19-2305 United States v. Gissantaner Page 12

*7–8 (D.N.M. Jan. 10, 2018) (“[STRmix’s] analyses are based on calculations recognized as 

reliable in the field.”); United States v. Pettway, No. 12-CR-103S (1), (2), 2016 WL 6134493, at 

*1 (W.D.N.Y. Oct. 21, 2016) (discussing “exhaustive[] research[]” concluding that “the 

scientific foundations of the STRmix process are based on principles widely accepted in the 

scientific and forensic science communities”). The Second Circuit determined that the scientific 

community accepted a different (but similar) DNA-sorting software, Forensic Statistical Tool, 

even though just one laboratory had used it. Jones, 965 F.3d at 156, 162.

General acceptance of probabilistic genotyping software, moreover, has led to its 

use in inculpatory and exculpatory settings alike. See Erik Ortiz, A Texas 

jury found him guilty of murder. A computer algorithm proved his innocence., 

https://news.yahoo.com/prison-murder-computer-algorithm-helped-105609137.html (last visited

March 3, 2021); Jason Hanna & Nick Valencia, Thanks to a new DNA analysis, a Georgia man 

is exonerated of rape and freed from prison after 17 years, 

https://www.cnn.com/2020/01/10/us/georgia-kerry-robinson-released/index.html (last visited 

March 3, 2021). 

All in all, STRmix satisfies Rule 702 and the case law construing it. In the words of Rule 

702, it is the “product of reliable principles and methods.”

V.

But were those principles “reliably applied” in this case, as Rule 702 also asks? Yes, as 

we explain and as the record in this case demonstrates. 

The Michigan State Police laboratory complies with the guidelines promulgated by the 

Scientific Working Group, as confirmed through an audit performed by the FBI. The forensic 

scientist who ran the sample in this case began training with STRmix more than a year before 

analyzing the sample. During that time, the laboratory tested its copy of the software, using 

lab-created mixtures to establish “internal validation” that STRmix reliably assisted the 

laboratory’s work. R.77 at 52. In addition to these artificial mixtures, the laboratory tested 

adjudicated-case samples, real samples from real crime scenes. It produced a summary 

explaining the results of its tests and offered additional data to supplement the summary. In 
No. 19-2305 United States v. Gissantaner Page 13

general, the laboratory’s use of STRmix produced “significant likelihood ratios” for known 

contributors and improbable ones for known non-contributors. R.41-14 at 43. 

The Michigan State Police laboratory’s internal validation also included samples like the 

one in this case in which a minor contributor donated a small amount of DNA. It tested a 

mixture in which one contributor gave just 4% of the DNA (less than the 7% here) and another 

mixture in which the minor contributor gave only 26 picograms of DNA (less than the 49 

picograms here). The laboratory also produced supplemental data showing that its internal 

validation included a lab-created mixture of 3.2% and 32 picograms and an adjudicated-case 

mixture of 4% and 10 picograms. The government offered to provide still more data for those 

interested, but the district court declined the offer. 

STRmix also accounts for small amounts of DNA when it creates profile summaries. 

Because less DNA in a sample creates more uncertainty, STRmix generates lower likelihood 

ratios for low-quantity DNA mixtures than it otherwise would. The software also errs in the 

direction of the innocence of criminal suspects by making conservative estimates about the 

probability of a genetic pattern occurring.

The Michigan State Police laboratory has ample company in concluding that STRmix 

works at low levels of DNA. A peer-reviewed article compiling data from the internal 

validations of 31 independent laboratories indicated that STRmix had been validated with 

mixtures involving a minor contributor who supplied a small percentage of a mixture. The FBI’s 

internal validation, also subjected to peer review, included mixtures in which the minor 

contributor contributed less than 7% and fewer than 49 picograms to the sample. Gissantaner did 

not introduce any studies showing STRmix is unreliable at low levels. 

On this record, the “reliable principles and methods” underpinning STRmix were 

“reliably applied” in this case. Fed. R. Evid. 702. Any lingering concerns about how the 

Michigan State Police laboratory presented the information from its internal validation study or 

doubts about the reliability of STRmix at low levels of DNA can be hashed out through 

cross-examination or testing by the defendant. On appeal, Gissantaner and his team have not 

objected to the level of access the owners have provided to the program’s source code or to their 
No. 19-2305 United States v. Gissantaner Page 14

ability to run their own tests at different parameters as well as to observe how the laboratory 

operates STRmix. While they have not used their access to this information yet to undermine the 

reliability of STRmix in general, they remain free to do so at trial.

VI.

Gissantaner resists this conclusion on several fronts, each unconvincing.

He claims that the standard of review favors him. That is true. But a district court may 

abuse its discretion by incorrectly framing the legal standard. See United States v. Flowers, 963 

F.3d 492, 497 (6th Cir. 2020); Pugh, 405 F.3d at 397. The meaning of Evidence Rule 702, and 

for that matter the Daubert considerations, amounts to a legal question. See United States v. 

Jones, 107 F.3d 1147, 1154 (6th Cir. 1997); Bureau v. State Farm Fire & Cas. Co., 129 F. 

App’x 972, 975 (6th Cir. 2005).

The district court framed several Daubert factors incorrectly. Start with testability. The 

district court pitched the question as “whether the use of STRmix has been adequately tested and 

validated, independently of the testing by the developer.” R.161 at 30. It then identified 

“shortcomings,” id. at 31, in the way that the Michigan State Police laboratory had displayed its 

test results, leading the court to conclude that the factor weighed “strongly against” admitting 

STRmix, id. at 35. Even “serious deficiencies” in testing, however, do not render a method 

untestable. Bonds, 12 F.3d at 559. At stake is “scientific validity,” not “scientific precision.” Id.

at 558. Gissantaner’s, and the district court’s, “attempt[s] to refute the [government’s] theory 

and methods with evidence about deficiencies in both the results and the testing of the results,” 

amounts to a “conce[ssion] that the theory and methods can be tested.” Id. at 559. Although the 

independent experts in this case disagreed about the adequacy of the testing, that does not mean 

the theory is untestable or even that it has not been tested. Id.

Move to peer review. The district court’s position—that the factor requires studies 

authored or conducted independently of the developers of STRmix—misapprehends the inquiry. 

Independent authorship may (or may not) represent the scientific ideal, but submission to peer 

review generally suffices under Daubert. The court also overstated the risks of allowing the 

developers of a new technology to be the ones who test it. The key developer of STRmix is a 
No. 19-2305 United States v. Gissantaner Page 15

civil servant who works for New Zealand. Any revenue from sales of the software goes to a 

government agency, which by all appearances seems as focused on sparing the innocent as on 

convicting the guilty. What inculpates one day may exonerate the next with DNA-sorting 

evidence.

But even if that were not the case, even if STRmix had been developed by a for-profit 

entity, that would not belittle its reliability. Think of all the medical and scientific breakthroughs 

innovated by private corporations. Once one starts compiling that list, it is hard to stop. Come 

to think of it, how many of the vaccines for COVID-19 grew out of not-for-profit work? Peer 

review, together with the other Daubert factors, works well in handling the self-interest, whether 

modest or extravagant, that comes with any invention.

Close with general acceptance. In concluding that this “factor does not add weight for a 

finding that the STRmix DNA analysis is reliable,” R.161 at 43, the district court rooted its 

reasoning in the concern that STRmix “remains controversial” among a subset of the scientific 

community (computer scientists) and in cases involving small amounts of DNA. Id. But the 

existence of criticism, particularly as applied in specific cases, does not mean that STRmix has 

fallen short of “general” acceptance. The criticism at all events is overstated. Recall that the 

court appointed two experts under Evidence Rule 706. It then claimed that, because these two 

independent experts disagreed about using STRmix in this case, that meant it failed Daubert. 

But one of the experts, Dr. Krane, was not as independent as the court suggested. He was the 

president of the firm that employed Gissantaner’s expert, and he had previously worked on the 

case for Gissantaner, all points explained to the court by the government. That does not prohibit 

Dr. Krane from offering expert testimony about STRmix on behalf of Gissantaner. It just means 

he should not have been treated as an independent Rule 706 expert in the case. See 29 Charles 

Alan Wright & Victor Gold, Federal Practice and Procedure § 6304 (2d ed. 2016); cf. Gates v. 

United States, 707 F.2d 1141, 1144 (10th Cir. 1983) (per curiam). All told, there was no conflict 

between independent experts about the generally reliability of STRmix at low percentages and 

low weights. In truth, the only independent expert in the case found it reliable.

The district court’s misframing of these three factors provides one ground for our 

decision. Another is that the complete exclusion of such widely used scientific evidence, at least 
No. 19-2305 United States v. Gissantaner Page 16

on this record, would amount to an abuse of discretion anyway. The district court mainly 

questioned the reliability of this evidence because the Michigan State Police laboratory did not 

internally validate STRmix at low contribution and weight levels. As shown, however, the 

laboratory did validate STRmix at these levels, and so did the FBI. The district court’s concerns 

with the laboratory’s internal validation stemmed largely from the way the data was presented: 

(1) The validation summary did not mention mixtures similar to the one here—in which the 

minor contributor donated a small absolute amount of DNA (49 picograms) and a small 

percentage of the DNA in the mixture (7%)—and (2) the supplemental data, which explained 

that the Michigan State Police laboratory ran tests on similar mixtures, did not include the 

likelihood ratios or the false-positive rates from those tests. 

Rule 702 does not require unstinting perfection in presenting test results. In light of the 

extensive evidence of STRmix reliability, including at low levels, these concerns were for the 

jury, not the court. See Kumho Tire, 526 U.S. at 153 (explaining that if reasonable experts 

disagree, that is usually for the jury, not the court). If the district court still wished to exclude the 

evidence based on a lack of data from the Michigan State Police laboratory’s internal validation, 

it should have taken up the government’s offer to present more evidence from the internal 

validation study. That is especially so given that the government had so far made good in 

responding to shifting requests from Dr. Krane throughout the case. Maybe the government has 

the precise false-positive rates from the laboratory’s internal study; maybe it does not. If it does, 

its failure to anticipate the independent expert’s exact request does not justify excluding 

STRmix. If it does not, any missing pieces can be used on cross-examination. 

The court’s reasoning in excluding the evidence gives pause in another respect. The key 

concern expressed by the court was the low percentage and low quantity (just 8 or 9 cells) 

supplied by the minor contributor. But it is the STRmix software, and nothing else, that supplied 

the factual premise for these points. It is puzzling to think that STRmix would be sufficiently 

reliable to show that the minor contributor gave just 7% of the sample but then to cast doubt on 

7% samples in general and to do so when combined with low weight samples (49 picograms) in 

particular. Neither the district court nor Dr. Krane acknowledges, much less explains, the point.
No. 19-2305 United States v. Gissantaner Page 17

As this last point suggests, the admissibility of this evidence is not the end of the road for 

Gissantaner. It may help him in some ways. Recall what the low 7% figure—created thanks to 

STRmix—means. It suggests that Gissantaner contributed only 8 or 9 cells to the mixture of 

DNA found on the gun. Holding a gun may not be the only way in which a small number of 

cells could land on a gun. Gissantaner was the roommate of the gun’s owner. Perhaps their 

interaction, their shared use of objects in the kitchen, or their shared touching of objects in the 

house affected the sample. That is what trials and juries are for. Both sides also will have ample 

opportunities to show whether the Michigan State Police laboratory’s testing of this sample was 

handled correctly and used correctly, and Gissantaner remains free to identify defects in the 

STRmix software. We have not hesitated to correct civil or criminal verdicts in which the trial 

record showed that the science was misused. See Tamraz v. Lincoln Elec. Co., 620 F.3d 665 (6th 

Cir. 2010). Evidence Rule 403 also remains relevant to the inquiry. A district court concerned 

that the jury might misunderstand what the likelihood ratio means could require advocates to 

describe it in a way that will not generate “unfair prejudice” or “mislead[] the jury.” Fed. R. 

Evid. 403. Even with the admission of STRmix, the government still must show “beyond a 

reasonable doubt” that Gissantaner possessed the gun. See Jackson v. Virginia, 443 U.S. 307, 

309 (1979). That may become a critical question if no other credible evidence shows that 

Gissantaner handled this gun.

We reverse.