United States v. Gissantaner

Decision Date05 March 2021
Docket NumberNo. 19-2305,19-2305
Citation990 F.3d 457
Parties UNITED STATES of America, Plaintiff-Appellant, v. Daniel GISSANTANER, Defendant-Appellee.
CourtU.S. Court of Appeals — Sixth Circuit

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.

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

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


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, 113 S.Ct. 2786, 125 L.Ed.2d 469 (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.


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 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).

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.

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 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 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...

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