Federal Court Says 'Touch DNA' Analysis Is Mostly Guesswork That Can't Be Used As Evidence

from the pyrite-standard-of-evidence dept

DNA was supposed to be the gold standard of criminal evidence. And it can be, but only under very specific circumstances rarely found in the messy world of crime scenes. DNA evidence is easily contaminated by the people handling the evidence, not to mention anyone else who’s been at the crime scene. This has resulted in law enforcement agencies spending years chasing phantom criminals, only to find out the DNA investigators kept finding at crime scenes came from other officers, first responders, or even the person packing their DNA kits back at the manufacturer.

But the myth that DNA evidence is nigh-infallible persists. Some of this is due to the inscrutable nature of the processes that turn stray cells into evidence. Some of this is due to forensic experts overstating the certainty of their findings.

When DNA evidence is pretty much the only evidence holding a case together, the evidence had better be solid. A federal court in Michigan has found that the framework behind one company’s (STRmix) DNA evidence testing is a cobbled-together mess that sounds nice and science-y, but isn’t much more than overly-educated guesswork. (via Grits For Breakfast)

The ruling [PDF] on the defendant’s Daubert motion (a motion that seeks to exclude qualified evidence or testimony) opens with a recounting of the alleged criminal act and the less-than-stellar handling of pretty much the only evidence the prosecution is using to make its case.

Defendant Daniel Gissantaner is charged with a single offense of felon in possession of a firearm, subject to a penalty of not less than 15 years’ and up to life imprisonment; not more than a $250,000 fine; and supervised release of not more than 5 years. The case against Gissantaner rests fundamentally, if not entirely, on a small amount of “touch” DNA taken from a gun in a locked cedar chest during a search of Gissantaner’s house on September 25, 2015, following a dispute with his neighbors over parking in a shared driveway, and police officers’ response to the neighbor’s 911 call. The locked chest containing the gun belonged to Gissantaner’s wife’s daughter’s boyfriend, Cory Patton. Patton, also a convicted felon, had the only key to the locked chest, which was located in Patton’s upstairs bedroom and opened by him at police officers’ request during the search. According to the various police reports, Patton gave conflicting statements about the gun, stating that he heard an argument, went outside, and took the gun away from Gissantaner, but also stating that he never saw Gissantaner with the gun, he found it on the kitchen counter after the argument, and then placed it in the chest.

It seems like the most simple explanation would be that it was Patton’s gun found in Patton’s locked chest that only Patton had a key to. The “conflicting statements” might just have been lies told by Patton because he didn’t want to go away for 15 years minimum. The decision doesn’t say whether Patton’s DNA was ever tested to see if his was present on the gun. All it says is the police handled the evidence sloppily and turned it over to the forensic lab.

The evidentiary handling of the gun is far from pristine. It appears that the gun was moved or handled by at least one police officer before it was taken into evidence. There are also some unexplained delays and unknown whereabouts of the gun between the time it was taken from Gissantaner’s house and the submission to the Michigan State Police (MSP) lab for analysis.

From there, the “touch-DNA” analyst arrived at the conclusion that it was “49 million more times likely” that Gissanter’s DNA was present on the gun, rather than yet another unrelated person’s. The only other contributors to the DNA found on the gun were “two unrelated, unknown contributors.” Even if accurate, this only shows Gissanter had touched the gun. It doesn’t necessarily mean it was Gissanter’s gun.

There are still scientifically-sound methods for DNA testing, like the use of rape kits which already controls for one known DNA sample (the victim’s). “Touch DNA” is almost a pseudoscience. It takes samples that contain a mixture of DNA from surfaces touched by an unknown number of people and makes a guess as to the probability that a criminal suspect’s DNA is among the haystack of unknowns the lab is examining.

When a forensic expert says something is “49 million times more likely,” it seems to indicate something approaching absolute certainty. But that’s not really what this means. Part of the problem with STRmix’s software is that analysts can affect the outcome of tests by manipulating variables.

As Defendant points out, a number of factors entered into the STRMix program are under the control of the operator/analyst or the individual laboratory, and thus are variable, and affect errors. For instance, although “[t]he true number of contributors to a profile is always unknown” (id. at PageID.1075), the individual analyst determines the number of contributors to a DNA profile for purposes of the STRmix™ analysis.


STRMix also relies upon terms set by the individual laboratory, such as analytical thresholds, stutter ratios, drop-in rates, and saturation levels. Furthermore, the input amount of DNA “can have a dramatic impact on the quantity and quality of the STR results obtained,” and “the significance of the likelihood ratios are negatively impacted as the input DNA amount decreases and the extent of allelic and locus drop-out increases.”

The standards and guidelines for “touch DNA” forensics are also a mess. There’s no unified set of standards governing use so analysts are free to create their own baselines. Recommendations from the President’s Council of Advisors on Science and Technology (PCAST) set a baseline for determining “touch DNA” matches but no one’s under any obligation to use them. PCAST’s suggested baseline would have turned the forensic expert’s “49 million times more likely” statement into “results were inconclusive.” That’s a pretty big swing.

[T]he Council stated that “[t]he two most widely-used methods (STRMix and TrueAllele) appear to be reliable within a certain range based on available evidence and the inherent difficulty of the problem”: “Specifically, these methods appear to be reliable for three-person mixtures in which the minor contributor constitutes at least 20 percent of the intact DNA in the mixture and in which the DNA amount exceeds the minimum level required for the method…”

In this case, STRmix “determined” Gissanter only contributed 7% of the DNA analysed, which PCAST said is too low a percentage to be considered reliable.

After more than a year’s worth of expert testimony on the subject of touch DNA testing and STRmix, the court finds this form of DNA testing too unreliable to be considered evidence. The court points to the lack of standardization across law enforcement agencies utilizing the software as well as the lack of objective peer review of research written and published by the developers of STRmix. Throwing a bunch of science together in a blender, like so many DNA samples pulled from a doorknob, is no way to make definitive declarations about probability.

The DNA evidence sought to be admitted in this case—in essence, that it is 49 million times more likely if Daniel Gissantaner is a contributor to the DNA on the gun than if he is not— is not really evidence at all. It is a combination of forensic DNA techniques, mathematical theory, statistical methods (including Monte Carlo-Markov Chain modeling, as in the Monte Carlo gambling venue), decisional theory, computer algorithms, interpretation, and subjective opinions that cannot in the circumstances of this case be said to be a reliable sum of its parts. Our system of justice requires more.

Guesswork is still guesswork, even if it involves technical software and trained analysts. Guesswork is not evidence. Considering what’s at stake, touch DNA analysis isn’t exact enough to meet the evidentiary standard needed to lock people up.

It is the Court’s hope that this decision brings to light the shortcomings or, at the very least, points of inquiry necessary in evaluating this advancing technology as a tool in forensic DNA analysis. There must be a dialogue among key players in the general interest of the development and refinement of the technology, the software and its application by the individuals charged with its use in the field, rather than post-hoc testing of its reliability in the context of a criminal prosecution where the ultimate question is the freedom and guilt or innocence of the person of interest.

The court blocks the admission of this so-called evidence, which means the state really has nothing more than the statements of another convicted felon with a gun in his lockbox to use against the defendant. That’s not going to be nearly enough to secure a possible lifetime imprisonment.

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Comments on “Federal Court Says 'Touch DNA' Analysis Is Mostly Guesswork That Can't Be Used As Evidence”

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This comment has been deemed insightful by the community.
Anonymous Coward says:

The big problem with the statement "49 million times more likely" is that it is an odds ratio. The statement says nothing about the probability the defendant contributed DNA to the gun, merely that he is 49 million times more likely than some unidentified other person. If the chance for the other person is 1-in-200 million, then the chance for Gissantaner might still only be 1-in-4 million even assuming all the theory, calculations, and processing were 100% correct.

Excluding the evidence technically wasn’t really needed since the evidence doesn’t really say anything. But, it is better to exclude it anyway since the prosecution will try to tap-dance around what the statement actually says or simply fail to understand what it actually says and thus prejudice the jury.

This comment has been deemed insightful by the community.
Anonymous Coward says:

Re: Re:

But, it is better to exclude it anyway since the prosecution will try to tap-dance around what the statement actually says or simply fail to understand what it actually says and thus prejudice the jury.

This for sure. Consider two events. The chance of event 1 is 1 in a million. The chance of event 2 is 1 in a billion. Both events are incredibly unlikely. But if you say that event 1 is "1000 times more likely to occur!" – while true, it’s misleading to people (like a jury) who might only have a passing familiarity with probability and statistics: "1000 times more likely? Well that must be what happened!"

Anonymous Coward says:

Re: And yet..

Somehow the gun contained no traces of Patton or the police officers who must have handled the gun? That seems pretty sketchy.

From the Techdirt article:

The decision doesn’t say whether Patton’s DNA was ever tested to see if his was present on the gun. All it says is the police handled the evidence sloppily and turned it over to the forensic lab.

It is not the case that we know that there was no other DNA found on the gun. Rather, it is the case that two unidentified samples were found on the gun, one of which could be the true owner; or those samples could be the result of sloppy handling by the crime scene respondents; or even the result of inaccuracies in the test protocol when faced with low quality inputs.

On the other side, while it seems unlikely given what is stated in the Techdirt piece, it’s possible that the police officers actually wore gloves (or engaged in some other form of isolation/preservation) when handling the weapon, in which case it’s perfectly reasonable that their DNA would not be found.

ECA (profile) says:


In my basic understanding..
DNA has 4 different chemicals in can use in NOT any pattern along the DNA strand..
4*4 gives about 16 points of WHAT 1 point in the strand can be.
But there are many strands that are common for everyone, they dont change much from 1 person to another. And include the Combinations that CANT/Shouldnt happen.
Lets keep it at 4…
How many Locations along the DNA do they test?? 1,2,3-12??
The more you have the closer it can get, and the Messier it gets. At a point its not a 1 day test.
Lets try 6 point 000,000 and each can be 4 different combinations. in basic terms(What Iv heard) that would only be 4,000,000 to 1.. So that in a Nation of 300,000,000 you have a >1% chance? probably 80-90 persons have about or the same combination over 6 points??
ANd then we come to relations, kids esp..Did anyone compare those?? because thats even Closer Avg…
Have fun and 1 time per week, expose the gun to all the kids in the hood..get them all the spit on it, and have LOTS of fun.

Anon says:

Re: Generality..

As I understand it – DNA tests run a chemical process to amplify (reproduce) the DNA found in the sample so they have a lot more to work with. Then they apply certain chemicals which will snip DNA at certain spots (where a particular sequence occurs) into chunks.

Greatly simplified – Apply electrophoresis(?) to determine the length of these chunks. The relative length of certain chunks, in combination(!!) is unique to an individual – they are identified by a string of these numbers. The trouble is with a mixed bag of multiple individuals, the persons could be 1,3,7,4,16,2… and 1,7,4,16,3,8… – or they could be 1,7,7,4… and 1,3,4,16,… – mix and match. Get too many unique individuals in the sample and there are too many combinations. The only definitive thing one could say is if the alleged perp’s unique combination is not possible.

Plus, there’s the issue of free-floating contamination – one sneeze, one stray eyebrow hair, etc. in the sample or the item swabbed… Or even, Joe shakes hands with Bob then handles the gun, Bob’s DNA could now be on it…

This comment has been deemed insightful by the community.
Rekrul says:

TV Detective – We don’t know who the criminal is, so let’s collect all the evidence and meticulously examine it to determine the guilty party’s identity.

Real life detective – I’ve already decided who the criminal is, so look for evidence to prove that I’m right.

bobob says:

Re: Re: Re:

To rule someone out, it’s really only as many locations as it takes to find a difference whether that’s 5 or 20 or whatever, which is the point. The number required to assure a match on the other hand is not well defined and the proceedures of forensics labs have not turned out to be any assurance of scientific integrity, which is why it should be used only to rule people out.

goose62 says:

Touch dna

Im having to go thru this myself right now . me and the wife got into a arguement. And i got bit by her dog so i called police .they let me leave upon leaving i told officers . i have a lot of tools here i want it know there to be safe here and i left ..a hour later the text messaged my wife and told her i told them there was a 22 rifle upstairs .i did not .i had no cell numbers of any officers . she told them it was her gun and she had the only keys to the closet .they told her they didnt believe her .that it was my gun . when i was convicted of a felony i took all my gins to my brothers house and left them . 3 years ago .im 60 years old . my wife is allowed to have a weapon . so when im not here she is safe .now they want me to give my dna to see if its on the gun . im not doing it .so i look for a warrant to be placed this week and me to jail .this is so wrong of a police dept to do to a person .when one is innocent . lost in kansas

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