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FBI Fights Testing For False DNA Matches
Statesman writes "The Los Angeles Times reports that an Arizona crime lab technician found two felons with remarkably similar genetic profiles, so similar that they would ordinarily be accepted in court as a match, but one felon was black and the other white. The FBI estimated the odds of unrelated people sharing those genetic markers to be as remote as 1 in 113 billion. Dozens of similar matches have been found, and these findings raise questions about the accuracy of the FBI's DNA statistics. Scientists and legal experts want to test the accuracy of official statistics using the nearly 6 million profiles in CODIS, the national system that includes most state and local databases. The FBI has tried to block distribution of the Arizona results and is blocking people from performing similar searches using CODIS. A legal fight is brewing over whether the nation's genetic databases ought to be opened to wider scrutiny. At stake is the credibility of the odds often cited in DNA cases, which can suggest an all but certain link between a suspect and a crime scene."
Unless the crime labs start encoding the full DNA sequence, even then identical twins will duplicate, the best DNA, for that matter finger prints, can do is prove it is *NOT* that person.
It is hard to believe the FBI won't do the study to get real numbers, but we've been here before. These are the same people who presented bullet lead evidence with equal certainty. The science is impressive but it means nothing when your original premise is wrong. In the bullet lead case, it turns out that matches were common and single boxes often had differences. The coincidence between two people is good reason to review the data and make sure DNA statistics are correct. Until that is done, the odds of DNA matches should be looked on with great skepticism.
It's screw ups like this that make the death penalty a bad idea. While life in prison is a terrible punishment, perhaps more cruel than death, it gives the state a chance to fix its mistakes.
DMCA, Hollings, Palladium. What might have sounded like paranoia is now common sense.
Just thinking out loud here, but is it actually wrong?
Even though the odds of sharing a birthday with a random person are about 1/365, if you have 23 people in a room, you are likely to have at least one "birthday" match. With about 60 people, it's almost a certainty.
A back-of-the-envelope calculation gives me about half a million as the number of DNA samples required to give a 50/50 chance of having two people with matching DNA samples... but I might have messed up on that.
There has never yet been a 13-locus match seen between unrelated people in the national database- despite the 5 million or so profiles currently in it. I'm sure the average Slashdot reader can manage to work out how many pairwise comparisons that is. (Hint- it's a pretty fucking big number.)
Well it seems that your statement of 'never' is simply because that comparison has not been run, since the FBI is doing everything possible to prevent testing of that theory. If its so unimaginably rare, it would seem that the FBI would be all for doing these searches to bolster the value of their evidence. However the results in MD would seem to challenge that dogma.
A 9-locus match between unrelated people is not surprising. That's why we don't sue only 9 loci, idiots!
Well it seems that California prosecutors are idiots and were using a 9 locus match to prosecute a man for a 2 decade old murder. From TFA: "Its implications became clear as she prepared to defend a client accused of a 20-year-old rape and murder. A database search had found a nine-locus match between his DNA profile and semen found in the victim's body. Based on FBI estimates, the prosecutor said the odds of a coincidental match were as remote as 1 in 108 trillion." So just to explain why we 'idiots' would use a 9 locus match: DNA collected at a crime scene is not a complete genome. Often it is only fragments. You may not have a full 13 loci to check because the fragment you have would not cover all 13 loci. There is, however a statistical nicety here that you've completely side-stepped in your haste to call us morons (which TFA mentions). The likelihood of finding matches of 9 of the 9 you have in your genome fragment is far less than the likelihood of finding any two people in a database with 9 of any 9 of 13 loci that match.
From the description, this seems like an example of the birthday problem. Briefly, in a group of 23 people the odds are 50-50 that two of them will have the same birthday, while in a group of 57 the odds are better than 99%. However, the odds that someone in the first group will share *your* birthday are far less, roughly 6.1%. Quoting the Wikipedia article, "For a greater than 50% chance that one person in a roomful of n people has the same birthday as you, n would need to be at least 253. Note that this number is significantly higher than 365/2 = 182.5: the reason is that it is likely that there are some birthday matches among the other people in the room."
Likewise, the odds of there being two people with matching DNA in a database are far higher than the odds of someone else matching *your* DNA. So it seems possible that the FBI could be quoting accurate odds, while at the same time there being lots of matches within the database.
Nothing for 6-digit uids?
The other question is: since the database was started, our ability to study DNA, examine genetic markers and recognize which areas are better for identifying individuals has drastically improved. Has the database improved to match this knowledge, or are we relying on outmoded methods? If the former, then it's as good as it is going to get - for now. If the latter, the probability of a false positive could be massively slashed. That would surely be desirable for a crime-fighting system... wouldn't it?
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
So what you are saying is that a new sample has a 1 in 19,000 chance (6e6/1.13e11) of finding a match in CODIS at random, even though this is a new sample not present in the database. With thousands of police departments nationwide running samples against CODIS every week, false matches like this may occur frequently. If the consequence is that an innocent person is charged or even convicted of rape or murder, this is frightening.
There is a big difference between telling a lay jury "this match had a one in a 113 billion chance of occurring at random" versus "this is an event that occurs randomly on a routine basis." Non-statisticians have a hard time getting their head around the concept of correction for multiple hypothesis testing.
The real problem is that the FBI match criteria were developed years ago when the CODIS database was small compared to its current size, and these criteria have not been updated in light of growth in the database and new technology. Using state-of-the-art genotyping technology, it should be possible to design a test with a small chance of a false positive match even if the database contained the entire US population.
Statesman
Just wait until they start outsourcing prisons to China. Won't that be all kinds of fun?
God, I wish I were joking.
God invented whiskey so the Irish would not rule the world.
There's a difference. A prosecutor in the situation you give is placing his own career interests above the interests of justice and the law.
A defense lawyer getting someone off "on a technicality" is at the very least demonstrating an allegiance to the letter of the law and a commitment to see that all people are treated under the law equally... and often may be the last line of defense against a government bent on violating civil rights.
There's really no such thing as "getting off on a technicality." Whenever you hear that phrase it's coming from a prosecutor or police officer who at the least didn't do their job properly and at worst violated the law themselves, and got caught.
When the police searched you illegally, you "got off on a technicality."
When they came into your home without a warrant, you "got off on a technicality."
When they didn't properly document and control the chain of possession of evidence used to convict you, thus throwing into doubt whether it's even legitimate evidence, you "got off on a technicality."
When they interrogated you improperly or otherwise throw into question the accuracy of what they claim is your testimony to police, you "got off on a technicality."
When they selectively show your photo to or otherwise lead the victim into presupposing you are the guy who did it, you "got off on a technicality."
When the prosecutor has withheld information that might have exonerated you or changed a jury's verdict, you "got off on a technicality."
"Got off on a technicality" = not guilty.
This space available.
I've noticed something: government conspiracies always get modded up here and are usually based on "Think about it. You know it's true, man."
The reason overly pessimistic posts about the government get modded up and not overly optimistic ones seems to be that your average slashdotter is insecure and doesn't want to get lauged at for being naive.
Well call me naive, but I don't think things like this are driven by greed so much as incompetence, hubris, and an "us vs them" mindset.
"If they truly cared about justice they'd say "hey we need to take another look at this". I don't know how they can live with that on their conscience anymore than I understand how defense lawyers can live with setting rapists and killers free on technicalities."
There's a difference. A prosecutor in the situation you give is placing his own career interests above the interests of justice and the law.
No, no, no. Three words explain why the prosecutor doesn't want to re-try the case and why this is the right thing to do in the circumstances: adversarial justice system.
It may not be the best system, but it's what we have; it is the duty of the prosecution to assume that they are right, just as it is the duty of the defence to assume that the prosecution is wrong. To allow the prosecutor to pick and choose the circumstances in which to present a strong case vs the circumstances in which to side with the defence introduces more bias into the system. Each side must present their case as if it was absolutely the way that they say it is, and then the jury must weigh the circumstances and decide.
I do know where you're coming from, and I'd certainly hate to be considered a conspiracy nut. I do try to liberally apply the idiom "never attribute to malice what can be adequately explained by incompetence".
All that said, however, I'm not really seeing a reason here that can be explained by simple incompetence. If they are, at heart, good people, then they would want to know how accurate DNA results are. It wouldn't even expose them to looking bad if it turned out that they'd been using bad evidence - all they'd need to save face would be a photo of an FBI agent shaking hands with someone in a lab coat and a press release explaining how grateful they are for having this weakness in the testing system found. Any other ideas on why they'd want this not to be looked into?
I think the answer is that most lawyers in general lack a conscience, you'd have to to be successful.
Disclaimer: my bar exam is a week from Tuesday.
I've had this conversation with people before, its why I want to stay out of criminal work. I guess the theory is that you throw everything on the table and hope that the opposing attorney is doing their job. That's the adversarial system. The Constitution dictates that the prosecution has to throw a lot more on the table. Ethics rules dictate that the prosecution also has to defeat their own case when they have information that will damage it. The defense attorney just has to do the best he can with the facts he is given.
Its easy to malign both sides of the system. However, neither is an easy task. The prosecution is ethically responsible for both society's interest, and to some extant, the defendant's as well. The defense attorney is responsible for the defendant's interest but, to a broader extent, society's interests as well. Defense attorneys protect even you and me in the sense that those accused of crimes, whether innocent or guilty, set the periphery of our legal protections. Guilty people have been responsible for the liberties you and I enjoy because they challenged the procedure, actions, and level of proof employed by the government. Whether or not an attorney is scum or devoid of conscience, there is an attorney on the other side taking them to task. Sure its an imperfect system, but its the best society can come up with and we muddle through.
Why have 1 person driving a backhoe when you could employ 20 with shovels?
Any other ideas on why they'd want this not to be looked into?
It's human nature not to want to admit mistakes, even to yourself. These people have spent years convicting people on DNA, and in the mind of the public it's rock solid -- if they have you on DNA, case closed.
The upheaval in the court system will be huge. All cases where DNA evidence was used will have to be retried. Throw in the mentality of "we know he's guilty anyways" based on other evidence, and it's not surprising that the FBI would rather sweep this under the carpet.
The idea that the FBI is part of some conspiracy to get slave labor is absurd.