On the Dangers and Potential Abuses of DNA Familial Searching

Advocatus Diaboli sends a story of how a high tech forensic procedure almost led investigators to the wrong person. In 1996, a young woman named Angie Dodge was assaulted and murdered in Idaho Falls, Idaho. There was a conviction in the case, but later reports claimed the wrong man was in prison, and police thought there were more than one attacker anyway. This eventually led to the re-opening of the investigation. Using DNA evidence that had been preserved from the crime scene, police used a controversial technique called familial searching to try to find a lead. This method is used when there is no direct DNA match within the available databases. Instead, it tries to identify family members of the suspect. Police found a partial match, which eventually led them to Michael Usry, a New Orleans filmmaker. They convinced a judge to provide a search warrant to extract Usry's DNA and test it against the sample. It wasn't until a month after the extraction that they told him he'd been cleared.

Comments

System worked, then?

[CrimsonAvenger]

So, they got a warrant like they're supposed to.

Then they executed the warrant, gathered a DNA sample, and tested it.

Sample came back as not matching, so they removed the suspect from their list of suspects.

So, what's the problem here? They checked out a lead (using legal methods, like a warrant), found it went nowhere, and continued the investigation into other possible leads....

Re:System worked, then?

[DarkOx]

I think the problem here, if there is one (and I am with you on not being so sure there is) just how far removed from an event under investigation do you need to before you can't be subject to warrants related to it.

Right now a Judge or Magistrate basically determines this. I am not sure what standards may exist beyond probably cause of finding evidence. So here we have a guy where there is nothing at all to tie him to the events except DNA match that is actually exculpatory in that its clear he isn't a match for the sample the Police believe is that of the perps; however it does indicate he may be a family member however distant. The police want to confirm this. Is it reasonable to "search" his blood to confirm the match, and is that than cause to search everyone one of his relations, and their offspring?

Its kinda like the NSA's 3 degrees thing, does this simply open the door to the government being free to collect DNA samples form most citizens? We do need to look at some old assumptions in the face of new tech. In the past you had to manually do DNA compares between two samples, now you digitize results and search a database. Where you would not in the past have do a comparison with someone who could not have committed the crime now you effective compare with every sample taken from everywhere. Based on those past assumptions we figured limiting collection to convicts, voluntary submitters, and those we had probable cause for protected most folks privacy. An situation like this would be rare; if it did happen we probably would have permitted it; thinking the scope was highly limited, now it could easily pull most of us in.

 

Re:System worked, then?

[Idarubicin]

So here we have a guy where there is nothing at all to tie him to the events except DNA match that is actually exculpatory in that its clear he isn't a match for the sample the Police believe is that of the perps; however it does indicate he may be a family member however distant. The police want to confirm this. Is it reasonable to "search" his blood to confirm the match, and is that than cause to search everyone one of his relations, and their offspring?

Your summary may be a bit too brief for the nuances here. It appears that the police found a partial DNA match with the suspect's father (in, remarkably, a privately-maintained - not state-controlled - DNA database), which in turn suggested that a close relative would be match. The police then examined publicly-available genealogy information to identify candidate relatives. From the genealogy records the police narrowed their search to three candidate individuals. Using various other circumstantial information they finally sought a warrant to collect a DNA sample from just one individual.

While I agree that there are legitimate "slippery-slope" concerns, based on the (admittedly brief) description in the linked article, it seems that in this particular instance reasonable steps were taken to minimize the scope and inconvenience (to potentially-innocent individuals) of the investigation. It wasn't a scattershot "We must test the DNA of all your male relatives!", but rather "We want to test the DNA of your one male relative whom we also suspect for reasons (a), (b), and (c)."

Re:System worked, then?

[Half-pint HAL]

This isn't an abuse. This is the system working (as well as it can, though getting him in to the office on a lie is kind of skeevy). And since even the cleared suspect is considering the branches of his family tree even he's buying into the validity of the technique.

There was no concrete evidence, only circumstancial. I find it extremely worrying that he was brought in under false pretenses and that they granted a court order for the DNA sample before any request had been made to him for a voluntary submission.

Even if someone is your only suspect, he shouldn't be treated as a "prime suspect" without evidence. Usry says in the article that he was worried that they were going to push for charges even when the sample came back negative, and it was the police and FBI's treatment of him that made him worried. It wouldn't have been the first time that an overzealous law enforcement officer had got so fixated on "getting a result" that they would have pushed on, ignoring the evidence.

The biggest warning light in the article is actually an innocent-looking remark from the Sgt in the case: " “I wish it wasn’t a dead end, but it was.”" I know it's important to solve crimes, but no police officer should ever be disappointed to find out a suspect is innocent. Do you think that one-month wait was lab time? I doubt it. During all that time, some of the officers and agents involved may well have been pushing to continue, on the grounds that he probably passed through the town once, and they think it was a cousin of his, so they would be arguing that he "probably" drove his cousin up and was an accessory.

There is always the danger with these speculative searches that you end up identifying a suspect then convincing yourself he's the guy, then confirmation bias leads the officers to build a case around lots of selective evidence. In a cold case, you'd be essentially building a "loser edit" for the poor sod you've picked.

Re:System worked, then?

[Orgasmatron]

But they didn't suspect him at all. They found their suspect first, then constructed a circumstantial case (a, b and c) against him.

This is dangerous shit and the police should get slapped for it. And the public needs to step up and make it clear to judges that we won't tolerate them rubber stamping bullshit warrants. Just because there was a happy ending this time doesn't mean that we aren't playing with fire. This guy came one lab mistake away from from having his life ruined.

There was a time when most of us understood the dangers of working from desired conclusion to supporting facts. But now we celebrate people that work backwards, from cop shows on TV to "scientists" paid to push a political agenda.

Re:System worked, then?

[Immerman]

My understanding is that DNA matches are generally not accurate enough to be accepted by scientists as a conclusive match, though perhaps the techniques have improved since then. That's actually a big part of the problem with them - people believe them to be considerably more accurate than they actually are. Maybe they're even 99% accurate, but that would still mean that there's a 1 in 100 chance that you'll come up as a false positive: enough to worry about I'd say. And if the accuracy isn't even that good... well it makes DNA databases being used for identification a bit worrying. Not so much because they're not useful, but because the police, lawyers, judge, and jury all tend to believe that a match is far more conclusive than it really is. Especially the jury, whose familiarity with DNA evidence comes from daytime television, where it *always* fingers the guilty party.

Basically nobody involved is likely to have the grasp of statistics necessary to properly parse the results - even doctors, who you would expect to deal with false positives/negatives all the time often get it wrong. Test is 90% accurate, that means if you come up positive there's a 90% chance you've got the disease, right? Wrong. You also need to factor in the independent chance of actually having the disease. Say there's a 2% chance that a person chosen at random is infected: that means out of 100 people you will (on average) have 10 false positives and two actual positives: testing positive only means there's a 2/12 (17%) chance you're infected.

Now consider DNA evidence - let's be generous and say it's 99.999% accurate: there's 400 million people in the US, so you can expect there will be 400,000 false positives, only one of which actually be guilty. Me, I don't like those odds.

Re:Non Story

[Anonymous Coward]

No mistake was made. The police checked a potential suspect and cleared him.

Well, this should cause anyone using a DNA service or donating their DNA to science to think twice:

The elder Usry, who lives outside Jackson, Mississippi, said his DNA entered the equation through a project, sponsored years ago by the Mormon church, in which members gave DNA samples to the Sorenson Molecular Genealogy Foundation, a nonprofit whose forensic assets have been acquired by Ancestry.com, the world’s largest for-profit genealogy company.

What the actual fuck?