Friday, March 20, 2009

Fingerprint examiner: Man of science or man of faith?

Forget everything you think you know about fingerprints. Please. It's all based on an assumption that has never really been tested, let alone proved. No one has ever actually established the assumption that all fingerprints are unique. But fingerprint examiners have been coming into courts for 100 years to identify defendants as culprits based on this assumption. Modern forensic scientists accept it as a matter of faith. But, of course, faith and science are mutually exclusive.

This opinion piece from the LA Times also mentions concerns about the smudged prints usually found at crime scenes. Often, they are only partial prints and they're often marred by other materials, like blood. And yet, fingerprint examiners often state in court that their results are practically infallible. The assumption they want us to make is that fingerprints are undeniable evidence of identity, just like DNA.

I know we've all been raised to know that fingerprint evidence is reliable evidence, based on sound science. And I know it's incredibly difficult to abandon those beliefs we've held since childhood. But I think it is time for us to acknowledge that what we have all accepted as undeniably true about fingerprint evidence is untested and deeply flawed.

I think it is time to start from scratch on fingerprints. First, we need to study and test the hypothesis that fingerprints really are unique. I know it seems natural to assume this, but science can't rest on assumptions. It needs to be rigorously tested. Next, a national consensus must be reached as to what constitutes a match. How many points of similarity need to be established before a fingerprint examiner can come into court and declare the bloody fingerprint belongs to the defendant? As it stands now, the number of matches is generally left up to each fingerprint examiner to decide for him or herself. Some rely on as few as 5 or 6 while some require far more. I would also like to see more serious scientific study into how reliable matching can be when dealing with partial, blurred, or smudged prints. Most crime scenes don't lend themselves to a defendant leaving behind a perfect, full, and pristine fingerprint.

In the meantime, if you're a juror in a criminal case, be a lot more skeptical about any fingerprint evidence you hear at trial. Don't just assume it's a valid science; make the state prove it to you.


DBB said...

I'd think that it would be really hard to question such things as a juror. If you just question the state's witnesses, they'll just swear up and down that the evidence is good and a match is a match. Where can you go after that? You can't call your own expert witnesses as a juror. The judge probalby will have no patience with a juror questioning "bedrock" principles like fingerprints. Likely, if you press on that, the only thing that would happen is, you'd be removed from the jury. I doubt you could even bring it up with fellow jurors in deliberations because problems with fingerprints would not have been introduced as evidence in the case.

This has special resonance for me right now as I am about to report for Jury duty tomorrow - though odds may not favor me actually being seated, because who wants a lawyer on the jury?

S said...

Yeah, I never understand why judges are so unwilling to let defense attorneys really explore this stuff in court.

But jurors are allowed to bring their common knowledge and experience into the jury room, right? So my goal is to make it common knowledge that our nation's crime labs and fingerprint examiners are full of it! :)

And, no, I can't imagine too many criminal defense attorneys make it on to juries, especially criminal ones.

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