Fingerprint matching and gullibility

[Pup]

You wouldn't think fingerprint-matching experts would be this easy to influence. But it shows yet again how people's bias can affect their interpretation of evidence. It's from http://www.newscientist.com/article.ns?id=mg18725174.500

Fingerprint examiners can be heavily influenced by external factors when making judgements, according to research in which examiners were duped into thinking matching prints actually came from different people.

...

Dror and Péron arranged for five fingerprint examiners to determine whether a "latent" print matched an inked exemplar obtained from a suspect. A latent print is an impression left at a crime scene and visualised by a technique such a dusting. The examiners were also told by a colleague that these prints were the same ones that had notoriously and incorrectly been matched by FBI fingerprint examiners last year in the investigation into the Madrid bombings. That mismatch led to Portland lawyer Brandon Mayfield being incorrectly identified as one of the bombers.

What the three examiners didn't know was that the prints were not from the bombing case at all. Each pair of prints, different for each examiner, had previously been presented in court by that same expert as a definite match.

Yet in the experiment only one of the experts correctly deemed their pair as matches. "The other four participants changed their identification decision from the original decision they themselves had made five years earlier," says Dror. Three claimed the pair were a definite mismatch, while the fourth said there was insufficient information to make a definite decision...

[TobiasTheCommie]

This makes me just a bit scared.

[Pedro Gomes]

To me, fingerprint matching sounds like the sort of task that, some day, will be carried out by computers with such reliability that, in most cases, the results won’t need to be reviewed by humans. I wonder if the task involves any steps that absolutely require human judgement and cannot eventually be reproduced, for example, by a good (and perfectly unbiased) expert system. That Southampton study surely provides good reason to support research on automated systems for fingerprint matching.

[Bikewer]

To a large extent, it is now. We use the APHIS system, which returns reliable matches very quickly indeed.

Many years ago, when I was with the local county police, we had a crime-scene guy (nobody called them crime-scene technicians, criminalists, or any such thing back then. They were simply "ID" guys.) who was particularly good at rifling through stacks of print cards and making matches. He was a little strange....

[Pedro Gomes]

Originally posted by Bikewer
To a large extent, it is now. We use the APHIS system, which returns reliable matches very quickly indeed. (...)
Correct me if I'm wrong, but APHIS appears to be a funny acronym for the "Automated Palm, Fingerprint Identification System" from Cogent Systems (which they call CAPFIS (http://www.cogentsystems.com/products/)). Very interesting stuff. Just curious, who's "we"? (Don't really bother answering... ;))

[rjh01]

Allow me to ask the obvious question. How many people have been incorrectly convicted because of fingerprint evidence?

[Alkatran]

I wouldn't be worried about this: the story gives the impression that they thought it was a match. But they can't just ignore the information that they don't...

Now if they DIDN'T match and they were claimed as a match, THAT'S when you should be scared. You can't convict someone because their fingerprints don't match the killers!

[alfaniner]

I was caught by surprise at a bank where I don't have my account. I was depositing a business check and decided to cash a personal check I had. They took my thumbprint on the check --I've never had that done before. The last time I'd been fingerprinted was for my enlistment papers just before going to boot camp.

And I swear I will never do it for something so menial again.

[Bikewer]

I fear that increasingly it will be the case that some sort of biometric identifier will be necessary. The level of credit-card and check fraud is staggering, and right now the various banks and financial institutions are just "eating" a lot of it.

Sooner or later, just like bankruptcy "reform", they are going to require some sort of identifier.

[Rolfe]

Originally posted by rjh01
Allow me to ask the obvious question. How many people have been incorrectly convicted because of fingerprint evidence? Try putting "Shirley McKie" into the BBC news site, and read your way through the case. I got three pages of links on that site alone (http://newssearch.bbc.co.uk/cgi-bin/search/results.pl?scope=newsukfs&tab=news&q=Shirley+McKie+&go.x=27&go.y=14).

There was a lot of police corruption involved there, and goodness knows what the motivation for it all was, but basically some fingerprint "experts" were seriously out of line.

Oh, I see there is now a web site dedicated to the case (http://www.shirleymckie.com/).

Rolfe.

[Mensvoort]

An old discussion .. but nevertheless very interesting! And indeed a bit scary.

[Gene L]

Back in the day, it was difficult and required a WHOLE lot of skill. The FBI did almost all of it, and would send an expert to testify on any match. Matching prints was reviewed and any expert who missed five times in his career was fired. And not just in capital cases, but ANY case. Over a twenty or thirty year career, that's pretty demanding.

Now, it's done electronically (assuming electronic prints are available) and there is less of a human element in it. But 2009, electronic prints are required by law.

An electronic print enters a database where it can be retrieved based on points of identification. I don't know how many it takes to match a print, and I don't recall any case where there have been any mis-matches. Used to be, before computers and data storage, you had to have a suspect with prints and compare them to the print at the crime scene. Now, you can run them through the system and if there's a record on file, the computer will pick it up.

Ink prints are a lot more difficult to take because a slight error can smudge a print and make it invalid.

VERY few cases are solved with prints alone. Prints are hard to lift, for one thing. They are very good evidence, however.

[Mensvoort]

Thanks Gene L,

Interesting additional information. The electronic applications make this field much less scary.

[Gene L]

I don't think it's a problem, really. And before electronic data bases, fingerprints were not the end-all, they were evidence that was subject to a defense lawyer's rebuttal and of defense's own fingerprint experts. Photos of the prints were displayed in court with the areas of verification poined out. I don't know how many areas of identity it took, but there were several, if I recall.

Lawyers will frequently start movements or websites to help their clients out. They're trying to raise the level of doubt and since this is related to a specific case, I wouldn't doubt it a bit here.

One more thing: prints are not an indicator of guilt, only of presence. The common defense is to say, yes, the suspect was there but did not commit the crime.

Where interpretation plays a big part is with polygraphs. Of course, polygraphs are not admissable in court because of this. The data they gather is there, but the operator can read it wrong, or in some cases the one being tested can beat the system. If his body doesn't resond in the fashion the operator is expecting, it can give a mixed reading. A lack of guilt can mask if the person being tested actually did the act charged. It simply doesn't work with sociopaths.

Aldrich Ames is a good example.

[Soapy Sam]

Rolfe beat me to the http://www.shirleymckie.com/ link, but it bears repeating.
It's very understandable that police and police forensic people are trying to solve a case and achieve a conviction- and we put them under hellish pressure to do so, but forensic labs should be as blind and objective as any science, whether analysing fingerprints or any other data.
"No conclusion" is ALWAYS a valid answer.