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Fingerprinting gaining fallibility

By imrdkl in News
Sat Mar 02, 2002 at 02:22:39 PM EST
Tags: News (all tags)

The subject of fingerprinting, and it's potential for error in criminal cases was covered here almost two years ago, with a link to this article, which covers a persons court refutation (as an expert witness) of the science and statistical validity of the assertions associated with fingerprint identification.

Last month, a judge agreed with the premises in that article, and established for the first time that fingerprinting evidence could not be declared as a "match". Now there are a whole lot of people scrambling to get him to change his mind.

The ruling, which is being called everything from revolutionary to crackpot, could change the ways in which forensic evidence is collected and presented in criminal trials, and reduce what was once considered infallible proof, to corroborating evidence.

The primary argument against the infallibility of fingerprint identification comes with the possibility of errors made in the comparison of a persons fingerprint with another, based upon a specific "point-algorithm", where whorls, lines, or loops are matched up. This process is generally now considered to be more of an art, than a science, even if the other premises which underly an fingerprint identification have not been invalidated. E.g. - fingerprints dont change in a lifetime, and fingerprints are all different.

The other major concern is the level of training afforded the typical fingerprint examiner. According to some opinions, the tests given by the FBI are too easy. Watch the news for more on the Judge Pollak's assault on this time-honored technique for catching bad guys.


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Fingerprints are
o incontrovertable 1%
o corroborating 44%
o inadmissable 3%
o on the damn bathroom mirror again 50%

Votes: 59
Results | Other Polls

Related Links
o covered
o this article
o agreed
o scrambling
o art
o some opinions
o Judge Pollak's assault
o Also by imrdkl

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Fingerprinting gaining fallibility | 10 comments (8 topical, 2 editorial, 0 hidden)
We really need a scientific study (4.50 / 8) (#2)
by Secret Coward on Sat Mar 02, 2002 at 07:18:17 AM EST

I've heard that the FBI's computers return a list of the top five or so likely matches, and then a human compares likely suspects' prints to the sample. This does not leave me at all confident in fingerprint analysis.

Does anyone know of any controlled studies that took latent prints and sent them in for a match? It would be interesting to see the results.

If the typical latent print is partial or smudged, it is mighty difficult to claim that the partial print is unique. Sir Francis Galton claimed that 1-in-64 billion prints is a duplicate. Thirty-six bits represents 68 Billion numbers. If we only have half as much data (18 bits, or half of a fingerprint), we can only represent 260,000 numbers. In a nation of 260 million people, the partial print would typically match 1000 suspects (assuming there is no duplicate data in that half print). Even worse, if the print is slightly, but no noticably smudged, the sample might not even match the finger it came from; thus all 1000 suspects are innocent.

Finally, finger prints are completely useless if they were at the scene for an innocent reason. Just because my prints were on the kitchen knife, doesn't mean I stabbed my wife.

This reminds me of a study on DNA. Researchers took DNA samples from 50 people. They sent the samples to a lab to be matched up. The results came back, and the lab incorrectly matched two samples. If the foresics experts have a failure rate of 4%, it doesn't matter if everyone has unique DNA (which they don't). Even if the foresics experts were perfect, and everyone did have unique DNA, we still do not know if the section of DNA that we sample is unique for each person (i.e. does it match other family members or persons of similar cultures).

Analogy (4.50 / 2) (#9)
by fluffy grue on Sat Mar 02, 2002 at 08:38:25 PM EST

Your "bitwise" analogy is a bit flawed, in that half of a fingerprint might not necessarily be equivalent to half of a bitwise representation for that fingerprint. IIRC, the fingerprint isn't matched based on the image directly, but on the location of key features (forks, whorls, ridge spacing, etc.). So, your hand-wavey pseudo-math doesn't really hold any water.

However, the point about presence being irrelevant is quite true. When I watched The Fugitive (the Harrison Ford movie version; I still haven't seen the original TV series) for the first time, when one of the investigators said, "His fingerprints were all over the place!" I couldn't help but complain, "It's his house!" I couldn't believe that any real-world investigator would use that tenuous argument. However, I can't help but wonder if real-world investigators would be that stupid...
"Is not a quine" is not a quine.
I have a master's degree in science!

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[ Parent ]

Art, not a science (4.00 / 7) (#3)
by itrebax on Sat Mar 02, 2002 at 10:57:28 AM EST

I saw a show on history, discovery, or TLC (the "good" channels) a few months ago that was discussing fingerprinting. Basically, it said that fingerprinting was always an art, but the courts turned it into a science, especially with the dawn of fingerprint databases.

Effects on other cases? (4.66 / 3) (#5)
by rusty on Sat Mar 02, 2002 at 12:13:47 PM EST

If this ruling is considered precedent, what kind of effect could this have on the legal system as a whole? How many people are behind bars right now based solely, or primarily, on fingerprint evidence? Couldn't they all conceivably file for a new trial with the premise that if fingerprints are not "proof", they have been wrongfully found guilty?

Not the real rusty
If the judgement stands (4.00 / 1) (#6)
by imrdkl on Sat Mar 02, 2002 at 01:34:59 PM EST

it might lead to reopening of some older cases where the fingerprint "match" was prima facie (I like saying that, prima facie =) evidence in the conviction.

[ Parent ]
If they're still alive (none / 0) (#10)
by Macrobat on Sun Mar 03, 2002 at 01:50:50 PM EST

Couldn't they all conceivably file for a new trial with the premise that if fingerprints are not "proof", they have been wrongfully found guilty?

The ones who are still behind bars, maybe. If they've been executed for a capital crime, well, no.

"Hardly used" will not fetch a better price for your brain.
[ Parent ]

Forensic Science (4.20 / 5) (#7)
by SIGFPE on Sat Mar 02, 2002 at 04:34:27 PM EST

I have a deep mistrust of forensic science. One has to remember that workers in law and law enforcement: judges, juries, police officers and lawyers, generally lack even basic training in science and probability theory. There are many different pieces of evidence that can go together in a court case and the way to combine different pieces of evidence is probability theory. Without a grounding in the subject it seems ridiculous to let people loose with evidence like fingerprint evidence or DNA evidence. But that is a separate issue from my mistrust of forensic science.

I think that from time to time forensic scientists need to be independently tested. Crazy ideas for tests that come to mind include things like: someone builds a bomb from fertilizer, is given an opportunity to thoroughly clean themselves up, and then a forensic scientist has to identify them from a group of 9 other people by testing swabs from the people's skin. Real world tests of known situations. Not tests under carefully controlled conditions or tests based on self supporting evidence (like: this bit of science 'demonstrates' X is was at scene of crime in court and we know this science is good because the ultimately jury convicted X).

Curses (5.00 / 5) (#8)
by onyxruby on Sat Mar 02, 2002 at 06:38:18 PM EST

I was going to write an article on this, and you beat me to it. Oh well, good article, but I would like to add some more information to this that I picked up. The first resource I was using is a book called Suspect Identities, a history of fingerprinting and criminal identification Harvard University Press Copyright 2001 ISBN 0-674-00455-8 Simone Cole PHD.

The book debunks the fingerprint and shows that among other things it has no scientific basis or value. Quite literally the fingerprint has never been scientifically scrutinized. It exists on reputation alone, unable to meet the strict US Court of Appeals guidelines from Frye v. United States (1923) - U.S. Court of Appeals of District of Columbia demanding that evidence be scientifically validated. The US Supreme Court has also demanded that evidence presented in a courtroom be scientifically sound in Daubert v. Merrell Dow Pharmaceuticals (1993) and Kumho Tire v. Carmichael (1999). The questioning of such techniques is also happening abroad, notably in the case of

Detective Constable Shirley McKie, 37, who was charged with perjury after fingerprint experts wrongly claimed she was at the scene of a murder in Kilmarnock in 1997.
She was put into prison based on a 14 point match. To put this into perspective, most US police departments use anywhere from 8 to 12 such points. The FBI itself only requires as few as six such points to match. There is no consistent standard for a minimum number of such points in the US.

One excellent article on this subject is by Simon Cole, published on LinguaFranca To blockquote his article:

Perhaps anticipating such challenges, the Federal Bureau of Investigation made an eleventh-hour dash for empirical validation. In February 1999, Stephen Meagher, a supervisory fingerprint specialist at the FBI, sent a letter to all fifty state crime laboratories that began, "The FBI needs your immediate help!" Enclosed were copies of the two latent prints from the getaway car and an inked fingerprint card containing a full set of Mitchell's ten fingerprints. The respondents were to examine the latents in order to determine whether they matched any of the prints on the card. The idea, presumably, was to show that latent print identification was objective by demonstrating that different practitioners would agree on whether or not the prints matched.

But rather than clarifying matters, Meagher's survey added yet another wrinkle to the case. Seven laboratories failed to match one of the latent prints with Mitchell's inked prints, and five failed to match the second latent print. Suddenly, Epstein had a number of qualified FPEs who said that the latents from the getaway car could not be positively identified as Mitchell's prints. The prosecution had a problem.

At present, it is only a matter of time before inevitable death bell for the fingerprint rings.

The moon is covered with the results of astronomical odds.

Fingerprinting gaining fallibility | 10 comments (8 topical, 2 editorial, 0 hidden)
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