Fingerprints
- Randy Justus
- Jan 30, 2022
- 2 min read
This is going to be shocking to some people. Fingerprint evidence is NOT 100% accurate.
That’s not what we’ve been taught by television. Just watch any of the popular fiction and non-fiction crime shows and you see a CSI run them through a machine and presto change-o you have you suspect. Not so fast. The truth about fingerprint science is quite different.
There are fingerprint scanners that can do a great job if the person being fingerprinted has their fingerprints on file. The problem is with latent fingerprints gathered from a crime scene. What happens is that a human fingerprint examiner with a magnifying glass compares the latent print to prints in the system to determine a match.
Fingerprint examiners will tell you that fingerprints are infallible.
Cognitive neuroscientist Itiel Dror designed a study to see if fingerprint examiners' decisions on matches might unconsciously be biased by information they received about a case.
While have coffee with Dave Charlton a veteran fingerprint examiner, supervisor of a U.K. police departments fingerprint lab and editor of the Fingerprint Society's journal Fingerprint World agreed to put Dror’s theory to the test.
Five international experts were put to the test not knowing they would be re-examining matched prints from their own old cases while armed with different — and potentially biasing — "case information."
Most of the experts changed their minds on their previously determined matches.[i]
There was a 2011 study that found there was a false positive rate of 0.1% false positives. That doesn’t sound like a lot, does it? When you realize that 0.1 percent of the FBI’s annual fingerprint intake is 60,000 people, or 60,000 potential false positive IDs.[ii]
There was a report that was done by the American Association for the Advancement of Science that states, “We have concluded that latent print examiners should avoid claiming that they can associate a latent print with a single source and should particularly avoid claiming or implying that they can do so infallibly, with 100% accuracy,” states the report.[iii]
What’s the consequences of these mistakes? Let’s look at some actual cases.
In 1998 Stephen Cowen was convicted of murder after the prosecution and their fingerprint experts claimed that fingerprints found at the scene of the crime couldn’t have come from anyone else. In 2004, the police and prosecutors admitted they were wrong. Six and a half years is a long time to spend in prison for a crime you didn’t commit.
What about Brandon Mayfield? Mayfield was an Oregon lawyer, who spent two weeks in jail in 2004 because three FBI experts matched his prints with those found on a plastic bag that was evidence in the investigation of the Madrid train bombings. Spanish authorities continued to try to match the prints after the FBI arrested Mayfield and eventually linked them to an Algerian man. Thank god for the Spanish authorities.
Crime scene prints usually consist of only about 20% of the fingertip and they are often smudged. Examiners link a partial print from a crime scene to a whole one taken from a suspect by matching characteristics of the fingerprint.
So, the real question is, how many innocent people have been convicted of false positive fingerprint matches?
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