Your Fingerprints: Junk Science

When we were little children watching police shows like “The FBI” and “Adam-12” on TV, we became convinced, along with everyone else, that if a criminal’s fingerprints were found at the scene of the crime, it was case closed, proof-positive, open and shut.

Why? Because no two fingerprints, in the entire world, could be alike. How did we know that? How did we know that that was true? Because everyone acted as it it was true. Everyone acted as if no two fingers in the entire world could have matching patterns on them. Everyone acted as if this was the product of years of sound, thorough research conducted by revered scientists.

It is very odd, then, to discover, that there might never have been a good reason for believing that the evidentiary value of fingerprints has ever been established with any kind of scientific rigor. There really is no body of systematic research or scientific proof that fingerprints really are unique to each individual, at least, not in the way the movies and television would have you believe. In other words, nobody has ever systematically compared fingerprints to each other to establish just what the odds are that any two, from perfect strangers, might match.

In 1995, a proficiency test was administered to 156 law enforcement examiners. These are the guys called in to court to testify that the suspect’s prints — don’t forget, we could be talking about Lee Harvey Oswald here, among others– were found on the murder weapon, or a door knob, or a table surface, or something. Only 44% of these “experts” could correctly identify all five of a set of test prints. Read that again: less than half of the “experts” were proficient. And again: half of these guys got at least one of the prints wrong, out of five. Twenty percent. One in five.

I don’t know the details of the test, but I do know that the people who administered it considered the performance of half the experts to be inadequate and unreliable.

What has happened is that the Supreme Court of the United States has recently made some rulings that require courts to establish that “scientific evidence” really is scientific before it is allowed in the courtroom. What you have to imagine is some “expert” talking in obscure, difficult language about some scientific information which the jury doesn’t understand. The jury takes the guy’s word for it. The jury figures that the “expert” knows. The jury figures that he wouldn’t be testifying this way if he didn’t have a solid body of research and knowledge behind him. Think about fiber and hair analysis. Think about fingerprints. Think about those difficult cases where the prosecution actually has very little evidence so they scrounge around for “matching” fibers and hairs and semen and spots of blood. We have been trained by television and the movies to regard such evidence as definitive and decisive. Now we are beginning to know that such evidence can be constructed around a suspicion.

In France, 16 points of similarity, between fingerprints, are required before a “match” can be asserted. In Sweden, the number is 7. The FBI, in the U.S., won’t tell us how many it considers decisive. The FBI says it decides on a case by case basis. I thought that justice is exactly the opposite of that. Blind and impartial. Consistent. The FBI says, “trust me”. I wish I could.  Science does not provide standards that apply on a “case by case” basis.

Our system of justice– adversarial– encourages both sides to become advocates for their clients’ interests, rather than the truth. The police don’t just present facts– they invest in the suspect’s guilt, and advocate for it, and do whatever they feel needs to be done to “win” their case. It is apparent that often they feel that they know who did it– they just need to muster the facts necessary for a conviction. They sometimes regard the law as an impediment to justice.

They almost never willingly admit a mistake, even when DNA analysis proves they were wrong.

Occasionally, it is clear, they manufacture the “facts”. An expert, for example, will testify that a fiber found in the suspect’s car exactly matches a fiber taken from the victim’s sweater. So how do you assess the real degree of similarity, and the real likelihood that these fibers could have matched fibers from almost anyone else’s sweater? The lab is not presented with five samples and five potential matching fragments of evidence, and then asked to identify which ones match. They are presented with a set of fibres from the suspects home or clothing, and a set of fibres found at the crime scene. Do they match, yes or no? If no matches are found, we’ll find more fibres, and then more. The lab technician knows that the police will be happier if a match is found.

A suspect’s car– or any car– is loaded with smells, particles, dust, fragments of things, scraps of paper, coffee stains, oil and grease, residues, maybe even bodily fluids. If you took thousands of samples of every substance in a any car, how hard would it be to find something– anything– that matches something that can be linked to a victim– any victim? I’ll bet it wouldn’t be that hard at all.  Look at the Azaria Chamberlain case.

The Supreme Court is right. We should demand very high standards of “expert” testimony, before allowing smooth-talking partisan professionals to try to bowl over a jury with analysis that might well be nothing more than “junk science”.

Random Notes:

Until the 1880’s, the commonly accepted “age of consent” in America was 11.

2011-06: in the case of Casey Anthony, the prosecution is actually presenting “evidence” that traces of the smell of a decomposing body can be detected and analyzed from the trunk of Ms. Anthony’s car. This has all the hallmarks of the good old fibre analysis presented at so many cases by discredited forensic “scientists” in the past.

I hope her defense attorney has the intelligence to ask the prosecution to produce evidence of the smells of hundreds of cars compared to the smell captured from Ms. Anthony’s car and then have the “expert” blindly identify which one had the body in it.