Nothing cuts through the current hyperbole of forensic science reform debates and counter debates than reading what the “elite” of the FBI hair comparison people actually said in US courtrooms.
The following is testimonial evidence from an actual case.
Things to notice are:
1) affirmation and verification of this hair expert’s opinion is based on “personal experience.”
2) No mention of scientific studies is necessary. This is the typical Frye Rule which allows a court qualified expert to give an opinion with no foundation of empirically based research. He/she can say whatever is allowable by some “community of science” that teaches and truly believes that what they do is reliable. If enough of them exist, then admissibility by the courts is a slam dunk. It is amazing that so many of this “faith based” forensic techniques are still in use.
3) Along those same lines, the use of self-derived statistics is perfectly fine. This is seen in similar “matching” police forensics. As in bitemark identification.
4) Their mathematics of deception is based on multiplying the occurrence value (frequency) of each item of evidence (i.e how rare it is seen in a human population) times the number of times the evidence was recovered from the crime scene or victim. DNA profiling came along and actually was capable of doing this properly. It is called the product rule. It has been improperly used by bitemark experts since the 1980’s. Some groups have more recently abandoned this flim-flam. Others like fingerprints, just say that “no two fingerprints are alike.” The problem occurs when partial prints recovered from a scene are compared to a suspect’s own prints. The print people rely on a “peer review” of multiple examiners (at least one ) to independently analyse the evidence. That is not exactly science, but courts still love it.
5) The juries get a big kick out of hearing some piece of evidence is “unique.” Although unique is unscientific as well.
6) Appellate courts and prosecutors, who have come across cases like this, often say that although the methods are now considered flawed, the testimony given at the time of the trial was not “false.”
Here is an excerpt of the expert being questioned by the prosecution who hired him.
Q. Based upon your own personal experience, about what frequency have you found that hairs from different individuals might have the same microscopic characteristics?
A. Well, as I said earlier, it’s highly unlikely. Of the 10,000 individual hair exams I have done myself from approximately 10,000 different people I have only had two occasions, two different times I had hair from two different people I couldn’t distinguish. The closest I could give you in a number would be one in 5,000.
Q. In taking your experience as a hair examiner and the fact there were four individual separate hair transfers involved in this particular case, could you give the jury some idea of the probability of those individual hair transfers occurring between three separate individuals as you have found in the examination involved in this case?
A. Well, again, I found four separate hair transfers. Each one of them is what we call an independent event, independent of the other. If using my experience as a basis and as I said about one in 5,000, what you would have to do is take each event and multiply it times each other event.
[Analyst continues….] In other words, one in 5,000 times, one in 5,000 times, one in 5,000 times, one in 5,000. This would give you a number approximately 625 times 10 to the 12th power or 625 with 12 zeros behind it and I really don’t know what that number is.
Q. Based on what I know about math, that is a lot of numbers, more than a billion, more than a trillion?
A. Many more. It’s a quadrillion or something to that effect.
Junk science like this is why exoneration litigation is the only means available to counter the inertia of the legal system which resists acts of injustice and forensic exaggeration. Only a few prosecutors voluntarily step-up when obvious flawed testimony is brought forward during appeals. The experts saying these things rarely correct their past mistakes. Some claim, despite new evidence to the contrary that they are still ” protectors of the victims of crime.”
Others consider exonerations as sending “criminals back into society.” A for-profit advocate for government run crime labs uses this theory ( on a data-set of two cases ) to collect donations.