Morris Samuel “Sam” Clark was the head of the FBI’s hair unit when it began training state and local analysts in 1973. He said he long believed that examiners could trace hairs from a crime scene to a particular person with a high degree of probability — even though there is no scientific proof that is possible.
But Clark, who did graduate work in biology at Harvard and retired in 1979, said laboratory experience should not be discounted. He did “hundreds and hundreds of comparisons” over nearly 20 years, and he believes that he was a qualified court expert, he said in an interview from his home in Spotsylvania County.
The FBI’s training regimen, which required agents to compare hairs side-by-side under high-powered microscopes for a year before working on live cases, gave lab veterans confidence that they could tell the difference between individuals’ hairs just as an ordinary person could distinguish between their faces.
They embraced a set of vague standards. In written lab reports, FBI agents would include the caveat that hair examination was not a basis for positive identification.
In court, however, they could suggest that it would be highly unlikely for an examiner’s match to be wrong. The bureau left it up to individual labs and examiners to explain matters to jurors. Agents were trained to say that in their “personal experience” they had rarely seen hairs from different people that looked alike.
That evolved into jurors’ hearing numbers that had a huge impact even if they lacked scientific grounding. After a slaying in Tennessee in 1980, an FBI agent testified in a capital case that there was one chance in 4,500 or 5,000 that a hair came from someone other than the suspect.
But as experts from around the world would later note, the FBI-taught answer was misleading. In reality, FBI examiners did not compare every hair to every other hair they had ever examined. They simply compared crime-scene hairs and hair samples from individuals relevant in each case.
Examiners kept no “database” of samples, which went back to police evidence files. And differences between hairs are so fine that a person can generally keep only a handful of hairs in mind at any time.
“The claim you could keep all those hairs in your head and sort them in your mind, that would be hard to do,” said Mark R. Wilson, a 23-year FBI veteran who helped develop DNA testing for hair in 1996. “After about three or four [hairs], it gets confusing.”
The claim was called into question at an international conference hosted by the FBI in 1985, but the training was not overhauled for at least a dozen more years.