The CSI Effect: The truth about forensic science
The New Yorker
May 7, 2007

On the evening of March 10, 2003, two New York Police Department detectives, James V. Nemorin and Rodney J. Andrews, were shot and killed in an unmarked police car while attempting an undercover purchase of a Tec-9 assault pistol on Staten Island. The case was significant not just because two officers had died but because the man who was eventually charged with the murders, Ronell Wilson, faced the possibility of becoming the first person in more than fifty years to be executed for a crime in New York State.

The government's theory was that Wilson, who was with an accomplice in the back seat of the car, shot the detectives during a robbery attempt. Among the evidence retrieved from the crime scene were hundreds of hairs and fibres, and prosecutors enlisted Lisa Faber, a criminalist and the supervisor of the N.Y.P.D. crime lab's hair-and-fibre unit, to testify at Wilson's trial, last winter. Under questioning in Brooklyn federal court, Faber said that she had compared samples of fabric from the detectives' car with fibres found on gloves, jeans, and a baseball cap that Wilson had allegedly been wearing on the night of the crime. The prosecutor asked Faber to describe the methods and equipment she had used to make her analysis. Then she asked Faber what she had found. "My conclusion is that all of those questioned fibres could have originated from the interior of the Nissan Maxima, from the seats, and/or the backrests," Faber said. She added that in her field "the strongest association you can say is that 'it could have come from' " the source in question.

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"With trace analysis, what we are doing is comparing a 'q' to a 'k,' " Faber told the group. "A 'q' is a questioned sample from a crime scene-a paint chip on someone's clothing from a hit and run, a hair in the hand of a murder victim. The source is unknown. The 'k' is a known sample-a hair from the autopsy, or one that you take from a suspect. What we do in the trace-analysis unit are comparisons with 'q's and 'k's. We see if there is a connection."

Faber's brief summary defined the dilemma at the heart of forensic science. "There are really two kinds of forensic science," says Michael J. Saks, a professor of law and psychology at Arizona State University, and a prominent critic of the way such science is used in courtrooms. "The first is very straightforward. It says, 'We have a dead body. Let's see what chemicals are in the blood. Is there alcohol? Cocaine?' That is real science applied to a forensics problem. The other half of forensic science has been invented by and for police departments, and that includes finger-prints, handwriting, tool marks, tire marks, hair and fibre. All of those essentially share one belief, which is that there are no two specimens that are alike except those from the same source." Saks and other experts argue that there is no objective basis for making the link between a "q" and a "k." "There is no scientific evidence, no validation studies, or anything else that scientists usually demand, for that proposition-that, say, two hairs that look alike came from the same person," Saks said. "It's the individualization fallacy, and it's not real science. It's faith-based science."

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