Tainting Evidence: Behind the Scandals at the FBI Crime Lab.

• Author: Hansen, Mark C.

By John Kelly and Philip Wearne Simon and Schuster, $25

"If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue," an expert qualified by "knowledge, skill, experience, training, or education" can give an opinion. So say our rules of evidence. This opens the courtroom door to opinions from experts about, say, whether a defendant left his DNA on the bloody pavement, his John Hancock on a ransom note, or his senses before he committed the crime.

But what happens when experts aren't what they claim to be? That's the question posed in this book. The subject is the "forensic science" experts of the FBI crime labs: agents who specialize in things like trace analysis, ballistics, bomb reconstruction, even psychological profiling. The FBI has long enjoyed a reputation for solving crimes too slick for the local constabulary. But what did the feds know that the locals didn't? Not much, say the authors, who, as their title suggests, posit that the FBI was solving crimes by "tainting evidence" in its fabled crime lab. The result was phony evidence cooked up by pretend experts who were really just G-men in lab coats.

According to the authors, in 1996 the FBI lab staff of 694 handled 136,629 pieces of evidence and performed nearly 700,000 examinations. While screw-ups are not unique to the FBI (one county coroner, for example, lost a head), they were apparently endemic The problems ranged from the occasional "rogue" agent who made up credentials and tests, such as Special Agent Thomas Curran, who in 1974 lied about his degrees and the tests he had done, to more prosaic flaws in lab procedure. Without accepted standards and protocols to guide them, the bureau's men and women of science didn't document their work, didn't identify who did what, didn't do confirmatory testing, didn't sign, date, seal, and the like.

All of which was compounded by the pressure to make cases in court. Agents were not scrupulous in their science because, say the authors, they wanted to make the conclusions come out the right way and were loath to create paperwork that might undermine those conclusions. When they got to the witness stand, they often fudged the limits of their work, in effect painted over the gray with strong coats of rhetorical black. "Could have been" was transformed to "was," possibility became probability. The bureau hid this sorcery from the prying eyes of outside...