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December 15, 2002

'C.S.I.' Myth, The


In popular detective shows like ''C.S.I.,'' science almost always helps the cops nab the bad guy. But in the real world, two of the most respected tools of the crime-busting trade -- the polygraph machine and fingerprints -- are now being seriously questioned.

In October, the National Academy of Sciences released a study declaring that the polygraph machine is a woefully ''blunt instrument'' that has failed to ever catch a spy. Spooks like the infamous Aldrich Ames, the study concluded, can easily fool the supposedly unfoolable machine. Smooth criminals can apparently train themselves to beat the polygraph machine -- which measures pulse and breathing rates, sweating and blood pressure -- by using Valium and obscure muscular acrobatics involving their sphincters.

Fingerprints were subjected to a similarly brutal interrogation this year. In January, Judge Louis H. Pollak of Philadelphia ruled in a murder case that the use of fingerprint evidence should be limited; in his view, there was not enough proof that the procedure is reliable. It was the first legal challenge to the infallibility of fingerprinting in nearly a century.

The problem with fingerprinting is not the theory underlying it -- the whorled patterns are unique and unchanging throughout life -- but the clumsiness with which it's applied. Crime scenes do not yield clean, crisp prints. Detectives typically cull what is called a ''partial latent print,'' a smudged, bloody fragment that is often only 20 percent of the fingertip.

Consider a bitter fingerprint controversy in Britain involving Shirley McKie, a Scottish policewoman. McKie had been working on a murder case involving an elderly woman killed by her handyman. Detectives supposedly found a fingerprint belonging to McKie at the scene; McKie denied she was ever there. Later, two U.S. fingerprint experts corroborated her story. The culled print had been misread by British detectives. In the end, the matching of prints is an art rather than an exact science.

Pollak's ruling caused an immediate uproar. In response, the F.B.I. argued that it had never botched a fingerprint identification. (Indeed, a bloody fingerprint from a murderous robbery in Alabama helped capture the accused sniper John Lee Malvo.) Pollak ultimately reversed his decision in terms of allowing evidence, but still expressed deep concern that ''there have been at least a few instances in which fingerprint examiners, here and abroad, have made identifications that turned out to be erroneous.'' Until the F.B.I.'s standards become universal, then, the formerly sacrosanct fingerprint, like the polygraph, will be seen with newly skeptical eyes.

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