In old-fashioned murder mysteries, the killer's sweaty palms always give him away. The intuitive detective -- attentive, adept at reading human nature -- quickly recognizes them as a sure sign of guilt.
Now, investigators say they require not intuition but DNA. They need only a drop of the sweat.
"When a person leaves any DNA at his crime scene, whether it's a drop of blood, saliva or perspiration, he's left us his calling card," says Paul Ferrara, a noted DNA researcher and head of Virginia's state crime laboratory, the Division of Forensic Science. "Just wearing a pair of gloves doesn't throw off the trail anymore."
Forensic science used to seem a simpler, less controversial discipline, as presented in the first manual on the subject, "The Washing Away of Wrongs," written in China in 1248. That book offered simple conclusions: Water in the lungs indicated drowning; pressure marks on the throat hinted at strangulation.
The field has advanced to the point that investigators can help identify a murderer by the insects on the corpse or a drop of saliva left behind by the killer. Fibers from a killer's gloves can be the breakthrough in a case, if there are traces of sweat on them. According to Ferrara, an important clue in a recent Virginia kidnapping case came from the perspiration on the band of a hat the abductor left behind.
"We surprise a lot of people with it," says Ferrara, describing the DNA analysis known as polymerase chain reaction, or PCR, which enables scientists to clone minute samples of DNA. "We've gotten DNA based on saliva from cigarette butts, saliva from the backs of envelopes, tissue from under the victim's fingernails, and from a portion of a hair follicle."
He and other forensic specialists have begun playing a greater role in crime investigations, based on sophisticated, sometimes controversial, methods of identifying criminals at their most basic level -- their genetic code.
Serologists used the saliva from an envelope flap of an tTC anonymous letter to link terrorist Nidal Ayyad to the 1993 World Trade Center bombing; Ayyad and others were later convicted. The FBI is also trying to link DNA from saliva on a postage stamp to the person accused of being the Unabomber, Theodore J. Kaczynski.
An advantage of PCR over older methods of DNA fingerprinting is that technicians can now analyze far smaller samples taken from bodily fluids.
