The perfect crime may be a thing of the past, now that DNA testing can identify a person by hair, a speck of skin or a drop of saliva. But is this science to be feared?

TRACES OF YOU

August 13, 1998|By Robert Guy Matthews | Robert Guy Matthews,SUN STAFF

The man who pumped bullets into the heads of two Annapolis lawyers in 1994 was careful to leave no witnesses, no weapon, and no fingerprints. He was thirsty, though. And that was what eventually did him in.

The streak of saliva Scotland E. Williams left behind after taking a swig from a water glass sitting on a kitchen counter betrayed him. On the glass was enough of his DNA for police to put him at the crime scene, and Williams was convicted of the double-murder last spring.

These days, it doesn't take much to thwart what might have been the perfect murder only 10 years ago. Just a drop of saliva, a spot of blood or a couple of strands of hair and there it is, all that is unique to you, bathing in the light of a microscope.

DNA testing has the potential to make a liar out of the president of the United States. To expose a mix-up of newborns at a Virginia hospital three years ago. To give a name to remains in the Tomb of the Unknown Soldier.

This decade-old forensic science is leaving its own mark on the culture. Some welcome it as the best crime-fighting technique since the fingerprint match. Others curse it, calling it a black art and statistical voodoo that, if used nefariously, could undermine each individual's right to privacy.

"People are fascinated, terrified, appalled and befuddled when it comes to genetics and DNA testing," says Arthur Caplan, director for the Center for Bioethics at the University of Pennsylvania. "Finding out that scientists are testing our DNA takes away some certainty that our identity is inviolate, secret."

As the nation waits for the FBI to reveal whether President Clinton may have left evidence of his DNA on Monica Lewinky's dress, perhaps proving a sexual relationship, debates over the ethical and scientific uses of genetic testing have been reignited.

Not since the O.J. Simpson murder trial and its infamous bloody glove and socks have people been so preoccupied with DNA testing.

"It makes me nervous," says Diane Silverstein, a Baltimore County juror who voted to convict a man for murder after police found his saliva on a cigarette butt near the victim's body. "I feel like I am a slave to some lab technician. If he does something wrong, looks at something askance, I could be pinned for a murder or anything else."

Silverstein, 47, isn't given to believe in conspiracy theories, she says. But even after her court experience, she doesn't understand just how DNA testing works. It's too "sci-fi," she says, and that makes her suspicious.

"Just how far will it all go? What do I do if I'm mugged? Snatch a strand of hair from his beard and trot down to the police station and tell them, 'This is the guy you want. Now go get him?' "

Not quite, but maybe some day soon.

Much is still misunderstood about how conclusively DNA testing can point a definitive finger at suspect.

"It is not perfect," says Michael Baird, vice president of laboratory operations at Lifecodes Corp., a pioneer biotechnology company that specializes in DNA testing. "It's not as good as a fingerprint."

The odds

So far, DNA testing is an odds-maker. It can't say definitively that two samples match. Instead it offers odds that two samples have a good chance of being from the same source. Of course, in some cases, the odds that the science is wrong are astronomical. A one-in-a-million chance that two samples don't match is a long shot indeed, but there is always that tiny chance looming.

Many things have to go right before a DNA test can be used. Hair has to contain the root or it is useless. Blood and other bodily fluid samples can be ruined if they are mixed with blood and fluids from another source. A sample can be too small to measure.

But DNA testing also isn't as delicate as many think.

Pathologists and scientists are amazingly adept in re-creating a person's DNA blueprint. Blood, even if dried or old, is still an excellent sample. The same goes for semen and saliva. Hairs are almost always present when two people come in contact. The minute samples of DNA are then cloned and built into a profile.

So, theoretically, could Clinton's DNA still be found on Lewinsky's dress, even if the dress had been dry cleaned?

Absolutely, say DNA experts. It depends on what chemicals were used in the cleaning process. There could still be enough DNA present to suggest that he and the White House intern had sexual contact.

"You can try to blow up your evidence, or wash it away, or dispose of a victim's body, or just pray that nothing will ever be found," says David L. Brody, chief or the Boston Police Department Crime Lab Unit. "But we'll still find or reconstruct virtually anything to a microscopic degree."

The champions of DNA testing are most always scientists and law enforcement agencies. But DNA testing is used in more than just criminal cases.

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