* Illustration: Wilson Hsu * In the summer of 2002, the FBI, the Baton Rouge Police Department, and several other agencies began a massive search for a serial killer suspected of murdering three women. Based on an FBI profile and an eyewitness report, they upended southern Louisiana looking for a white man who drives a white pickup, collecting DNA from more than 1,000 Caucasian males. They found nothing. Meanwhile, the killer struck again.

In March 2003, investigators turned to Tony Frudakis, a molecular biologist who said he could determine the suspect's race by analyzing his DNA. Uncertain about the science, the police asked Frudakis to take a blind test: They sent him DNA swabs from 20 people to see if he could identify their races. He nailed every one.

On a conference call a few weeks later, Frudakis reported his results on their killer. "Your guy could be African-American or Afro-Caribbean, but there is no chance that this is a Caucasian." There was a prolonged silence, followed by a flurry of questions. They all came down to this: Would Frudakis bet his life on his results? Absolutely.

Quickly changing course, the authorities soon turned up the file of Derrick Todd Lee, a 34-year-old black man with an extensive rap sheet for domestic violence, assault, stalking, and peeping. The police got a subpoena, took a cheek swab, and a few days later had an answer: Lee's sample matched DNA collected at the crime scenes.

Frudakis' test is called DNAWitness. It examines DNA from 176 locations along the genome. Particular sequences at these points are found primarily in people of African heritage, others mainly in people of Indo-European, Native American, or South Asian descent. No one sequence can perfectly identify a person's origin. But by looking at scores of markers, Frudakis says he can predict ancestry with a tiny margin of error.

Since the Baton Rouge case, DNAWitness has been used nationally in nearly 200 criminal investigations. In several, the science played a crucial role in narrowing the suspect field, ultimately leading to an arrest. But its success hasn't made the technology popular with law enforcement. Frudakis' company, DNAPrint, has yet to turn a profit and may not survive much longer.

Part of the problem is cost — basic tests run more than $1,000. But the real issue? DNAWitness touches on race and racial profiling — a subject with such a tortured history that people can't countenance the existence of the technology, even if they don't understand how it works.

"Once we start talking about predicting racial background from genetics, it's not much of a leap to talking about how people perform based on their DNA — why they committed that rape or stole that car or scored higher on that IQ test," says Troy Duster, former president of the American Sociological Association.

"This is analyzing data derived from a crime scene," Frudakis counters. "It's just a way for police to narrow down their suspect lists." But his position, rational as it may be, is no match for the emotions that surface with any pairing of race and crime.

Tony Clayton, a black man and a prosecutor who tried one of the Baton Rouge murder cases, concedes the benefits of the test: "Had it not been for Frudakis, we would still be looking for the white guy in the white pickup." Nevertheless, Clayton says he dislikes anything that implies we don't all "bleed the same blood." He adds, "If I could push a button and make this technology disappear, I would."

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