Shannon Kohler doesn't even drive a white pickup truck. Yet police singled him out anyway, in one of America's largest DNA dragnets to date.

Authorities say sightings of a white pickup truck, along with DNA evidence, connect the brutal murders of four women found since September 2001 along Louisiana's back roads - and could be tied to a fifth murder, a woman nabbed on Christmas Eve from a Subway parking lot across the Mississippi River from here.

Mr. Kohler, who drives a wrecked Dodge sedan with a red stripe and has phone records proving he was home when the murders occurred, is not a suspect. Police targeted him on the basis of anonymous tips, an old burglary conviction, and the fact that he'd once worked on a street where the first victim's cellphone was found. But his swift protest against the test - a cheek swab - and a clerical slip in the court record that made his name public, have put him at the center of a larger feud over privacy, DNA dragnets, and an expanding genetic database that, critics fear, could become a genomic version of Big Brother.

The request for DNA, says Mr. Kohler, is "a Fourth Amendment violation" - a breach of his protection against unreasonable search and seizure.

But to local police, it's a desperate strategy in a puzzling case: a serial killer who chooses victims with no clear regard for age, race, or habits. In Louisiana, nearly 1,000 men have been tested for a DNA match - mostly on the basis of anonymous tips - and close to 800 have been cleared. Because time is critical, says West Baton Rouge chief deputy Mike Cazes, most have willingly complied. "Anybody that's been approached ..., and [the officer] explains why - most of them say, 'Sure, I'd be happy to.' " In light of such cooperation, those who hesitate - as did Kohler and 14 others - draw swift notice. "A court order would be issued immediately," says Mr. Cazes, "and they would be swabbed."

Critics fear such sweeps could lead to coercion, as police persuade vast numbers to take these tests. That in turn, creates new quandaries: the possibility of harassing the innocent, and the potential to violate suspects' rights against search and seizure.

Some experts fear that, with DNA forensic databanks now authorized nationwide, practices for evidence collection are evolving in a vacuum, with little precedent or supervision. Should the government keep on file the DNA of the innocent? Could that "evidence" come back to haunt them in future (or prior) crimes? And even beyond DNA's criminal applications, could employers, or others, access genetic profiles and weigh them in hiring decisions, steering clear of employees with medical liabilities?

"A tremendous change is afoot in criminal justice," says Philip Reilly, president and CEO of Interleukin Genetics. "It is loaded with opportunities and fraught with problems."

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