In what officials say is the nation's first such countywide effort, Bucks County police departments announced Tuesday that they have created a database of DNA samples collected from accused or suspected criminals.

The mouth swabs for the database are collected on a voluntary basis, with police requesting them from those who have been arrested or from suspects.

The aim is to catch criminals who often fly under the radar of national and state DNA databases, which contain the genetic material of more hardened felons and sex offenders forced to submit DNA samples. But local collections are often unregulated, and the American Civil Liberties Union says the DNA-collection trend "represents a grave threat to privacy."

In Bucks County, suspects sign a form stating that the DNA swabs are consensual.

"We have to do what we have to do to solve crimes," Fred Harran, public safety director of Bensalem, said at a news conference.

Bensalem operates its own voluntary DNA database, collecting about 13,000 samples that have resulted in more than 400 arrests since 2010. Only about 5 percent have refused to cooperate, and fewer asked police to destroy samples at a later date, Harran said.

Showcasing the database's efficacy on Tuesday, Harran cited Ian Dougherty, 34, of Philadelphia. The database led to his arrest on burglary charges in May after he cut himself while breaking into a Bensalem home, police said. Two months later, he was suspected of breaking into a Lower Gwynedd home. But blood found on a jewelry box matched someone else's, Harran said.

Other police departments across the country have similar databases. But Bucks officials say this is the nation's first countywide collection, involving all 40 of the county's police departments.

The database "adds to our crime-fighting tools," said Matt Weintraub, chief of prosecutions in Bucks County. "It's not a gun. It's not a Taser. It's not even a weapon. It's a Q-tip. And because of that, we're a much more safe community."

The collection will cost about $600,000 a year to operate, shared by the county and the towns. The database will be maintained by the Virginia-based company Bode Cellmark Forensics.

All states require convicted felons to submit DNA, according to a Congressional Research Service report. And most, including Pennsylvania and New Jersey, require misdemeanor sex offenders to provide swabs, as well.

But 30 states, including New Jersey, allow police to take DNA from people arrested, but not charged, for serious crimes such as murder and sexual offense, according to the National Conference of State Legislatures. A pending bill would grant similar powers in Pennsylvania.

The increase in voluntary DNA databases has been spurred, at least in part, by a 2013 U.S. Supreme Court ruling that police can collect DNA from people arrested - but not charged - for serious crimes.

The court decision does not explicitly address databases consisting of voluntary DNA samples. But legal experts believe the ruling approves the use of DNA by police to identify suspects and others in the same way fingerprints have been used for decades.

David Kairys, a Philadelphia-based civil rights attorney and Temple University law professor, said an implicit coercion comes from a police officer's asking for a swab.

"The police have an enormous amount of power when they bring you in," he said. "And even if it's not said, they want you to do this. It's kind of like saying 'You don't need a lawyer if you're not guilty.' "

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