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License plate technology used to find Virginia shooter used in Central Pa.

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HARRISBURG, Pa. -- Dauphin County uses the same technology which helped Virginia police find the shooter following Wednesday's tragedy outside Roanoke.

Vester Lee Flanagan, the man who shot and killed WDBJ-TV reporter Alison Parker and photographer Adam Ward, had his rental car picked up by a license plate reader along Interstate 66 Wednesday. Law enforcement agencies in Dauphin County have been using the same technology for the past two years, according to District Attorney Ed Marsico.

"It makes it easier to catch criminals," he said. "Whether it’s a stolen car, stolen plate or someone being looked for like [Wednesday] in Virginia, it's information gathered quickly, seamlessly, and analyzed to allow police to find individuals who have committed crimes."

Dauphin County detective Andrew Dickson gave FOX43 a riding tour of how the license plate reading system works. Two cameras are mounted to the roof of the vehicle, and are connected to a computer inside. Each car which passes -- or gets passed by -- the license plate reader, gets its picture taken and is registered into a database. Dickson estimates a six-hour shift can wield 3,000-4,000 tags.

An image of the license plate reader used by Dauphin County detectives."Some of the best use we've had is when an incident takes place and you wonder, 'Why is that car here?'" D.A. Marsico said. "It's led to some leads and eventual arrests.

Dauphin County often times lends its license plate reader technology to other municipalities and counties. Its use, however, has the American Civil Liberties Union of Pennsylvania asking what is the line between safety and personal privacy?

"It's important that [law enforcement] uses them in a way that aids criminal investigations without violating peoples privacy," Andy Hoover, legislative director of the ACLU of PA said.

The ACLU is not opposed to the use of license plate reader, but cautions their overuse. They suggest databases are wiped clear at the end of daily shifts. A 2012 ACLU inquiry into the Washington County detectives in southwest Pennsylvania showed data acquired by license plate readers was being stored indefinitely, according to Hoover.

"That then leads to the potential of abuse," he said. "I know you went to the political event. I know what church, synagogue or mosque you went to.

"We don’t want our government tracking everywhere we go at every moment."

Marsico disagrees, saying the work done by license plate readers is no different than someone taking notes while walking through a city.

"I don’t see how there’s any privacy issue with this. These are cars, in lots, on the street," he said.

Cameras can be covert, hidden from plain sight, or overt, out in the open. Information obtained by the license plate reader is stored into a database which any law enforcement with access throughout the nation can obtain; "If a car is stolen in Missouri and it's on a side street here, it will pick it up," Dickson said.