Some police departments in Connecticut that use license plate scanning technology to identify unregistered and stolen cars are holding on to the data and sharing it, raising privacy concerns about how that information could be used.
"By allowing the police to keep them [the license plate data] indefinitely and then searching them however they want ... it's like retroactive surveillance without probable cause," said David J. McGuire, the American Civil Liberties Union staff attorney who requested the data.
"We know that this is a legitimate law-enforcement tool," he said. "What we're saying is that it should be regulated and there should be some oversight."
The scanning database was first reported on Tuesday by The Associated Press.
A group of 10 towns pooled their scans to compile a database with more than 3.1 million records on more than 1.3 million different vehicles since October 2009. A license plate was captured on average once every 14 1/2 seconds; on the busiest day, police captured 13,597 plates.
The scanners, mounted in police cars, allow officers to instantly identity cars that are stolen or unregistered, or are linked to criminal activity. But the vast majority of the license plates scanned are on vehicles with no problems, and the data can show when and where those cars have been.
The ACLU is pushing a bill that would prohibit police from keeping the data for longer than two weeks, unless specific pieces of information are needed for an active investigation. Maine has a law setting a three-week limit on keeping the data, McGuire said. New Hampshire law bans the scanners altogether.
The ubiquity of the scanners is evident in a map that the ACLU created showing license-plate scans around the Buckland Hills mall in Manchester last November. Red dots blanket multiple approach routes and thousands of parking spaces.
"I understand why [police] want it. It's incredibly powerful. It's a lot of information," McGuire said. "But at the same time, people have a reasonable expectation of privacy. For example, all the people that were in the mall in November shopping didn't think they were having their plates scanned and put in a database forever."