Virginia State Police recorded the license plates of vehicles headed from Virginia to President Barack Obama's first inauguration in 2009, and to some campaign rallies the previous fall, reports the Richmond Times-Dispatch.
The actions came after a request from the U.S. Secret Service, who asked that police use an automated license plate reader at the entrance to the Pentagon as an extra level of security.
They also recorded license plates of those attending campaign rallies for Obama and Republican vice presidential nominee Sarah Palin three months earlier.
The Times-Dispatch reports: "The license plate readers requested for the political events 'would detect any stolen vehicles attempting to enter the outer perimeter of the event and possibly allow for some record of attendees in the event that a serious [incident] occurred,' a state police sergeant wrote in a 2009 letter that outlined some of the department's uses for the license plate reader technology."
Virginia has used automatic police license readers since 2006, mostly to detect stolen cars and fugitives. The data collected was also used to solve other crimes by letting law enforcement officials connect a suspect to a specific place and time.
Until recently, state police stored images of roughly eight million license plates, some for up to three years, on a server in Chesterfield County. The data was dumped in March following a legal opinion issued by Virginia Attorney General Ken Cuccinelli.
License plate data is still being collected, but it's automatically deleted in 24 hours unless it's needed as part of an ongoing investigation, Virginia State Police Sgt. Robert Alessi told the Times-Dispatch.
The American Civil Liberties Union (ACLU) has criticized the collection of such data in a report, saying it's invasive and discriminatory.
"While it is legitimate to use license plate readers to identify those who are alleged to have committed crimes, the overwhelming majority of people whose movements are monitored and recorded by these machines are innocent, and there is no reason for the police to be keeping records on their movements," the report says. "Ordinary people going about their daily lives have every right to expect that their movements will not be logged into massive government databases."
The ACLU also blames the federal government for "fueling" state and local use of license plate readers by providing grants to purchase the readers.
In a 2011 survey, almost three-quarters of polled police agencies reported using license plate readers, with 85 percent planning to increase their use of them in the coming years, the ALCU report said.
