From The Wall Street Journal:

A federal agent proposed using license-plate readers to scan vehicles around gun shows in order to aid gun-trafficking investigations, according to an internal Justice Department email.

Justice Department officials said Tuesday that the 2009 proposal was rejected by superiors and never implemented. The email was part of a series of Drug Enforcement Administration documents describing how the agency is building a national database tracking the movements of vehicles in the U.S. The documents were obtained by the American Civil Liberties Union through a Freedom of Information Act request and reviewed by The Wall Street Journal.