This report discusses the The Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) firearms trace data. From the text: "A key component of ATF's enforcement mission is the tracing of firearms on behalf of thousands of Federal, State, local and foreign law enforcement agencies (LEA). Firearms trace data is critically important information developed by ATF to assist state and local law enforcement."
ATF Publication 3312.11
Bureau of Alcohol, Tobacco, Firearms and Explosives: http://www.atf.gov