In 1999, more than 150,000 firearms were submitted by law-enforcement agencies for tracing by the Bureau of Alcohol, Tobacco, and Firearms (ATF), three times as many as in 1993.'This growth in trace requests indicates the success of ATF's program to persuade state and local agencies of the strategic value of comprehensive firearms tracing. About four dozen cities now submit all firearms confiscated by the police for tracing, and the growing database of trace results has provided the raw material for improved intelligence on the channels by which guns are acquired by criminals. But the proper interpretation and use of these data remains controversial.

Firearms tracing is nothing new. The Gun Control Act of 19682 established the regulations that make it possible, at least in principle, to determine the chain of commerce for a firearm from the point of import or manufacture to the first retail sale. 3 Best practice in a police investigation of a gun homicide or assault often includes submitting the gun (if available) for tracing, in the hope of