Ballistics fingerprinting got a sudden publicity boost this fall during the Washington-area sniping spree. ”If police in the sniper case could have traced the gun to the shop in Tacoma, Wash., where it was bought,” says Matt Bennett of Americans for Gun Safety, ”they would have been able to start looking in the Tacoma area much earlier.” Xavier Becerra, a Democratic congressman in California, has introduced federal legislation to create a bullet-identification system, and several states, including New Jersey, California, Connecticut and Massachusetts, began weighing their own versions of such laws.

The idea is not entirely new. Since 1996, the Bureau of Alcohol, Tobacco and Firearms has used a bullet-identification system to compare bullets or shell casings from guns used in crimes. Indeed, the A.T.F. is proud enough of its success with the system to run a feature on its Web site called ”Hits of the Week,” which highlights crimes solved through ballistics identification.