"...Forensic testing of ammunition used in a crime is the most effective way of tracing criminal activity."
-- Governor Arnold Schwarzenegger (R-CA)

Ballistic identification is the science of using a ballistic fingerprint to identify the specific firearm used in a shooting. A comprehensive ballistic identification system would connect a bullet or cartridge case recovered at a crime scene directly to the make, model and serial number of the gun from which that bullet or cartridge case was fired. In effect, comprehensive ballistic identification would allow police to trace a gun even before they recover that gun.
A confirmed link between a specific firearm and a bullet or cartridge case recovered from a crime scene constitutes a valuable lead, because investigators can then connect the firearm to its first purchaser, who may become either a suspect or a source of information helpful to the investigation.
A technology called "microstamping" is now making comprehensive ballistic identification a reality. Microstamping technology utilizes lasers to make microscopic engravings on the breech face and firing pin of a gun. As the gun is fired, a code identifying the weapon's serial number is stamped onto the cartridge. The technology promises to greatly aid law enforcement officials in investigating homicides and other gun crimes.
On October 13, 2007, California Governor Arnold Schwarzenegger made history by signing a first-of-its-kind microstamping bill into law.  The District of Columbia enacted a similar microstamping law in January 2009. Several other states, and the U.S. Congress, are now considering microstamping legislation.