Watch The History of Criminalistics. Ballistics

Just like there are no two identical fingerprints there are no two identical guns. If a bullet casing is found at the scene, the experts can trace it to the gun it was fired from. The ballistic fingerprinting technique was developed in the 1920s. In 1929 this very method helped bring to justice one of Al Capone's gunmen and marked the beginning of the end of Capone's career.