On February 14, 1929 (aka Valentines Day), seven gang members were slain in what became known as the “St. Valentine’s Day Massacre” in Chicago, Illinois.
Four men dressed as cops storm gangster Bugs Moran’s headquarters on Chicago’s North Clark Street, line up seven of Moran’s gang members (Adam Heyer, Frank Gusenberg, Pete Gusenberg, John May, Al Weinshank, and James Clark, as well as a visitor, Dr. Reinhardt H. Schwimmer) against a wall, and shoot them to death. The St. Valentine’s Day Massacre, as it is generally known, was the end of a gang battle between Al Capone and Bugs Moran.
The police department suspected it was set up by Chicago’s legendary gang leader Al Capone. Calvin Goddard’s expertise was sought by the investigators. He published a summary of his findings in the first issue of the American Journal of Police Science in 1930. Given the established circumstances surrounding the shootings, the mere discovery of the shells in the garage was sufficient evidence that they were fired with automatic weapons. A close examination of the rifling markings left on these bullets revealed that they all bore the imprint of a barrel rifled with six grooves inclined to the right. All of the bullets extracted from the bodies were.45 automatic pistol type, identical in caliber, type, make, and vintage to those discovered on the garage floor. He deduced that the killers used Thompson submachine guns. Fred Burke, one of Al Capone’s henchmen, was arrested in December 1929 in St. Joseph, Michigan, in connection with the murder of a police officer. At his home, police discovered two Thompsons and a stash of .45 caliber ammunition. Goddard matched the firearms and ammo found during the Chicago massacre, proving that Capone was responsible for the shootings. Burke was found guilty and sentenced to prison.
Reference: Calvin Goddard, “The Valentine Day Massacre: A Study in Ammunition-Tracing,” American Journal of Police Science, January-February, 1930. http://www.firearmsid.com/ Feature%20Articles/stvalentine/index.html