The earliest citation in the Oxford English Dictionary for the American usage of the term 'G-man' was in 1930, from a biography of Al Capone by F. D. Pasley. The nickname may have originated during the September 1933 arrest of the gangster George "Machine Gun" Kelly by agents of the Bureau of Investigation (BOI), a forerunner of the FBI. Finding himself unarmed, Kelly supposedly shouted, "Don't shoot, G-men!