"The Shooter Had a Powerful Rifle and High-Capacity Magazines The gunman was armed with an AR-15-type semiautomatic rifle and a 9 millimeter handgun, Chief Mina said. AR-15s, which were first developed for the military and used extensively in the Vietnam War, are widely owned by assault-rifle enthusiasts. The rifle, which can rapidly fire multiple high-velocity rounds, has been used in a number of mass shootings, including those in Aurora, Colo.; Newtown, Conn.; and San Bernardino, Calif."