In preparation for what would become the deadliest mass shooting in American history, Omar Mateen bought an .223 caliber AR-15-style assault rifle and a 9mm semiautomatic pistol, law enforcement officials said. The shooters in December's San Bernardino terror attack also used AR-15-style rifles. So did the shooters in the 2012 attacks at a movie theater in Aurora, Colorado, and an elementary school in Newtown, Connecticut. Critics call AR-15-style rifles the weapon of... (GunPolicy.org)