"The mass murder last week at the Pittsburgh Synagogue has something in common with the deadliest massacres: the AR-15 semi-automatic rifle. Variations of the AR-15 were used to kill at a Texas church, a Las Vegas concert, Marjorie Stoneman Douglas High School in Florida and Sandy Hook Elementary School. The AR-15 style rifle is the most popular rifle in America. There are well over 11 million, and they are rarely used in crime. Handguns kill far more people, but the AR-15 is the choice of our worst mass murderers. AR-15 ammunition travels up to three times the speed of sound."