Again, check your sources. Lanza left a
shotgun in his car, not his AR15.
http://www.cnn.com/2012/12/18/us/connecticut-lanza-guns/index.html
The primary weapon used in the attack was a
"Bushmaster AR-15 assault-type weapon," said Connecticut State Police Lt. Paul Vance. The rifle is a Bushmaster version of a widely made AR-15, the civilian version of the M-16 rifle used by the U.S. military. The original M-16 patent ran out years ago, and now the AR-15 is manufactured by several gunmakers. Unlike the military version, the AR-15 is a semiautomatic, firing one bullet per squeeze of the trigger. But like the M-16, ammunition is loaded through a magazine. In the school shooting, police say Lanza's rifle used numerous 30-round magazines.