"On July 20, 2012, a mass murderer killed 12 and wounded 58 others at a movie theater in Aurora, Colo., using a Smith & Wesson M&P15. On Dec. 12, 2012, another mass murderer killed 20 children and six adults at Sandy Hook Elementary in Newtown, Conn., using his mother's Bushmaster XM15-E2S. The letter and number suffixes belie a simple truth -- the guts of both guns look just like an M-16 or, as it is known for civilian use, an AR-15. OK, the M-16 can fire in fully automatic mode but otherwise, the same. In Orlando just this month, it was a similar type of semiautomatic assault weapon, a Sig Sauer MCX, that helped claim 49 lives."