When Adam Lanza entered Sandy Hook Elementary School on Friday, December 14, inexplicably bent on ending as many lives as possible, he was carrying a Bushmaster AR-15 assault rifle and several high-capacity magazines. Sadly, this isn’t the first time the country has had to deal with the aftermath of a horrific shooting spree, nor is it the first time we’ve encountered an AR-15 in this context: only days earlier, it was the weapon of choice for a shooting at an Oregon mall that killed two people.