Sandy Hook, Virginia Tech, Aurora, Columbine, Isla Vista, San Bernandino, Orlando, Charleston Church, all have one thing in common. Small arms, every single one of these massacres was perpetrated with small arms fire, some of them used a combination of rifles, assault-rifles, shotguns, knives, and explosives but all of them had some form of small arm. In fact several of them (Virginia Tech, Isla Vista, and Charleston) only used small arms. @Eco ARs are scary, large, and powerful but they are a scapegoat by the media because they are exactly that; scary, large, and powerful. It is easier to send a message of doom across the news with an AR than a pistol.
I hate to use Australia as an example but hand-guns are the most difficult gun to procure legally. Fully-automatic rifles are flat out banned but not ARs are fully-automatic. The gun I mentioned earlier, the common Colt AR15 is only semi-automatic, firing in bursts. In fact I'm 95% sure that automatic assault rifles (military grade) aren't legal in the USA.
EDIT: I am correct, fully-automatic weapons have been banned since 1986.