I would like to add to this, stuff such as violent movies, music, shows etc really should not be used as an excuse. That stuff is in every country, we got it all down here in AUS and UK, compare the murder rates of London to any major city in the US.
Clearly guns are responsible for most of this, hate that argument that bad guys would just use knives etc anyway. You take guns out of the US (make it extremely hard to get them) the murder rates will fall, accidental shootings would also fall. Make it near impossible for these nut jobs who do these school shootings to get guns. A crazed guy over here would find it near impossible to get hold of a gun no matter how desperate he was. Hell you can't even get bb Guns over here LOL.