Whatever the state of mind of a potential killer, in order to commit mass urder on this scale he/she has to have access to a gun.

Everyone who owns a handgun, assault rifle, semi-automatic or automatic weapon is a potential murderer (I take the point about the need for shotguns if properly regulated - but even in the UK there are issues here as my son, a police firearms officer, will testify) - look at the statistics of shootings in different countries again, for fuck's sake. Anyway, I'd hate to meet any of you gun-totting, macho apologists when you were having a bad day. Grow a pair instead!