I'm agreeing with Tuffty here.
Sure, if someone had gone nuts and really to kill some people, he would use any methods he could and there's no stopping him (Anyone could just just drive their 4WD into a uni and start running over anyone he/she sees and there's no way you can ban cars).
But potentially, it could be a spurt of the moment thing...for example, if a cleaner gets made fun of by some asshole students, he goes home feeling his pride was hurt, then he sees a shot-gun in his cupboard...I guess what I'm saying is that having proper gun laws may not stop all these shootings, but having them reduce some of these spurt of the moment stuff.