We cannot stop every act of senseless violence. We cannot know every evil that lurks in troubled minds. But if we can prevent even one tragedy like this, save even one life, spare other families what these families are going through, surely we've got an obligation to try.
Human law cannot punish or forbid all evil, since while doing away with evils it would do away with many good things, which would hinder the advance of the common good.
The first prison I ever saw had inscribed on it CEASE TO DO EVIL: LEARN TO DO WELL; but as the inscription was on the outside, the prisoners could not read it.