With all due respect, that's an extremely volatile and unfounded accusation. Moderators are not the therapists of the world and are certainly not responsible for this kind of behavior.
Nothing on a single website can make a kid like this. Being isolated really helps. The core of this stupid, destructive impulse is way beyond anything perchance or a single website can do.

People shoot up schools because they want to be remembered and they want their rage to be legitimized. Short of reporting him if his IP is known, the best way to deal with this is just to ignore it. This is a desperate and pathetic act, and giving it attention just makes people like this feel successful at something.