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.

Is the parents fault and the background that made him take this path,mods can't babysit other people kids

The chat on my page isn't very busy, but even with a slow chat I don't always catch everything that happens there. I can't be online 24/7 to monitor it. This is a hobby, not my job. You also have to remember that "minor" means different things in different countries and there is no real age verification here. The "minor" you are referring to could very well have been an adult trolling or even law enforcement trying to attract a predator.

What, how is this the mod's fault??