He didn't snap, he's always been like this. Mommy and daddy never told him "no", they never taught him that life has disappointments and he had to deal with them and take responsibility for his actions. They bought him everything he wanted, including guns, because they were too lazy or too stupid to actually raise their spawn to be a self sufficient productive member of society. There are millions of them out there; thankfully only a few will take their tantrum to this level.
Is this sarcasm or a real take? Sometimes I can't tell with you.. You don't want to blame genetics. You don't want to blame his upbringing/parental influence You don't want to blame guns You want to blame the water he drank and the food he ate?? That's one warped ass take on the whole thing. Unless of course you were being sarcastic, which again I am not sure.