[quote name='seanr1221']So...I'm not sure I'm understanding what you're saying. Is the blame on him (and he was most likely not in a typical mental state), or the probable troubled environment surrounding him?[/quote]
Ultimately I blame him because he decided that was how he was going to deal with his problems. He made the decision to kill. He could've just killed himself, or took up drugs, or gotten help. That was the path he choose.
But of course it would be wrong to say he just did it out of nowhere. He obviously had problems through his life. His hatred towards everyone definitely points to him being "shunned" by his peers. Who knows what early traumas he had in the home, and even just his genetic predisposition. Yes, his environment (and possibly nature) was certainly a factor.
However, a LOT of people have negative past/present experiences (abuse, neglect, being picked on, chaos in the home). They make the choice how to deal with it. He, like the Columbine kids, went the extreme route.