How about we don't blame the media, or movies, or video games, or gun laws, or his family, or society, or even his alleged mental illness? How about we blame the crazy asshole himself?
Shifting the blame often ends up sounding an awful lot like making excuses, and I don't think people really want to do that. Not for this fucker.
I know that people want to make sense of it all, to try to understand why he did what he did, but I think that Occam's razor applies in this case. This guy was a monster. Period. What he did was horrific. But he did it.
Blame him. There are no so-called mitigating circumstances that could ever come close to explaining the killing of those innocent children. So don't even try.