It might just be that murderous psychopaths like violent games, not that violent games make them murderous psychopaths.
It has to be society's fault.
There is no way murderous psychopaths just have fucked up brains.
There has to be something more than that. This didn't happen a few decades ago, and it still doesn't happen in other countries.
Another piece of the puzzle. In the article that I linked to and that scg posted a few pages ago there's an interesting commonality, online mass shooter admiration communities.
There's a weird side effect of the internet bringing everyone together. People have the option to hide from reality by finding like the only 10 other people on the planet that believe that same insane thing they do.