This is an old, old topic, but since it's come up, I'll throw my 2 cp in. I've always thought it odd that whenever something like this occurs (which is all too frequently), parents and the media are so quick to demonize videogames, yet this behavior has been around since the dawn of mankind itself. Violence in movies is so much more pervasive and visceral than anything you could possibly see in a game, yet movie scenes are very rarely cited as the source of antisocial behavior.
What's the difference? 'Experts' claim that it's the interactive component of games that causes kids to freak out somehow -- that somehow modeling violent behavior engenders a desire to commit similar acts in real life. Yet, if that were true, I'd have gone on a killing spree long ago.
I've been playing videogames since there have been videogames to play. Pong, sure, but also Space War. I've played very nearly every major console system, hundreds of coin-operated stand-ups, and too many LAN parties to count or comfortably remember. I've never even so much as gotten into a fistfight with someone. If videogames were really the pernicious influences they're commonly painted as being, surely I'd have gone off the deep end a long time ago.
No, the true culprit lies squarely in the fact that humans are blame-avoiding machines. No one wants to be held accountable for their actions, if found to have negative repercussions. 'The Devil made me do it' as an excuse, has been around forever. Look at how it works: a kid does something he knows he shouldn't, and when caught, indulges in blaming behavior. The parents, responsible for their child, engage in the same behavior. Guess from whom the child learned it?
I'm a parent myself, and I teach my son consequences, and that it's okay to make mistakes. It's not okay to duck blame to avoid punishment. What's critical is learning from mistakes to avoid repetition. This is the fault to be had in this scenario, not in any external source. Parents, if you want a good society, start at home with your own. And that's one to grow on.