I think this game was partially to blame for the murder, I know that sounds silly but it is a violent game and studies show watching violence makes you violent, however, his parents bought him the game, his parents knew what it was about and his parents let him play it. He also took drugs and so on, so was obviously not in the most friendly of crowds (I'm not saying people who take drugs arn't friendly, I'm saying the people who sell them arn't).

So yes the game is partially to blame for teaching him effective ways of murder but it is also his own fault for being a psychopath and wanting to kill along with his parents fault for letting it happen.