I would agree that you could try and probably succeed to use violent games/movies in a way that would fuck with the child's psychology to make him violent. But that would be an abuse and not the normal protocol that goes along with playing games and watching movies. I would not say that no one never did anything violent inspired by video games, because there are clearly many stories that shows that. However it does not mean that without games something bad wouldn't' have happened. If you would have to bet, what would you say is more probable?
1. Violent video games makes people more violent in real life.
2. Violent video games gives people environment to spill their rage thus making them less violent in real life.
To my knowledge there is just no studies to show any link to violent behavior and playing violent video games. And to me this simple approach - violence in games makes violence in people is just so dumb.