Whenever something violent happens in America someone, somewhere blames some sort of entertainment media.
"The did it because they listened to violent music/played violent games/watched violent films."
Some people might say that the two things aren't connected - I'm not one of those people. There might be a connection between playing 18+ hours of very graphic, violent video games and committing mass murder. And since he would have been playing the games for years before committing the crime, the games caused it - right?
Here we have the failed logic that if A and B are connected, and A occurs before B, then A caused B.
But there could be a 3rd factor that caused both A and B to happen. That third factor is the real connection between the 2 events.
Take our mass murderer for example. He really got off on violence, he couldn't get enough of it so he started playing video games, eventually he was playing for 18hours a day. He just couldn't get enough - he was more interested in the violence at this point than sleeping, eating or social interaction. He was playing so much that he was getting bored of killing the same people in the same games over and over again. It just wasn't enough anymore - he needed the real thing. So he loaded some guns and left his house. The graphics in the real world are so much better.
His obsession for these violent video games was really only an indicator of his own infatuation with death and gore. It is this that caused him to go out and kill people - not the games.