It's only natural, in the wake of any random act of extreme violence, to look for an explanation: What caused this to happen? What can we do to prevent it from happening again?
While it's fair to ask these questions, the frustrating truth is that most of the time, we'll never know.
Not knowing, sadly, is not an acceptable answer. Instead, "the other" is blamed. When it comes to politicians and lobbyists, this "other" is anything the younger generations are into, that they themselves aren't. Thirty years ago it was rap and heavy metal. Thirty before that, it was rock and roll.
Today, the common scapegoat is video games, and blaming them is just as specious.