I have been here before, seeing killers connected to computer games. Anders Behring Breivik played World of Warcraft. I do however think his more than 1000 pages long manifest, describing a process that started 9 years ago with the goal to become a European hero, is a lot more important than gaming.
It appears that he fits the FBI profiles of violent shooters, where they are interested in the violence, not the game.
Don't make the mistake of reducing this to "mad maniacal gamer" and claim the world will be a better place if the games are removed. Don't blame anything or anyone but the man who decided he had the right to take lives.