He would also use World of Warcraft to enter into a social isolation. He found people accepting if he told them he was "raiding a dungeon," leaving him time to both play and plot out his devastation. Players who were part of his online guild or joined in for questing suspected nothing. Some were friends for years, claiming he was, "an overall nice guy."
It's hard to tell what role, if any, games have to play in this tragedy. On more local soil, the "video games defense" has been thrown out, lawyers pushing it more or less to seek lighter sentences. Breivik, on the other hand, clearly knew what he was doing, in his mind his country being taken over by the Muslim religion. Call of Duty Modern Warfare being what it is, a fight taking place within certain current conflicts, certainly suited his own warped mindset.
Some type of direct blame is always a stretch, people seeking answers without resorting to logic. Breivik's case opens the door for religious fundamentalism, racism, drastically absurd patriotism, and of course video games as possible contributions. At the end of the day, people subscribe to all of those things, and yet don't see fit to shoot over 80 innocent people. Breivik is crazy and always will be. That's the only simple explanation.