I'm sorry if this seems insensitive. But I don't think this is a proper diagnosis, I believe this is just another form of "targeting violent video games" so law enforcement has somewhere to point fingers rather then at the shooter himself. I haven't been keeping up with this horrific story since it happened but I will say that they have it wrong, and need to investigate a different direction. Violent video games are not the cause of this incident, whether you want to believe it or not.
Having finished ME3 recently, I can say with utmost confidence that I noticed a sharp decline in "good". ME2 was far more story driven and delivered excellence in nearly all aspects, aside from a boring minigame, from beginning to end. ME3 was fun, but lacked the storytelling that I've come to love and expect from Bioware games, Ignoring the reviews I'd say ME3 sort of "phoned it in" giving players a large selection of weapons and prettier combat in lieu of focused RPG elements that would have, and could have, made ME3 a far better game.
Xeo_Fury's comments