Actually, the only case I know off hand is Columbine. Both boys did have depression.
And how are you to know the status of their mental health? Did you know any of these people? Do you know anything of psychology, especially to the degree to diagnose someone? No.
I, however, do know a little something about psychology. These things just don't pop out of nowhere. Usually there is genetic factors, but not in all cases. But in order for most psychotic breaks to occur, there is usually a predisposition(er, sp?), and then the video game can trigger the psychosis.
Again, video games can trigger psychosis, but not cause. There is a difference.