Reading up on American mass shootings, it occurs to me that "crazy people doing crazy things" seems to be the explanation for most of them. Seldom is religion or politics a factor.
Sorry, I don’t buy the “crazy” motive. Not this time. Too much pre-planning to claim this guy had a psychotic break and no one coming forward to say they saw any change in his recent behavior. A person that just goes off the deep end and starts killing people won’t take days to prepare his arsenal, a planned way to escape, or spend 8 hours before his attack quietly playing video poker. If you want to define a cold-blooded sociopath as crazy - yeah, I can buy that, but he was not the “just suddenly snapped” kind of crazy that some people are trying to claim.
When we don’t understand the motives for an evil action we call it insane, but to the evil doer his motives seem perfectly reasonable.