I don't know if you could classify him as insane. Disturbed, yes, but I don't think an insane person would have the wherewithall to systematically stock weapons, booby-trap his apartment to create a possible diversion
(and cause more collateral damage in the process), enter/exit an emergency exit in close proximity to his car, arm himself to the teeth, protect every square inch of his body, and spray the audience with bullets at the exact moment there's a shooting scene on the screen. He had to meticulously lay all this out to pull off a stunt like this. This could not have been some random act/snap.
It was hard to read his body language at times during his court appearance- is he insane or trying to get you to believe he is? If he was crying, and showed the slightest degree of remorse, I'm not sure if that would fit the profile of insanity. (Temporary, maybe, some lawyer might argue).
If he is found not to be insane, and does get sentenced to prison, he's going to be such a big target. Just like with Jeffrey Dahmer, somebody in prison will want to be famous for wasting him.
I'm sure a lot of people in this country would love to exact some kind of revenge on him. But no matter what his fate may be, it won't bring the twelve victims back, nor will it bring closure to the victims' families any faster.
(Rhetorical question time): so where do we go from here?