There was already some dude who started the ball rolling. He didn't even get shot! His friend did, so HE is in therapy now for the trauma. He is suing the theater, Warner Bros. (For making violent movies....such as the one he just had to be the first to see), and who knows who else????
The thing is, there are now news reports that the police themselves were begging for more and more ambulances, and they weren't dispatched for 30 minutes.
Also, you have the supposed notebook the killer sent his professor, that sat in his mail slot at the university for a week, and it detailed his plan for killing.
So, now you have municipality, and state agencies you can zero in on.