I saw your post in the contradictions thread, DeadCat. Thank you!
I'm wondering if perhaps there were a couple of cops (on or off-duty) as security on hand prior to the movie starting, to keep the line orderly. Then maybe once the movie began, the theater manager figuring everything was under control and told them they might as well take off until the movie let out?
If they were on-duty cops, I feel pretty sure they would've left on their own once the movies got started, to patrol other areas.
JH must be crazy (j/k) because there's no way he could've known there would be no armed security inside the theater for that highly anticipated midnight opening! Well, on 2nd thought, I guess there's always a way.
All the above is hypothetical only. I hadn't heard or read this anywhere. Just thinking outloud, and posting as I think.