It was dark out(midnight), he parked close to an outside exit(all theaters have them) and kicked the door in. In all likelyhood he wasn’t trying to conceal them at all.
I think most of you are assuming that he walked in through the front door past a shit ton of people and walked down a hallway to the theater stage, which is not the case. He came in through an outside access door/fire escape right from the parking lot.