I've listened to the reports and the Sheriff's explination. Here is what I have pieced togeather, and I feel this is as accurate as has been told by everyone in the know. Not the Media.
The guy showed up bought a ticket and went inside. (My openion, While inside he put a piece of tape across the bolt on the exit door lock. or jambed something in the door to hold it from locking). Then it is reported he went back outside. Then he came through the Exit door wearing Body Armor, a throat protector, groin protector, and a ballistic helmet. The only vulnarable spot was his face.
Any CCW folks that had tried to shoot him would not have been able to see all the body armor. Anyone shooting him center mass as trained would have made themselfes a target. A pistol bullet hitting that armor would have hurt him, about like getting hit by a hammer, but doubtful it would have knocked him down, especially since most CCWs carry 9MM or smaller. Few carry .45s.
The guy threw in two bombs of either tear gas or smoke. Then he fired into the ceiling like the Joker did in the last Batman Movie. After that he started shooting at people with the shot gun. When the shotgun was empty he started using the AR. he walked up the aisle, shooting people hiding behind seats. Then he left the theater and headed for his car. Since the police was already present one of them seen him fleeying out the exit headed to his car.
Now he expected someone to have already opened his apartment door, so he told the police about the booby traps at his apartment. At midnight when he walked into the theater, a timmer started music blearing at his apartment. He had left the door unlocked. A neighbor had gone to the apartment and knocked on his door. She checked the door knob, and found the door unlocked. She pushed the door open just a little and yelled. No one answered, she thought about opening the door farther, but thought this is not right, so she pulled the door back closed and went back down stairs to her apartment.
If she had gone into the apartment, she would have probably been blown up, or severly burned. Along with anyone else in surrounding apartments.
I have to say this is a rumer and unconfirmed. Word going around in Biological Academia, he failed a test that would have gotten him washed him out of the Biology PHD he was going to school for, that is why he is reported to have dropped out. I think we may hear more about this later.