... I'm not sure what I would do.
The best that you could under the circumstances.
I am having a hard time believing he acted alone.
If you think you are having a 1v1 in the Main Arena, your SA has failed you.
Who's going to run the metal detector, the 16 year old girl that usually collects the tickets? If they install metal detectors in movie theatres because of this I will never see a movie again purely out of spite.
What was there to detect? He went in unarmed. He then propped open an exit, went and retrieved his stuff from the parking lot, came back in the exit, then did his...deed. How would a metal detector detect anything at that exit? If anything the exit warning lights might have been ignored... or even disabled possibly.
"Hang him high in the street for all the people to see" We put down vicious dogs and there are other animals that may need to be put down also. Not saying it would have stopped this lunatic but maybe some quick justice will make others think twice. 10 years on death row and lawyers talking BS has made our current Death Penalty ineffective.
The number of wrongful executions would increase greatly if your idea of "quick justice" were implemented.