Question for you
@amynhop. Why would there be a cover up and to what purpose? I can see if you were killing a specific person or something like that, but honestly who would cover up shooting up a country music event?
I don't see anything that this guy did that I couldn't have done EASILY. 800 lbs of equipment. That's 8 trips back and forth to the car over several hours (less if you borrowed a dolly from the front desk). With the butt stocks for the AR-15s, they are already in a easily broken down into a couple of 2 ft sections. Use blankets or some type of cloth to wrap metal equipment for silence. So equipment ... no problem.
I don't see the glass as a problem either. You can buy glass cutters anywhere. Home Depot would do. A few good quality suction cups and some rope to put reverse tension on the glass and it falls backinto the room. The glass is REALLY thick... I'd suspect that he cut most of the way through then shattered it with a hammer.
Pouring high powered nearly full automatic rifle fire into a nearly solid mass of people from 300 yards away? Child's play for a .223 round AR-15. Especially if he had something to prop on.
So while I have no info one way or the other, I am a big Occam fan...