I think that the FBI set him up for a weapon sale to terrorists, and the SHTF, when security guard showed up, and the terrorists got the weapons, and shot the people....FBI Cover up for their part in doing this nonsense, imho.
That might be too simple, but something went wrong, and many died. There were several people from Saudi Arabia arrested that week, and one Prince was in that hotel per an article I read...something was going on that is classified.
I’m not aware of the details you have suggested.
However, considering the lack of information regarding a motive in this case, I’ve been more and more convinced that the Shooter was an FBI “target”. Someone that they could hold out/up as a success story in their effort to paint an average White American Gun enthusiast as a Domestic Terrorist.
They wound him up and lost control.