I read one report that it was a three round burst model. IF this is true, then this was not an AR15 but a US FEDERAL GOVERNMENT M4 or M16A2 modified for three round burst fire... as most all Military and Federal agency Stoner weapons are modified to operate. Makes one say hmmmmmmmmmmmmmmm!
I suspect it was an M4 or M16, taken from one of the guards or LEO, and not an AR-15. Same with 9mm semi-auto pistol. I read he only had a 12ga to start with but ‘gathered’ more weapons along the way, as he killed others. But that doesn’t fit the libs’ agenda. They want it to be an AR-15.