The couple of cell phone videos I have heard one was clearly just the sound of firing. Another cell phone you could hear the snap of projectiles and then the pop from the weapon. They did not sound like controlled bursts, and if nothing was belt fed, some drum type mag must have been present as I heard burst in excess of twenty or thirty rounds. From his perch in the hotel he delivered plunging fire into a densely packed crowd 350-400 meters away for nearly 20 minutes by some accounts. At least one account states that the SWAT team was able to locate his room because the firing set off the smoke alarm. I would wager not a handful of those under fire had the faintest clue of where the fire was even coming from.
As far as bringing stuff in luggage, a guitar case or gig bag will easily accommodate a couple of full size rifles. Housekeeping had been in and out of his room since he had checked in so his weapons was likely not at stack arms in the middle of the room. That the clown had apparently been in the room since Thursday last, and chosen a corner with a clear view of the concert area suggests to me it was not a spur of the moment decision. Whether his motivation was somehow political or simply a desire to be more infamous than the last dickwad to shoot up a bunch of innocent people will be difficult to determine absent a note or some kind of manifesto. Maybe the police will find something in his home or on his computer.