I'm not really sure what kind of planning you think is involved in carrying bags into a hotel room. In a hotel like that, hundreds if not thousands of people do it every day, bags of all shapes and sizes. They're not going to care one whit if a guy lugs a few duffels to his room from his car, are they?
In other words, people seem to think it's a lot more difficult to bring luggage to your room than it really is. Admittedly, in Las Vegas hotels there's not always that straight shot from car->room like you'd see nearly anywhere else. You're usually walking past the front desk, through the gaming room, to the elevators, but so what. You get a cart, load it up, and off you go.
Anyone who thinks hotels are going to start searching bags of guests after those, or wonder why they weren't already, needs to stay at home and never go outside, because that kind of thinking is weird and wrong and should never happen. LOL
So maybe you think the hotel would notice some suspiciously long parcels... rifles can be broken down. I imagine I could break down some ARs into the upper/lower and fit several no problem into a standard 30-33" tall rolling suitcase, with room for a couple thousands rounds of ammo. It'd be heavy but... rolling suitcase.
I concede the point about getting the guns into his room, but I stand by my other point about premeditation. The lunatic planned this.