Mandalay Bay and MGM are in deep kimchi on this one, not only if this proves true that they didn't call police right away, but also for not noticing some guy bringing all those guns and ammo into his room.  And he had access to the service elevator (which is what I read in a different story)?  That place has cameras, security, workers, ... every where and NO ONE saw anything that appeared suspicious?  And how does a guy fire 200 rounds inside the hotel and it not draw all sorts of attention from other guests and staff?