Some very confusing things about the shooting. The distance from that 32nd floor hotel window to the middle of the concert grounds was about 1,700 feet or almost 600 yards and according to multiple reports many bullets went through the bodies. Also from listening to recordings the rifle(s) had to be full auto for such a rate of fire. So, it had to be a quite powerful long range capable caliber in addition to the fact not too many 64 year old average men could possibly have enough control over said weapon type, rate of fire and caliber to even be able to hit the area very many times from that distance. That is pretty much military sniper level shooting.
Not impossible at all but sure enough difficult.