heres the usual snopes, they say "no shooter on 4th floor" but its possible that the floor that the flashing light is coming from is a mainenance floor, which would mean someone who works for the building might have placed it there. it caused a lot of people to think that the shooting was coming from a lower floor (was the light placed there on purpose?)

> I haven't seen any flashes from Mandalay, but if it is coming from Mandalay there is a strobe light coming from one of those windows on the east side.

https://www.snopes.com/fact-check/second-gunman-shoot-fourth-floor-mandalay-bay/ https://archive.is/nhSM0

edit: youll notice they "debunk" a second shooter the classic snopes way: strawman. by the time this article came out pretty much everyone thought the shooting was coming from the north or north west, not two shooters at the hotel