Many accounts from law enforcement and those in the crowd, say that he first opened fire near the stage causing panicked attendees to run away towards the exit. He then shifted fire to the 2nd window at a different angle and shot at those near the exit. One gunman, two angles.
I don't think there was a second gunman at all, and it makes sense that he may have fired from both positions.
It's the two angles that I'm somewhat questioning. From that high up and that far away, moving the nozzle 6 inches to your left from either position would probably be enough to focus fire from the front of the crowd to the rear.
The point is that before leaping into second shooters scenario’s that can avoid detection from cameras in the casino, who leave no forensic evidence behind and a conspiracy by local police and hotel employees to hide the evidence of two shooters that there may be reasons more simply explained.
A possible second theory that I have is air flow. With two windows open he could reduce the smoke in the room.
There are any number of simple reasons that avoid the necessity of two shooters.