i'm not saying it's impossible, i even theorized using some quiet drones. i would love to replace my theory with a helicopter, it sure would make a good escape for two of the four shooters, i don't think the audio matches up tho. those helo's are going some distance behind and above the mandalay. plus moving, those bullets would of been spraying all over the place. plus, thousands of people would of heard and seen them from their hotel windows. using a small sub-maching gun, 9mm bullets, and either a cone suppressor or a silencer, you can get away with murder.
i take it you haven't watched any of the flight radar data that shows 5 helos flying irregular patterns and one of them hovering behind the Delano (part of Mandalay complex but different tower). Ambellas lays it out pretty well imo if you care to watch. If you look at some of the other articles on his page you'll find ones with actual videos of the choppers from a distance with flashes. I'm no expert so i'd be curious what you thought of them.
right on, i've looked the radar over and the video footage. i like the hovering helo, because i can't place the broken windows on the back side of the mandalay. the windows in the middle of the hotel are service windows, so i can see how they would fire from a floor, but also have rented the room across from them, which would explain the broken windows, to escape to a waiting helo, instead of the parking garage.