There were no cameras in the hallways, stairwells or elevators in the Mandalay and 22 other Hotels on the strip. Only 4 or 5 have those additional cameras.
FWIW, In the world of Smart devices, there are a multitude of devices recording all these events, which even the most skilled professionals usually omit.
Let's take a simple one.
HVAC systems. In most high rises and especially hotels, it isn't uncommon for the individual rooms to have thermostats, but they are usually on a network with numerous controls monitoring the systems.
For example, even if not reported, each room likely has three sensors: A door sensor, a thermocouple, and a motion detector.
The door sensor (door alarm) will likely detect when a person enters or leaves the room. This will set a conditional to monitor the motion detector. If no motion after a time counter elapses, then the HVAC system doesn't have to maintain the cool conditions for the vacant space.
When the door is opened again, the HVAC turns on and brings the room back to fine tuned conditions. Saves lots of money in energy costs and there is a litany of other programming for hotels to save energy costs. Count on that to be implemented in someplace like Mandalay Bay.
These systems typically are monitored over modems from each floor and at least each bldg for contracted HVAC maintenance. If somebody can access those codes, they can monitor who is coming in and out of every room in the building.
Cameras aren't necessary, but then again, if everybody has a cell phone, who needs cameras? Just scan who enters and exits the doorways and then activate their cellphone microphones/cameras, even for just a few shots. All IEEE 802.11 compliant.
Where are these reports being provided to the public? It isn't as though the younger generation isn't more in tune with this than we are....