There are many buildings in Vegas.. could be an echo.
Could be an echo. Correct.
Daily Mail has some graphic photos.
There are no other towers off of which echos can happen. Luxor is the closest tower, but it is a pyramid, so sounds wouldn’t echo very cleanly from it towards the concert location. The other tower is west of Mandalay, away from both the shooter’s location and the concert location, so echos would not bounce off of that other tower.