Maybe everyone on the security detail was afraid of heights.
The building behind also has 12 ft elevation above the shooter and a team should have been there as well
They might have accidentally discovered the was/were climbing a wall, with a gun and scooting across the roof below they might have put 2 and 2 together...
How did this guy even get a gun in the area and then scale a wall?
I looked. There is no ladder to that roof.
There might be to the intermediary of the 1st floor but, there is zero ladder to the rooftop of the second