It looks like a metal roof. Having someone up there would be very loud to anyone inside the building.
Maybe they had the TV volume up very loud.
Their security earbuds were jammed tight into their ears.
Maybe that’s why that didn’t hear the guy that should never have been able to access the roof, on the roof.
“Having someone up there would be very loud to anyone inside the building.”
I give these guys a break on this as the shooter was crawling, not walking.