It makes me wonder how the perp even knew that the roof was available at all. Are we to believe he was able to scope out the location when it was a police facility?
Also note the perp lived thirty five miles away—it is not as though he had local knowledge.
Had to be inside.
What are odds that a 20yo known nutcase decided to drive over 30 miles to an unfamiliar area, use a police staging area, with the one roof that “happened” not to be covered even SS considered it vulnerable before the event, and scale the building like Superman, turn and scare off one police officer (who was also scaling the building like Superman), and able to turn back around, and somehow manage to mesmerize the counter snipers for 2-3 minutes while he was getting in place, and shooting.
He either has super powers or this was totally an inside job.