They KNEW he was scoping out the site several days before attack?
So… If they knew he was scoping out the area a few days ahead
When he showed up on Saturday, why didn’t they stop them?
Especially with rangefinder in his hand and facial ID??
They probably helped him.
"Hey, Tommy, why don't you take that building over there. The slope on the roof is a little too much for us to handle."
I doubt that they knew he was scouting the area before the event actually happened. I’m assuming that they are guessing this from cell-tower positioning information that they are looking at. They can, in hindsight, say where he was prior to the event.
Almost as if they were in on it.