I had read that that was the ladder that was put up and used by the police “after the fact” - that is, after the shooting was done. But one might ask, why would they put it in a semi-hidden location like that, behind those tall evergreens?
Answer - my thought is that the ladder WAS used by the shooter and was pre-staged. Since the SS didn’t fly any drones that day apparently, nobody would have spotted the ladder ahead of time.
Inside job.
That ladder was used by LLEO after the shooting, not the shooter.