Several people saw Crookes on the roof with a rifle and told police about it but nobody was too concerned and did not inform others in the area. That’s a setup by the police.
There is a video from behind Trump showing that anyone in the inner circle of protection could see Crooks moving on the rooftop. There is no way that every agent missed that unless they were all incompetent.
Bongino does a great breakdown of this.
Just incompetence.