>>but the pitch of the roof Crooks was on prevented them from seeing the 20-year-old until he moved to the peak and fired his weapon
>HA! People saw him from the EFFING ground!
Yup. Also, the use of the reverse slope is a basic tactic. The Duke of Wellington did this all the time (notably at the Battle of Waterloo). Find a slope where you can’t be seen but where you can quickly pop up and fire. This is pretty basic stuff. I would think a security team would specifically look for such hiding places. Ideal for snipers. They should have known about that vulnerability, and when people on the ground starting yelling about seeing someone, they should have been right on top of it.
It’s called “defilade”. Daniel Morgan used it at Cowpens.
Stonewall Jackson used it Bull Run. Israeli Armor used it in the Golan Heights.