All he had to do was look. He had been casing the building complex for several hours..
He had no way of knowing that nobody would come up on that roof and he knew counter snipers were in place.
People said they saw him and he had a gun yet nobody stopped him before he started shooting.
They had pictures of Crooks taken earlier where you could see his face. That dead guy on the roof did not look like Crooks.
Did he not look in the window where there were officers in a countersniper position? Did he just run past them while they lit a smoke, were they fellating each other?