“If the shooter clearly turned his rifle on the officer beginning to climb onto the roof, then wouldn’t that be sufficient justification for the police sniper to take him down at that instant?”
That’s assuming the counter sniper team can see the officer.
“That’s assuming the counter sniper team can see the officer.”
True. And apparently the officer just popped his head over the parapet and immediately dropped back down when the rifle was turned on him. He wasn’t standing on the roof fully visible to the CST.
But wouldn’t the CST have seen the assassin turn the rifle toward another target?