This cannot be a true story. The officer would have alerted other officers and the SS.
The eyewitness who filmed the shooter on the roof was just on Fox. He said the policeman climbed the side of the building (No Ladder) and was holding on from the roof and he just fell down to the ground after the perp aimed at him. He made no mention of a ladder and clearly said the cop climbed the side of the building.
All: The cop couldn’t shoot him because he was holding on to the roof with both hands, then he let go and dropped to the ground.