Is the shooter an officer? To me it looks like the shooter may be the guy dressed in black in the corner of the doorway, or did the shot come from the other side of the door? Muzzle flash would indicate that the end of the barrel was just behind the head of the red hat guy. He might be police, or might be provocateur, hard to tell, maybe some more photos/footage from a different angle might shed more light. Slowing the video down to half speed, there could also be a figure retreating directly after the shot on the other side of the glass, so not entirely sure who the shooter would be. Perhaps there is security camera footage for that area? Although, the chances of them being "broken" are pretty high.