I don't see that necessary to describe what we see/hear so far.
Shooter is crawling to the crest. He should expect that the SS sniper team and spotters are looking at the roof crests, so he just needs to peep his scope over.
For the SS sniper team they may have the report, they might have the sight picture, but they can't just shoot on that civilian relayed report if it might be some freelance photog with a big lens laying on the roof.
Shooter shoots 3 times and then SS sniper team responds (could be spotter shooting too, could even be another team. We know what we've seen through a few straws.
Last shot might have been a final shot to 'make sure' by the SS sniper team, or LEO that finally got to the roof.
From what we've seen so far I'd put my money on a single guy acting alone.