I don't want to engage in conspiracy theories but I agree with...

I don't want to engage in conspiracy theories but I agree with you.
The whole purpose of SS snipers in elevated positions is to have what is called overwatch.
The whole purpose of their position is to ensure no threats exist, from particularly rooftops and elevated positions as well as at ground level.
How they failed to observe the gunman is actually beyond my recognition.
But where I agree with you is that they do appear to have their sights on something in the very near vacinity to where the shooter was located.
Even potentially more disturbing is that they even appear to then disengage from their sights moments before the shots ring out. Before going back to their sights and then neutralizing the gunman with quick successive shots. Related to that they also don't appear to have to alter their site picture by rotating their rifles before firing, suggesting their sights were already on target.
Now admittedly my last point is very dubious given the angle the footage is taken from, but it's all very unusual.
I can guarantee you any person with military experience or policing or personal security knowledge would agree their behaviour on the rooftop was highly unusual.
I won't go down the rabbit hole on that but at the very least it was a massive failure from the oversight sniper positions.
Their purpose is to identify and neutralise any threat ( before) anything occurs, not react after the fact.