I find that extremely odd. There would be some sort of light from the firing position, especially from a machine gun.
Not if the guy backed up into the room a bit. If his gun was mounted on a tripod, it would not be seen unless he stuck the barrel outside the window. Also, he probably had a flash suppressor on the gun.
Pretty sure no tripod because according to the “official” story, he had to go back and forth between two windows, firing nearly continuously if you listen to the audio.