At this moment in time, it's beginning to seem that maybe
a) The shooting and death may have been faked with a blood pack and blood tube used- Hollywood style... Because there's no other reasonable explanation for the moving dot.
b) The fan under the chair actually may have been a speaker to send out noise simulating a rifle shot.
c) The man in the turquoise shirt next to the white-cap man may have had a click switch to trigger the simulated shooting and the noise. Hand signals by the two guys who gave them may have been to the crisis actor on the roof to get moving and disappear from view. And to the two fake suspects who behaved oddly to distract and confuse police.