For the moment now I’ll give him the benefit of the doubt after watching closely.
The Sniper appears to be “glassing” (eyeballing something specific) to the left of where the shooter is. What that was could be important procedurally (vehicle? person? hot chick?) He most likely has the magnification dialed up to at or near maximum. The Field of view is tight at the shooters distance. It is VERY difficult to transfer from target A to B at that distance without removing your eyeball from the glass to look, or lowering the magnification to widen the field of view to transfer/find the new target.
I know this from shooting a scoped rifle sport (Field Target) at very small objects in a timed setting.
You can see him, probably at the cue of the second sniper/spotter or shouts of people, pull off what he is locked on, look to acquire a target, and physically move the rifle/tripod setup to a target that is to the right and lower.
It is the sniper to the right that appears to have had/made
aquisition and had the shot potential first (he has a rifle). I’d need to watch that in relation to the assassin fired shots because the order/timing of those shots are important in relation to how the roof team movements unfold.
I think that one of the roof team, probably #2 (right) had the assassin in view and possibly lined up before the incoming shots. #2 is probably the team member that made the kill, shooting the guy in the mouth and out the back of the base of his head/neck from the close up of the dead shooters head.
Scoped rifle under 200 yds at a 6 in target? The shooter sucked as bad as the overwatch did.