Agent’s rifle was already locked on the line of fire. He jumped when the shooter’s first shot rang out, rifle barrel went up, came straight down and the agent fired. No way to acquire the target that fast in a scope unless his rifle was already as I described above.
There were two agents with their rifles trained on the apparent assassin. I figured the guy kneeling was assisting with spotting, the guy laying down was the actual triggerman. The spotter’s seemingly surprised reaction allowed his gun to flop, but he returned the gun to its resting position and fired possibly thinking the rifle’s orientation was intact. The other sniper creeped backwards after shooting which I’m guessing is a trained self-preservation maneuver.