As soon as you arrive at the spot where Reznov leads you to, wait for Amsel to come out. You could try shooting him a bit, but I would suggest you save some ammo.
Now as soon as he retreats in the car, kill his driver, and he'll start to sprint away. He is currently in sight with nothing to protect him. Now is the time to shoot him carefully. Make sure you don't miss because he is pretty fast!
Good Luck and I hope this guide helps :D