I need help killing zombies in black ops!?

Hay IV been playing a map on black ops zombies called "five" with my friends and we have been having trouble killing the Pentagon scientist theif. IV heard some rumors of how if u run away from him long enough he will drop a max ammo and disappear, or if you kill him he will give your gun back. But I have also heard is that he cannot be killed. Has any one ever killed him and what is the best way to kill him? Does he really give ur gun back and will he drop a max ammo?