Stop being a jerk. He "thinks" he can return back all the way to where the shotgun is but isn't sure. There are some points in the game where you can't back track. I don't know the answer, but I believe you can back track. I had to back track from the Communications Officer to the Sniper Rifle and come back to kill him at the very least. Unless someone else responds, you'll have to try it yourself. If you can leave the round room with the huge clock and go a room or two towards the end of the ship, then you should be able to. Usually this game blocks you right away if it doesn't want you back tracking. I hate it when people just post to be stupid rather than be helpful.