Maybe there is a remote chance of wallhacking, however I beg to differ. I'm not a shabby shot with a rail myself. I am highly allert and I can hear people grabbing a heath or ammo near by. For the sake of argument given this situation: say there is a mega heath and I hear someone grab it, then I go to that area. Then I hear the player grab some ammo that is near by. Now, I know that he grabbed the 3 bullet boxes because that is the only ammo set of three located by the mega health, so I wait until I hear him grab the last box, then I estimate the time it takes comming out from
the ammo boxes to the enterance, judging by the speed a player runs, I take him out before he knew what hit  him. That is just using logical reasoning, mathematical estimation, not a wallhack. Just a thought I'd like to throw into the mix.

No, no, no... I didn't get any ideas what so ever. I know my communication skills suck.
That indeed is suspicious. I am not excluding that inquiry for the use of wallhacks, what I am trying to say is, that there is a small chance that perhaps the player is really that good, a next to impossible possiblity, and like I said, that was just an idea I threw in. A "what if" idea. I do belive he was using some kind of unauthorized aid, but as the question from the novel "The Time Machine" asks, What if?