Preface: I'm not sure how you guys record/upload/view demos and so I just recorded and put the video onto youtube.
Playername: The Fagger was playing on overgrown and doing quite well. This was not suspicious, what was suspicious was the fact that this player followed other players behind walls with his sights. I noticed when I got on the roof without anyone noticing and I was getting shot through it, and then it happened a second time as he followed me with his sights through the roof.

At 0:02 he immediately starts shooting at enemies that he cannot see such as through a roof, and then he immediately knows where one is across the map.
At 0:27 he knows an enemy is coming despite them not making noise and he is ready for them. It may have been luck, or radar, but I doubt both.
at 0:50 he is tracking enemies before they even appear in door ways. King of prefire.
at 1:03 he begins shooting at an enemy he cannot see at all. There was an enemy there, I accidentally cut the clip short but I have another 45 seconds.
at 1:21 he is tracking players through the bus.
at 1:48 he immediately starts firing, getting kills tracking enemies through crates, etc.
at 2:07 is the most obvious walling I've ever seen. In fact he runs out of ammo as he shoots an enemy behind a wall that he was not previously shooting at.
at 2:25 he is continuing his charade and that is where I decided to stop recording and upload the video. He then lost connection and did not rejoin the server so far.