I don't have any demos or screenshots, but if you check the Zombie Mod SourceTV for 7/12/11 at 9:40pm-9:45pm, I'm pretty sure you can see that the player "penquin" is using some sort of speed hack at the least.

This is his Steam ID:
STEAM_0:1:33323825

Just a side note to strengthen my case, I googled that ID, and it appears to me that this isn't the first offense this player has made

Thanks for any help!