Case in point where Jonathan is cheating in Garry's Mod, Basewars.
For real though, you have no definite concrete evidence of the dude cheating. Unfortunately you got domed, sorry that happens. Just because someone is proficient in a game doesn't automatically mean they're cheating. I know everyone dog-piles on Jules for cheats, but if you'd take the time to check you'd see he comes up clean.
aren't you the guy you cant hit a single person with 3 60 round magazines? perhaps you aren't the most perfect judge when it comes to these things.