So You will need X amount of cobwebs, X times 4 amount of obsidian or some other block, a few signs and glowstone. Just find out where he logged off at, build a X block deep hole straight down, with X times 4 block surrounding the hole. Now as you are digging down the sides of the hole, place cobwebs for every block. Then using the signs you can like make a revenge story or something. Illuminate the signs with the glowstone. The cobwebs will make his descent a slow one, and chances are he wont have a diamond pick. (HENCE OBSIDIAN) If you want, you can put lava at the bottom, but I would not. Then, destroy his bed, so he has to go to default spawn if he /kills himself. If you are extra spiteful put the same trap under the spawn point. Then booby trap his base (if you can find it) with a pressure plate and TnT. You would have to warn good people about the trap so you must make sure their spawn points are safe first. If you can You and Agent can set up sort of like a watch