I would agree that the Manaan trial should have had endless hordes of level 20 guys (and possibly with damage resistance) coming at you to detain you.
Realistically, I don't think it would be possible to get out of Manaan after you admit to killing the Sith for fun....but rather than just cutting to your execution, set up an impossible fight where you get knocked unconscious, captured, and executed.
However, having said all that, you were likely already incapacitated in some form when you were on trial. They probably should make this endless horde come when you attempt to resist capture. It'll give the illusion of doing your own thing, but still limit the player down an easier to maintain path.