Seems like your rogue has brought trouble on himself making off with other people's items. The ranger was rather rash in going after the item, but if you're the DM I'd sit down with the rogue and ranger's players and see if they can't come up with some more constructive solutions to this problem. The whole idea that the rogue has to take revenge because he's a rogue is silly. If players continue to take it too seriously then I suggest some time off from the game for them.