I checked the wiki a bit and found a couple explanations:
http://wiki.mafiascum.net/index.php?title=Rolestopper
http://wiki.mafiascum.net/index.php?title=Roleblocker
http://wiki.mafiascum.net/index.php?title=Jailkeeper
So I really hope the Mafia doesn't have a rolestopper that doesn't prevent kills.
I still think TW has to go...
@R2V: I have a question for you: you claimed you're Luke, a watcher and you targetted Robert on the 1st night. What was the outcome as you didn't specifiy this before?