That sound an awful lot like a simplified mafia game I used to follow years ago called "Playing Detective" (Adapted Translation), in fact, it sounds exactly like it, players could not change their names, avatars or sigs for the duration of the game, every turn the killer would leave "clues" to his identity, based on the player's sig, name and avatar, the "Detective"(cop) would gain an extra hint, the "Angel"(doctor) could protect people from being killed at night, and these were the only power roles.
I rather enjoyed it myself, it was a lot less sadistic than mafia is, at least, but I can see where people would fail to see the appeal after being exposed to actual mafia.