From what I remember, the game uses clues to identify the Mafia, but it seems like they just include it for the sake of having it. More specifically: it's mainly to keep players occupied during the first few days. Usually, they figure it out within the first one or two game days... and then, either by intuition, by using the "ND" (no death) strategy, or by psychology, I vaguely remember how they correctly identify the Mafia.
