Part of the strategy of not telling users of having PM contact is because it can create suspicion towards you. If anyone comes forward saying a cop contacted them then almost instantly people may either accuse the person of lying and being Mafia, or assume that the cop that contacted them was Mafia. This is perhaps best exemplified through DK's actions just before he was killed off. Even in the aftermath people began to accuse those who had said they had been contacted as Mafia. So really making such information public is akin to drawing a bullseye on your forehead.