For one. If the "overseers" really aren't the mafia, then why didn't the mafia kill them? What mafia member wouldn't want to take out a major pr the first night? The first logical conclusion is that they are in fact the mafia, so neither died, and the second that the mafia is trying to convince us that the first is true.
And for two, Iggy, one of these so-called overseers, gave such obvious clues that he was part of the mafia, and used the claim to save his skin. And even then he fumbled it. Role PMs are meant to be clear, if I'm not mistaken. How can you possibly misread one? He claimed vanilla town and then latched onto a suggestion of what his action could be.
If this really does turn out to be a ploy by the mafia, I'm going to be either laugh or cry because you all fell for such an obvious trick.