I think it's best to discount the PM for who is innocent or not. DK could've put down any names, all innocent, all mafia or mixed. It turns out one was innocent and maybe more if the cop has investigated any of them but that doesn't mean we should pay attention to the PM. It is just a tactic to sway us as we have to realise that we can't ever find out if they are all innocent unless the real cop tells us. Even if he did we can't know if one of them isn't the Godfather.