Yeah, he has ally, he is able to find if someone is a member of the blue dragon or not. Be because the mastermind may or will listen to the king, no one will whisper anything to the king. which make his job very difficult.

You have 15 suspects in front of you and only 5 are evils. your chances of success are 33%. But we must lower this number because some evils will appear as bd members for various reason.