What Jace said, it's true. Mafia can agree to vote one of their allies, but it could also be that the King chose a mafia guy, who knows. Only those who are part of the King's court know what happens and if they are trusting each other, i can only hope that in that group there are only townies.
Also Alaris has right, it's bit risky to kill one of King's court without have suspicious or proof.