Well, it's a tricky move. The Mafia protects a completely innocent player, then during the day, they vote to execute him. Of course, he doesn't get executed, and that's it! 100% Mafia win.
Added 1 minute later
I don't understand why the Commissioner would reveal himself when the Doctor is dead. It's an easy target for the Mafia.
Also, if the Oracle is lying, the real Commissioner will punish her.

