No night one kill was one of two things. Doctor protection or mafia didn't make a move to throw a wrench into town investigators and the doctor.

For me the way the role was claimed was the damning evidence. It was almost a set response to if a role claim came out with evidence against them. By me insinuating my claim on Mitsuru it set off the chain reaction to throw one mafia under the bus koromaru in order for a mafia win end game. I have seen the tactic used before with great success for a mafia win.