I don't believe Koshiatar is the real cop, that was just too random and suspicious. I don't think the real cop should come out and reveal themselves either like cl_out's saying. They should investigate first and find out what's going on. Sure the doctor can protect the cop if he roleclaims, but that just gives an advantage to the mafia because they'll know who the doctor is protecting and can go after everyone else and know they won't fail. And the doctor won't always be able to protect the cop, what if the doctor dies?