What about the Murder gamemode from Garry's Mod?
How they do it in Gmod (correct me if I'm wrong):
Make it so everyone is a bystander except one person (that one person is the murderer). Each person is able to talk until they get murdered. The murderer is able to sprint by holding shift or some other key and the bystanders would know it's the murderer by that trait. One bystander is given a gun to shoot the murderer. Other bystanders could find a gun themselves by collecting 5 hidden props or by picking up a gun dropped by a murdered bystander. The gun should take a few seconds or so to reload after each shot.