I interpreted it to be the sane person will have the role the pm assigned them. The insane ones may or may not have the role that the pm assigned them.
Say I was assigned cop but am insane. I go to check someone and end up killing them. This means I am actually the killer and not a cop.
Say I was assigned cop but am insane. I go to check someone and end up killing them. This means I am actually the killer and not a cop.