As far as "unsympathetic," I don't know the episode well, but there was Nehemiah Persoff in Now You See Him. You'd think that any detective story where the killer is a former concentration camp officer would have a sympathetic victim, but that's where the story does something original. The victim is a blackmailer, who even has the nerve to very briefly get on the soapbox about that subject, even though HE'S the one keeping Cassidy out of trouble! But my real favorite is Martin Sheen in Lovely But Lethal. Not only does he steal poor Fred Draper's invention, but he toys with Vera Miles, not only by making her think that he can be bought off, but by making her think that she herself is part of his price. Then pulls the rug out, about BOTH things. Regardless of their past together, and who was guilty of what, this showed him in a really nasty light.