I recall that the show always played fair, that the mistake the killer makes is always visible to the viewer paying attention. That was always one of the fun parts about it, watching the murder, and trying to figure out what little detail will be the essential clue.
Two more favorites that haven’t been mentioned so far:
“Any old Port in a Storm” probably had the most sympathetic murderer, but “Murder, Smoke, and Shadows” completely dazzled me.
Oh, and the episode with Patrick McGoohan as a spy gave some nods to “The Prisoner”, which had been a favorite show, too.