I was wondering, is there an episode where the killer is nice to Columbo all the way untill the end? Like being patient with him, and not being on such "high horses" all the time?
He isn't consistently nice to Columbo, but there's a "friendly" final scene with Marshall Cahill. Of course, it has Columbo feeling bad about the imitation frame-up of Marshall's son Neil, but maybe it would have been like that either way.
Kay Freestone is nice to him right until that final scene when he annoys her through the tv screens and thats the only point where she really loses it with him.