"Columbo" has had its share of fantastic guest actors as murderers: Robert Culp, Patrick McGoohan, Robert Conrad, Lawrence Harvey, Janet Leigh, Martin Landau, and many more. But for my money, Jack Cassidy and his three turns as a "Columbo" killer make for the best episodes in the series.
He has saved the best for last, in his final "Columbo" appearance. He plays Santini, the great magician (and a former Nazi concentration camp guard). Threatened with exposure, he kills the club manager who is blackmailing him...all while he appears to be in the middle of performing on-stage. Cassidy's interplay with Falk is as good as always, with Santini wishing he could make Columbo disappear. Watch Falk's reaction after Santini escapes from the handcuffs on-stage. "I knew you could do it," has never been so loaded a phrase. The final reveal, where Columbo exposes Santini using his own trick is priceless. You had to love Cassidy's face, as he realized he was bested by this little rumpled man in a raincoat.
Speaking of the raincoat...this is the episode where Mrs. Columbo tries to replace the beloved brown coat, only to have Columbo go to great lengths to leave it behind wherever he goes. "The coat - I can't, I can't think in the coat!"