Can anyone tell me the name of the episode where an actor assumes a female character and when in character becomes a murderer?
Thanks in advance!

Are you sure this is a Columbo episode? It don't sound familiar. The only episodes that I can think of that deals with actors is Nora Chandler in Requiem for a Falling Star, Grace Wheeler in Forgotten Lady and Ward Fowler in Fade In To Murder.

Sex and the Married Detective? The murderer disguises herself as the “Lady in Black”.

You could be right on this one, BR. I heard "actor" and incorrectly assumed that Kyra meant "male"....but yeah, I think when Dr. Allenby becomes call girl "Lisa" and kills her boyfriend, is the only time I recall even something close to this question happening.

hmmmm...if this is a serious question, then I want to say you have it mixed up with a Brian De Palma movie called "Dressed to Kill"...Michael Caine cross-dressed and became quite a lethal killer when doing so...