I was thinking "Not only is it very tenuous, impossible to prove" from "Death Lends a Hand" although of course the exact initials did not work out.

good try. not right . The episode is where partick mcgoohan is a secret agent.
Best wishes and thanks for trying so hard.

"No one is ever who they say they are"

(I couldn't have done it without the hints.)

Let's have another one, Bernie!

fantastic - very well done!!! new one to follow shortly. bernie

Hey Bernie, you really need to find yourself some kind of a life.

hey ike - lots of people have offered me very creative and interesting answers (not just on the forum but many people I know who share our admiration of columbo) so please don't give up. Have another go. Answer released next week. Clue Murderer Patrick mcgoohan.
Best of luck and please don't give up too soon.