What is odd about "Friend in Deed" is
that we are never shown any real hostility between them. He mildly complains that she gives away money as a do-gooder, but, unlike "Negative Reaction", we are not told that he really wants to get away from her or that he needs her money.

That final taunt, that "[her] judgment is not so good" as he pushes her head under the water is particularly cold. It's pretty clear he was referring less to her generosity with money than to her decision to marry him.

Barry Mayfield of "A Stitch in Crime" and Jarvis Goodland of "The Greenhouse Jungle" come to mind.

Miles Jannus. Very cold. Also, he used his bare hands.

Some motives are real clear and understandable. Some start out as accidents, such as Death lends a Hand. Some, such as Columbo likes the Nightlife, graduate to a second real murder.

I don't think Adrian Carsini, in a fit of rage really meant to kill his half brother.

But Max Barsini, despite the comfortable life style with a new wife and a nymph when he wanted it, was really cold blooded when his ex-wife said she was going off.

Yes, there were the old dreams. But they were divorced. She was not depicted as holding them over him. I didn't get the direct impression that he had a hold over her to continue living next door up to that point.

As far as I've thought about it, I've always thought of Mark Halperin too. He's one of the few I can think of who actually makes witticisms (about both killings). When his friend Hugh is worried about what he'll do to the blackmailer, Mark says very innocently, "Why, Hugh - I'm no more violent that you are." And of course when Hugh, referring to his (partly accidental) killing, says, "I knew I should have called the police," Mark says, "You DID call the police." Two pretty great lines.