I would say Leslie Williams (Lee Grant) in "Ransom for
A Dead Man" is right near the top. Her husband marries her, gives her a luxurious lifestyle, sets her up in a successful law practice, quits the state Supreme Court to make her happy, and even seems to treat her civilly after she tells him to get lost, and for all this he gets gunned down.
It's surprising that she didn't try to knock off his daughter as well, considering how much she was taunting her.

My pick would be Dr. Eric Mason in How to Dial a Murder. He had to put in many into planning, and into the training of the dogs. And probably all the while thinking what a massacre it was going to be for poor Charlie. This murder was so senseless. His wife was dead already...maybe at his own hand...and Charlie was no longer a threat to him. It was simply revenge on the part of Mason.
It really was a very gruesome way to kill someone.
And what makes him even more vile is the fact that he was willing to sacrifice his beloved dogs...he must have certainly known that the dogs would have to be destroyed after such a vicious attack.

Let me bring up Dale Kingston. Let's see, kill Uncle Rudy. Drag a naive art student into this with promises of wealth and romance. Trash Uncle Rudy's house. Steal 2 of his paintings. Meet his accessory. Kill her. Fake a car accident. Frame Edna with wrapping paper from Uncle Rudy's house. Frame her with the murder weapon. Finally, plant the stolen paintings in her house to insure this innocent woman's arrest and him becoming the owner of the art collection. All the time sneering at Columbo and manipulating Edna and the family lawyer.

Joe

All of these are strong candidates.

I'll throw in Paul Gerard in "Murder Under Glass".

He manipulated eveybody in sight; blackmailed members of the Restaurant Developers Association; cruelly poisoned one of these members; and even tried to kill off our favourite detective....and of course Columbo hated him!

Let's not forget Paul Galesko (Dick Van Dyke) of "Negative Reaction." It was just not convincing to me that his wife should have been killed, and in addition to that he destroys the life of and frames an ex-convict who was apparently looking to get his life back on the right track.

I think Rip Torn in "Death Hits the Jackpot" was a grade A tossbag. Usually the victims provoke their own murders in some way but this murderer kills his own nephew to steal his lottery winnings.

"grade A tossbag"....I love it!!!! I have no idea what it means...but I love it!

Here in the UK, to toss is to masturbate!!

EEEEK!!!

I'll nominate Nora Chandler. She killed her husband and buried him in the backyard, and did a hit and run on a gossip columnist.

But worst of all - she killed her friend by setting her on fire. THAT is ruthless!

Yeah, Tele, that was pretty horrible. Dogs eating you is one thing, but being burned to death is also just as terrible.......oh yuck!!!