In a way, one of them goes to both extremes, and that's Beth Chadwick.
She's about the only one to confess to the killing (though not as a murder) at the very beginning, but she's about the only one you see being cleared in a courtroom!
So I can't help liking it when she tells Columbo to stop coming to see her. She says it very "firmly," and you can hardly blame her.
Even though I'm one of its defenders, there's MIND OVER MAYHEM.
In spite of all the blunders Marshall Cahill makes, what makes him confess is Columbo arresting his son on a trumped-up charge (which he later ADMITS is a trumped-up charge), so why WOULD'T Marshall confess? (A little like Ned Diamond confessing to cover for Grace Wheeler, except that it's covering for someone who's actually innocent.) And according to Columbo, he probably couldn't get Marshall any other way, as in evidence.