We've noted before that Lt. Columbo is better at breaking the killer's alibi than at finding solid proof of a killer's guilt. Even watching this episode, when Columbo asked Franklin why he drove back to the city instead of flying back to console Mrs. Ferris, I thought of an obvious answer: Because he didn't want to leave his car behind!
But asking the question rattled our oh-so-smooth killer, and got inside his head. Over the course of the episode, his demeanor changed from being condescending toward Columbo to being irritated that he wouldn't go away, having to come up with an explanation for every query Columbo came up with.
I often thought the killers in Columbo stories try too hard to answer every one of his questions. Sometimes, they should have said, "I don't know" instead of showing off how smart (they think) they are.
I've also noticed that the killers in the Columbo stories try too hard to help him, which makes Columbo suspicious of them if he isn't already.
If they don't sign confessions, some of the solutions are so convoluted that there would be a lot of hung juries.