Doctor Bart Kepple seems to have something of a break down at the end. He starts of with the confident "without my help you would have never solved it" before breaking into a chuckle and then a laugh but by the freeze frame his expresion is rather manic. I could well imagine he jumped up and tried to attack Columbo.
"Junior" is very unpredictable when they're on the tram going up to pinewild. He thought there was a bomb in the cigar box, he was capable of anything. At one point he even opens the tram door.
Note: last month during the holiday season I heard an old, classic Christmas episode on the radio starring Roddy McDowall. Who was very very young at the time. I believe the date was sometime in the 1950s.