Big weakness of this episode. No motive is
ever given and we are not told why Columbo
suspected Hanlon from the beginning. This is
one of the weakest story lines (along with
"Any Old Port in a Storm") but the good acting
makes it a tolerable episode to watch.
Columbo started to suspect Hanlon when he turned the radio off when there was the suggestion that Eric had been murdered. Columbo thought he had "struck a chord." It is a very weak clue and really not a sound basis for Columbo's suspicions.