Season 9, Episode 5 (Spoiler Alert) Uneasy Rest the Crown
The main antagonist and I think his brother-in-law admitted to Columbo that they disposed of the body of his wife's lover in order to cover up her apparent involvement in his murder and the only thing Columbo did was thank them for tightening up a loose end. What? Huh? I'm sure Columbo has been around long enough to know aiding and abetting is kinda illegal - LMAO.