In Etude In Black Alex tries to unconvince Columbo that he saw him pick up the flower at Jenifer Welles' place. He saw him do it!
Probably the whole script between Columbo and Ward Fowler..in Fade In To Murder. Especially towards the end..where Fowler is admitting to stuff...I know he knows that Columbo knows...but at least don't confess to stuff that you may not have to.
And not to be picky...but think of the scene from Candidate For Crime....the one where Columbo is visiting Hayward at his headquaters, and Columbo does that lame demonstration of the cars on the back of the "Vote For Hayward" poster..........well..there were many other possibilities of how the car could have been parked....I think Columbo was grasping at straws here. ..............this would be a reversal on your stupid murderer thingys.