I love in Death Lends a Hand:

"I have a feeling when we find our friend...we'll see he has a bad temper" (words to that effect)

the scene where Falk and Culp are at Culps desk....where Columbo brings him the "files" personally...is one of my fave acted scenes....where Brimmer feigns appreciation for the files, claiming they will help a great deal

I have so many and I agree the main heart of the entertainment is when the interplay between the murderer and Columbo develops into the veiled accusations. The more powerful the murderer, the more aloof and self important the better. One of my favourites is when (death lends a hand) Columbo says "What a coincidence! There we were talking about left handed people and there you are left handed". I think that is a fantastic moment particularly the way he does it, with such feigned surprise! Exquisite!

The climax of "The Bye Bye Sky High I.Q. Murder Case" is a great example, where Columbo goes through just about the whole way in which the murderer covers up the crime, and then Oliver Brandt fittingly finishes it for him.

Once in a while he's talking that way to someone other than the killer. There's the LOVELY BUT LETHAL scene between him and Bruce Kirby when he says so casually "What do they call that - octagonal?"

There's one in By The Book when Columbo is at Ken's house and he notices Ken opened his mail....some where in the dialog columbo slips in the line " I know you did it" but "Could you go over where you were again".