What is Columbo's catchphrase?

Answer 1

"Just one more thing..."

Columbo's catchphrase marked the point at which he'd found his prime suspect; all that follows is finding the proof.

Columbo would put his quarry at ease by coming across as harmlessly bumbling, only to baffle them with his wit and wiles. Getting ready to leave, having given them little to worry about with a few easy questions at the launch of a new investigation, he would let them initially shrug him off to enjoy a moment of relief that their dastardly crime had avoided detection, underestimating the dull and sloppy-looking detective, he would turn and say "just one more thing" with a raised finger and an expression of profound confusion.

At this point, the viewer knew that Columbo was on to the suspect. From here the killer would be forced to perform all sorts of contortions with their version of the truth, compelled to provide explanations for holes in the case, or embellish their increasingly weakened version of events until they were finally completely out-witted and hung by their own convolutions.

The Columbo series approached the murder-mystery detective serial in a different way to most, eschewing the traditional 'whodunnit' format in favour of showing everything to the viewer from the start of the episode.

Despite knowing who the killer is, the viewer is only truly informed of the relevance of the killer's actions through Columbo's insight and his ability to sleuth his way competently to the truth. Adept at misdirecting his suspects, he sometimes even performs a little (or large) sleight-of-hand to truly confound them.