[Lonesome in Massachussets]

Columbo knows who did it within thirty seconds of arriving at the scene of the crime. The next one hour and fifty eight minutes are watching him hoist the perpetrator on his own petard and final ninety seconds are Columbo gloatingly skewering his prey.

[period end of story]

I don't think he knows who really did it until near the end of the show.

We know who did it right from the start. But he must attract the killer into the wonderful web that he creates.

[laotzu]

Columbo knows who did it within thirty seconds..

Thanks. I was waiting for a place to tee-off.

My favorite episode ends with the perp asking when Columbo first suspected him, and is told "about five seconds after I met you".

"Ridiculous!" the perp says, "how can this be true?"

Columbo tells him "when I called you from the scene, and told you the man you had supper with had died of food-poisoning, and asked you to come right over.....you know what you did? You came right over. You didn't ask what kind of poison, you didn't go to a doctor or hospital, you didn't ask any questions at all. You came right over. That's the damndest act of civic responsibility I ever saw!"

I loved that show.