If I am not mistaken, within the original 45 episodes there are four murderers who go for a ride in Columbo's car. Can you name them without making the mistake of including Robert Vaughn's Charles Clay from "Last Salute to the Commodore?" (Remember, he did not kill anyone.)
That's too easy, but you might recall Columbo rode with Bart Keppel in his black Continental to the 2nd crime scene in "Double Exposure", so that doesn't count.
And Tommy Brown (from "Swan Song"). Although we only see them just sitting in Columbo's car, we have to infer that they eventually did drive away together!
do we have to actually see them in the car?
if not i would say ruth lytton from old fashioned murder, because there were no uniformed police around, and columbo escorts her out the door...assumedly to drive her himself to the police station.