Many criminals made the mistake of underestimating Lieutenant Columbo, a homicide investigator with a crumpled trench-coat and a beat-up car, who certainly acted as an incompetent bumbler.
But he was so polite to every suspect, and he talked so much about his wife (who we never got to see on any episode, but who many believe later had her own show, starring Kate Mulgrew, later of Star Trek: Voyager fame) that he lulled even the shrewdest murderer into a false sense of security.
And although the audience had witnessed the murder in the beginning of each episode, it was still a surprise to see what mistakes the killers had made during the seemingly perfect murder.
Viveca Scott, the founder of Beauty Mark Cosmetics, is being threatened by her rival David Lang. When he finds out that her revolutionary cream formula actually removes wrinkles, he has the formula pirated.
Wine producer Adrian Carsini discovers that his younger brother Enrico plans to sell the family vineyards to pay his playboy-life debts, and sets out to murder him. He locks him in a wine vault and turns off the air and conditioning, then drags the body out to the ocean and makes it look like Enrico died during a scuba-diving accident. Columbo is suspicious of the contradictions that show up in the autopsy, and soon realizes that Adrian is the murderer. The final clue is the wine that was spoiled when the vault's air conditioning was turned off. Only Adrian could tell the difference, so Columbo secretly gets him to sample the wine and declare it unfit. Once Adrian realizes his wines were ruined, he is forced to throw them over a cliff, as Columbo looks on. In the end, Columbo takes in a relieved Adrian, confessing that Carsini is one of the few killers he was reluctant to bring in.
A Senate Candidate running for office kills his campaign manager by making it look like he was the target for the killer's bullet.
A film maker kills one of his clients. in a break, during the screening of a new ad campaign
A publisher hires a Vietnam vet to kill his star author and thus give himself an alibi before the writer can defect to another publisher.
Dr. Marshal Cahill, head of a think tank, is forced to protect his plagarizing son by killing the professor, Nichols, who discovered the plagarized information. Cahill programs a robot to take his place during a war game exercise that he runs from an isolated room, then fakes a hit-and-run accident on Nichols and plants evidence to make it look like a drug theft gone awry.
The first thing Columbo notices upon arrival is a match burned down to the base - something Columbo knows well because it's how you light a cigar. And Dr. Cahill is the only other cigar smoker around. There are a lot of other little things that Columbo notices as well, and with the help of a child prodigy he discovers how Cahill used the robot to provide himself with an alibi. But without one major clue, Columbo arrests the son to force Cahill, who was willing to kill for his son, to confess his crime to protect the boy.
A Country and Western singer kills his overpowering wife in a plane crash while he parachutes to safety.