Factual error: In common with a number of characters in numerous episodes, Columbo hopelessly contaminates crucial evidence - at the end of the episode he handles the surgical gloves used by the killer with bare hands.
Other mistake: In the cabin, Mrs. Danziger says he can pick up a pair of golf gloves in Acapulco. Golf gloves are normally sold as singles, not pairs. Very few people wear two golf gloves except in quite cold weather.
Character mistake: The crew of the ship is British. Most of them refer to Columbo as "Leftenant," but the doctor switches between "Leftenant" and "Lootenant."
Other mistake: The captain and the doctor play very fast and loose with medical records privacy, letting Columbo see them and discussing them.
Factual error: The nurse is smoking a cigarette in the sick bay. By 1975, when the show was recorded, that would not happen.
Factual error: The nurse brings Danziger a sedative and takes his blood pressure. She has her stethoscope in her ears backwards. A qualified nurse would not make that mistake. When she comes in after the murder to do it again, she has the stethoscope in correctly.
Factual error: Several times, the revolver used to murder the singer is referred to as a "Weatherby" or "British Weatherby." Weatherby is an American manufacturer of rifles and shotguns; they do not make handguns. The revolver used is a Webley, which is of British manufacture.
Other mistake: When Rosanna's body is brought to the ship's medical room, the doctor confirms that there are no bruises on the body, but she had been forcibly slapped in the face earlier that day by Mr Danzinger (Robert Vaughn). The slap was hard enough to knock her over therefore a bruise should be visible, even through make-up.
Answer: "Apparent" drowning answers your question - things are not always as they seem. Drowning could be accidental, but it could also be a murder in disguise. Moreover, the actual cause of death has not yet been determined - accident, suicide, murder, or natural cause (e.g, heart attack while swimming). Columbo would be there to investigate if anything looks unusual for it to be a mere drowning or if there is evidence or suspicion of something else.
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This was just on TMZ.com's "Aaron Carter Dead at 34" (11/05/2022): "Law enforcement sources tell TMZ... homicide detectives have been dispatched to the scene but we have no information or evidence of foul play. It's standard operating procedure for homicide detectives to investigate such [drowning] death scenes."
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