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Chabal2
Since: Jan, 2010
2022-09-13 21:36:14
It happens in Sherlock Holmes, but for legitimate questions about a single point (such as "David" in The Crooked Man or the murderer's plan in Hound of the Baskervilles).
Might be worth troping.
Scorpion451
(Edited uphill both ways)

Usually part of golden age detective fiction. The murder has been solved, and almost everything is wrapped up. Except, one of the characters suddenly realizes, one last thing. They ask the inspector who explains this final detail.
In the worst case this results from the writer realizing a plot hole at the last minute. In other cases, it's a red herring, that can be cleared up now that the murder has been revealed.
I can't think of any straight examples, although I think it pops up often in Agatha Christie novels. I do remember it was parodied in an episode of Hamish and Dougal.