It means that something happened and no one can figure out how or why it happened. Sometimes police cases become unsolved mysteries because there is not enough evidence to prove something happened.

....LET'S GO THROUGH WITH ONE TOPIC....

THE BERMUDA TRIANGLE

The Bermuda Triangle is a mythical section of the Atlantic Ocean roughly bounded by Miami, Bermuda and Puerto Rico where dozens of ships and airplanes have disappeared. Unexplained circumstances surround some of these accidents, including one in which the pilots of a squadron of U.S. Navy bombers became disoriented while flying over the area; the planes were never found. Other boats and planes have seemingly vanished from the area in good weather without even radioing distress messages. But although myriad fanciful theories have been proposed regarding the Bermuda Triangle, none of them prove that mysterious disappearances occur more frequently there than in other well-traveled sections of the ocean. In fact, people navigate the area every day without incident.

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