On November 24, 1971, a man using the alias Dan Cooper hijacked a Northwest Orient flight, extorted $200,000 in ransom, and then parachuted from the plane. He was never found. The only unsolved air piracy in US aviation history.
Teamsters union leader Jimmy Hoffa disappeared on July 30, 1975, from a parking lot in Bloomfield Township, Michigan. He was presumed murdered, likely by the mob, but his body has never been found.
On March 18, 1990, two men posing as police officers entered the Isabella Stewart Gardner Museum in Boston and stole 13 works of art worth an estimated $500 million, including pieces by Vermeer, Rembrandt, and Degas. The theft remains unsolved.