The assassination of civil rights leader Martin Luther King Jr. in 1968, which has also been the subject of numerous conspiracy theories.
The identity of the "D.B. Cooper" hijacker, who extorted $200,000 in ransom money and then parachuted from a plane in 1971, never to be seen again.
The fate of the "Lost Colony" of Roanoke Island, where a group of English settlers disappeared without a trace in the late 16th century.
The Zodiac Killer, a serial killer who operated in California in the late 1960s and early 1970s and who taunted police with cryptic letters and ciphers.
The Roswell UFO incident of 1947, in which a mysterious object crashed in New Mexico and has been the subject of numerous theories about extraterrestrial life.
The identity of "Jack the Ripper," a serial killer who terrorized the streets of London in 1888 and whose true identity has never been definitively proven.
The assassination of President John F. Kennedy in 1963, which has been the subject of numerous conspiracy theories.
The disappearance of Amelia Earhart, a pioneering aviator who vanished during a flight over the Pacific in 1937.
9 Unsolved Mysteries Of USA | 9 Unsolved Mysteries Of USA