Just under 54 years ago, two years into his presidency, President John F. Kennedy was assassinated on a visit to Dallas, Texas.
An investigation by the Warren Commission determined a former US Marine named Lee Harvey Oswald shot Kennedy from a nearby book depository, but the murky facts of the case have led to a number of alternate theories.
They include a CIA conspiracy, a mafia hit job, a covert operation by Lyndon B. Johnson, and more.
In anticipation of the National Archives releasing 3,100 documents related to the assassination on Oct. 26, here are the top theories that have swirled ever since.
The CIA theory
People who believe the CIA was behind Kennedy's assassination speculate the agency strongly opposed a number of the president's stances on Cuba and Communism.
The theory posits that Kennedy's refusal to offer air support for the failed Bay of Pigs invasion, a CIA-sponsored mission to overthrow Fidel Castro, triggered the CIA to eliminate Kennedy from the picture altogether.
Theorists tend to believe the CIA set Oswald up as its scapegoat.
The Mafia theory
A related theory suggests the CIA worked with the Mafia to have Kennedy killed. At the time, the two organizations had a shared interest in overthrowing Castro, as the Mafia held a number of investments in Cuban casinos at-risk of being shut down.
Government documents show the CIA did work with the Mafia to take down Castro; some conspiracy theorists claim the two also worked together, along with anti-Castro Cubans, to assassinate Kennedy.
The Cuban exile theory
Members of the Cuban invasion force meet President and Mrs. Kennedy in 1962. Photo: John F. Kennedy Presidential Library
Some believe the effort was far less sophisticated than a federal conspiracy, but carried out by a group of rogue Cuban exiles who saw the failed Bay of Pigs invasion as sufficient evidence that Kennedy was unfit as president.
Between 1959, when the Cuban Revolution brought Castro to power, and Kennedy's assassination in 1963, his popularity among exiles had eroded considerably. In October of 1963, anti-Castro Cubans met with right-wing Americans to discuss frustrations with Kennedy.
Theorists speculate the meeting may have been a tipping point for the assassination a month later.
The Lyndon B. Johnson theory
One theory speculates that LBJ feared getting dropped from the Democratic ticket in the 1964 election so intensely that he plotted to have Kennedy assassinated.
According to a 1968 memoir written by Kennedy's personal secretary, Evelyn Lincoln, it is true that Kennedy planned to replace Johnson as vice president. Kennedy told Lincoln as much on Nov. 19, 1963 — three days before he was killed.
Conspiracy theorists point to the timeline as partial evidence that Johnson might have had a hand in orchestrating the murder.
The KGB theory
President Kennedy meets with Chairman Khrushchev at the U. S. Embassy residence, Vienna. U. S. Dept. of State photograph in the John Fitzgerald Kennedy Library, Boston. 03 June 1961
Some theorists believe a band of Soviet officers carried out Kennedy's assassination, directed by Premier Nikita Krushchev.
Toward the end of the 1962 Cuban Missile Crisis, Krushchev was ultimately forced to remove the intercontinental ballistic missiles he'd deployed in Cuba due to US militaristic threats against the Soviet Union.
Conspiracy theorists claim the move motivated Krushchev to have Kennedy killed.