On Nov. 22, 1963, President John F. Kennedy was assassinated while riding through the streets of Dallas in an open-topped motorcade. With wife Jackie Kennedy by his side, the 46-year-old president was struck by two bullets — one in the head and one in the neck. Former U.S. Marine Lee Harvey Oswald was charged with the murder, and a presidential commission later found that the gunman had acted alone.
But that conclusion has hardly satisfied the public, with JFK’s assassination fueling conspiracy theories for decades to come.
On Thursday, nearly 54 years later, the government is expected to release thousands of long-blocked and classified documents about JFK’s assassination, in a move that could further inflame existing conspiracy theories — or spawn new ones.
Here are three of the top conspiracy theories about JFK’s murder — so far:
1. The grassy knoll
Some say the trajectory of the bullets that struck JFK didn’t align with Oswald’s position on the sixth floor of the Texas School Book Depository, spurring theories that a second gunman — perhaps on the grassy knoll of Dallas’ Dealey Plaza — participated in the shooting.
That theory was given a boost by none other than the U.S. House of Representatives, which voted in 1976 — in the wake of the Watergate scandal — to establish a Select Committee on Assassinations to reinvestigate JFK’s killing.
The House found no evidence of Soviet, Cuban or CIA involvement in Kennedy’s assassination, but did conclude that there was “probably” a conspiracy involving a second gunman on the “grassy knoll,” The Washington Post reported, while pointing out that the theory has since been discredited multiple times.
In 2008, a team of experts used high-tech tools including 3-D computer simulations, artificial human body surrogates and modern blood splatter analysis to determine that Oswald’s perch is the likely origin point of the bullet that killed Kennedy, NBC News reported.
2. LBJ or the CIA
According to other widespread conspiracy theories, JFK’s assassination was plotted by the CIA and/or then-Vice President Lyndon B. Johnson, who was sworn in as president hours after Kennedy was shot.
Some speculate that LBJ plotted Kennedy’s assassination because the vice president feared being dropped from the Democratic ticket in the upcoming 1964 election.
Kennedy’s personal secretary, Evelyn Lincoln, said in her 1968 memoir that Kennedy had in fact planned to replace Johnson as vice president, and that he told Lincoln as much just three days before he was killed.
However, historians and scholars have scoffed at the theory that LBJ orchestrated his boss’s death. Larry Sabato, author of The Kennedy Half-Century, told the Daily Beast the theory has no “hard evidence” and is “ridiculous.”
Others believe the CIA had Kennedy killed because the agency opposed some of the president’s positions on Cuba and Communism, particularly his refusal to offer air support for the failed Bay of Pigs invasion, a CIA mission to overthrow Cuban Prime Minister Fidel Castro, Business Insider reported.
The new documents are expected to shed light on the CIA’s response to the assassination — and could finally put this conspiracy to rest.
Although this theory has been the hardest to disprove, Mark Fenster, author of Conspiracy Theories: Secrecy and Power in American Culture, told the Daily Beast he’s deeply skeptical of it because “I’m not convinced that the CIA of that era has shown itself as an organization to be exceptionally competent at doing anything but ruining other countries and people’s lives in openly secretive ways. Pulling off a JFK hit and keeping it secret this long would be the mark of an incredibly competent plot.”
3. Ted Cruz’s dad
A theory resurfaced by President Donald Trump on the campaign trail claims that Sen. Ted Cruz’s father, Rafael Cruz, was somehow involved in JFK’s killing and had been spotted with Oswald before the shooting.
Taking aim at his 2016 rival’s father, Trump told Fox News in a telephone interview last year, “His father was with Lee Harvey Oswald prior to Oswald being, you know, shot. I mean the whole thing is ridiculous. What is this? Right? Prior to his being shot. And nobody even brings it up. I mean, they don’t even talk about that — that was reported. And nobody talks about it.”
This theory has also been widely discredited, with FactCheck.org pointing out that Trump was citing a National Enquirer article. The piece quotes a photo expert who said an unidentified man spotted handing out Fidel Castro leaflets with Oswald has “more similarity than dissimilarity” to the elder Cruz.
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Speculation over JFK’s assassination is so popular that the majority of Americans have actually bought into the theories. A 2013 Washington Post-ABC News poll found that 62 percent of Americans believe Kennedy’s murder was part of a broader plot.
Meanwhile, Jackie Kennedy’s former Secret Service agent, Clint Hill, told PEOPLE this week that he believes the former first lady would support the release of the long-secret documents in the name of transparency.
“It was my understanding that she wanted all the information released,” he said. “She wanted people to have as much information about what actually happened as possible.”