Think the CIA played a role in covering up the John F. Kennedy assassination? Now an important source agrees with you: the CIA. According to an article written by the agency's senior in-house historian, the CIA purposely held back information from the Warren Commission, Politico reports. John McCone, then the agency's director, apparently failed to tell the commission about agency plots to murder Fidel Castro (including ones involving the Mafia). So the commission never knew to ask whether Lee Harvey Oswald had Cuban comrades dead-set on retaliating against the US president. The commission famously concluded that Oswald acted alone, spawning decades of conspiracy theories involving Castro, the Mafia, the CIA, the Soviets, and even President Lyndon B. Johnson.
Seems the White House nudged McCone along: He "shared the administration’s interest in avoiding disclosures about covert actions that would circumstantially implicate [the] CIA in conspiracy theories and possibly lead to calls for a tough US response against the perpetrators of the assassination," reads the article, which was published in a CIA internal magazine in 2013 and declassified (with 15 redactions) last fall. McCone also apparently didn't reveal that the CIA may have been communicating with Oswald before the killing, and was illegally reading his mail after he tried defecting to the Soviets in 1959. The article, by CIA historian David Robarge, calls McCone's actions "benign" but says the cover-up played a big role in "undermin[ing] the credibility of the commission." (Click for a list of the most pervasive JFK conspiracy theories.)