A new documentary exploring the death of John F Kennedy claims his assassin was directed and paid by Cuba.
Kennedy's assassination was a defining moment in US history
Rendezvous with Death, based on new evidence from Cuban, Russian and US sources, took three years to research.
One source, ex-Cuban agent Oscar Marino, said Havana had exploited Lee Harvey Oswald, who was arrested but shot dead before he could be tried.
Conspiracy theories on the killing have variously accused Cuba, Russia and the US of acting alone or jointly.
According to Oscar Marino, the Cubans wanted Kennedy dead because he opposed the revolution and allegedly sought to have its leader Fidel Castro killed.
Mr Marino told film director Wilfried Huismann that he knew for certain the assassination was an operation run by the Cuban secret service G2, but he declined to say whether it had been ordered by Mr Castro.
Cuban intelligence made contact with Oswald after being alerted by the Russian KGB in 1962 when he returned to the US after living in the Soviet Union for three years, Cuban and Russian sources say.
"He [Oswald] was so full of hate, he had the idea. We used him," Mr Marino said.
A possible Cuban connection was investigated by the US immediately after Kennedy's death.
But an FBI officer sent to follow the Oswald's trail during a visit to Mexico was recalled after only three days and the investigation called off.
Laurence Keenan, now 81, said it was "perhaps the worst investigation the FBI was ever involved in".
"I realised that I was used. I felt ashamed. We missed a moment in history," Mr Keenan said.
Oswald, an ex-marine, was a Communist sympathiser
Veteran US official Alexander Haig told the filmmaker that Kennedy's successor, Lyndon B Johnson, believed Cuba was to blame and feared a pronounced swing to the right if the truth were known that would keep the Democrats out of power for a long time.
Mr Haig - a US military adviser at the time and later a secretary of state - told the filmmakers Johnson said: "We must simply not allow the American people to believe Fidel Castro could have killed our president."
"He [Johnson] was convinced Castro killed Kennedy and he took it to his grave."
John F Kennedy, the 35th US president, was assassinated as his motorcade drove through Dallas in November 1963.
Lee Harvey Oswald, an ex-marine sharpshooter who worked in a book warehouse overlooking the assassination, was arrested but killed shortly afterwards.
He had a Russian wife, called himself a Communist and agitated on behalf of Castro's Cuba.