Four former Cuban intelligence agents, interviewed on German television, claimed that Kennedy’s assassin was allegedly a tool of Fidel Castro’s Security Department.

In Washington, meanwhile, a senior attorney who served on the official American investigation — the Warren Commission — reversed his position on the same subject.

William Coleman, a former assistant counsel, had told me before Christmas of a mission that he carried out on the orders of the US Chief Justice, Earl Warren. He had flown to a secret location for a meeting with Señor Castro — a rare event indeed for an American official, even more so given the nature of the discussion. What Mr Coleman learnt, he said, satisfied him — and the Chief Justice when he reported back — that “Castro’s regime had nothing to do with the President’s murder”.

Mr Coleman had spoken clearly, and in the presence of a third party. This week, however, I received a letter from him denying that the meeting with the Cuban leader had ever taken place. This is hard to explain, unless perhaps one notes that Mr Coleman — himself a former Cabinet member — is close to senior officials in the Bush Administration. Perhaps the Bush people, who take a hard line on Cuba, prefer that dark rumours about Señor Castro remain unrefuted.

All the shots that killed Kennedy in Dallas on November 22, 1963, the Warren commission concluded, were fired by Lee Harvey Oswald, a former defector to the Soviet Union and a Castro sympathiser, acting alone.

A second investigation years later, by a congressional committee, reported that there had “probably” been two snipers — one of them Oswald — and thus a conspiracy. As with the Warren commission, the committee said that it found no evidence to implicate Cuba.

The German documentary, aired for the first time last night by Westdeutscher Rundfunk, claims to have found such evidence. Wilfried Huismann, an award-winning film-maker, presented a chilling scenario.

On July 18, 1962, soon after Oswald’s return to America from the Soviet Union, Vladimir Kryuchkov, a future KGB chief, sent a telegram about Oswald to the head of Cuban intelligence, Comandante Ramiro Valdes. Though Oswald was “unstable”, he said, the Cubans should take a look at him.

Señor Valdes’ staff did as their Soviet counterparts suggested, and had their first contact with Oswald in November, a few weeks after the Cuban missile crisis. More contacts followed — directed, according to the documentary, by Rolando Cubela, then a trusted Castro associate. Oswald was supplied with modest sums of money, and acquired a file at Havana headquarters in a section assigned to “Foreign Collaborators”.

The pivotal encounter, the episode most incriminating to the Cubans, took place less than two months before the assassination. Fabián Escalante, a future chief of intelligence, and his nephew Aníbal, the son of a former president of the Cuban Communist Party, are named in the programme as having met Oswald.

The young American said that he wanted to become a “soldier of the Revolution”. To prove it he would kill Kennedy. He was supposedly twice observed in the Cuban Embassy’s garage — a location chosen because the Cubans knew the offices and corridors of their diplomatic mission were riddled with CIA bugs and hopelessly insecure — with another agent of State Security, a tall, thin, black man called César Morales Mesa. He allegedly paid Oswald the less than princely sum of $6,500.

On November 22, 1963, after Kennedy was killed, the Cubans abandoned Oswald to his fate. He had been given certain assurances, presumably of a safe haven, but these were now forgotten. Oswald was arrested by Dallas police, but was shot dead by Jack Ruby, a local nightclub owner while being transferred to the county jail.

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