The film, shown to journalists in Berlin on Wednesday, says Oswald traveled to Mexico City by bus in September 1963, seven weeks before the Kennedy shooting, and met agents at the Cuban embassy there who paid him $6,500.
Oscar Marino, a former Cuban agent and a key source for the documentary, told Huismann that Oswald himself had volunteered for the assassination mission and Havana had exploited him.
"Oswald was a dissident. He hated his country...Oswald offered to kill Kennedy," Marino said in the film.
"He was so full of hate, he had the idea. We used him...He was a tool."
He said he knew with certainty that the assassination was an operation of the Cuban secret service G-2, but would not say if it was ordered by President Fidel Castro.
Laurence Keenan, an officer of the Federal Bureau of Investigation (FBI) who was sent to Mexico City immediately after Kennedy's death to investigate a possible Cuban connection, said he was recalled after just three days and the probe was aborted.
"This was perhaps the worst investigation the FBI was ever involved in," Keenan said. "I realized that I was used. I felt ashamed. We missed a moment in history."
Keenan, 81, said he was convinced Kennedy's successor, Lyndon Johnson, blocked further investigation because proof of a Cuban link would put him under irresistible pressure to invade the island, a year after the Cuban missile crisis had brought the United States and Soviet Union to the brink of nuclear war.
"Most likely there would have been an invasion of Cuba which could have had unknown consequences for the whole world," he told journalists at the screening, saying that was why Johnson preferred to accept Oswald was "a crazed lone Marxist assassin."
Interviewed for the film, Alexander Haig, then a U.S. military adviser and later secretary of state, quoted Johnson as saying "we simply must not allow the American people to believe that Fidel Castro could have killed our president."
"And the reason was that there would be a right-wing uprising in America, which would keep the Democratic party out of power for two generations," Haig said.
He added that Robert F. Kennedy, brother of the assassinated president and attorney general in his administration, had personally ordered eight attempts on the life of Castro, who is still in power to this day.
Cuban and Russian sources interviewed in the film say the KGB alerted the Cubans to Oswald in mid-1962 after he left the Soviet Union, where he had lived for three years, and returned to the United States with his Soviet wife and their daughter.
Cuban intelligence first made contact with Oswald in November 1962, according to the film.
Huismann also unearthed a U.S. intelligence report shown to Johnson which said Cuban secret service chief Fabian Escalante flew via Mexico City to Dallas on the day of Kennedy's assassination, and back again the same day.
Tracked down by the film maker, Escalante denied he had been in Dallas and evaded questions about Cuba's alleged role. "What is truth, what are lies?" he said, smiling.
This film will certainly add to the lore of the Kennedy assassination. Here's hoping that its a smoking gun that will finger Fidel...
One thing for sure though is it won't stop the Castro fetishization by the American Left.