In November 1963, Cuban intelligence officer Florentino Aspillaga was posted in a little hut near a Cuban beach where he operated listening equipment trained on Miami and CIA headquarters in Virginia. On the morning of Nov. 22, Mr. Aspillaga—who would defect to the U.S. in 1987—said that he was ordered "to stop all your CIA work, all your CIA work." He was instructed to "put all of my equipment to listen to any small detail from Texas. They told me Texas."
Did Castro know that Lee Harvey Oswald was about to assassinate President Kennedy? Brian Latell, a veteran CIA Cuba analyst who spent 15 hours interviewing Mr. Aspillaga for his newly revised "Castro's Secrets," (Palgrave MacMillan), makes a strong case that he did.     
Mr. Latell takes readers through a half-century of Cuban espionage by interviewing a dozen high-ranking Cuban defectors and numerous former CIA officers. He calls Mr. Aspillaga "the most knowledgeable Cuban defector ever to change sides." He also pored over thousands of pages of declassified CIA documents and gained access to the unpublished memoir of Thomas Mann, the U.S. ambassador to Mexico in 1963, who had reason to suspect an Oswald-Cuba connection.
Mr. Latell set out to tell the story of Cuba's "intelligence machine," which outmaneuvered the U.S. for many years. In the process he uncovers startling details that suggest that Cuba fueled Oswald's maniacal desire to prove himself worthy of Castro's revolution during the American's visit to Mexico City in the fall of 1963. Mr. Latell also presents strong evidence that the Johnson administration and higher-ups in the FBI and the CIA ensured those details were kept from the Warren Commission.
WSJ's Mary Anastasia O'Grady explains the relationship that JFK assassin Lee Harvey Oswald had with the Cubans along with a trip he took to Mexico City in late September 1963 to try to secure a visa to Cuba. Photo: AP

The Kennedy administration was desperate to eliminate Castro. The 1961 Bay of Pigs invasion had failed and by August 1963, according to Edward Jay Epstein —a renowned expert on the killing of the president and author of the recently released book "The JFK Assassination Diary"— Richard Helms, though not yet CIA director, was "receiving almost daily phone calls from [Attorney General Robert Kennedy ] demanding to know what actions he was [taking] to remove Castro from power." The agency recruited Rolando Cubela, a revolutionary insider, to do the job.
But Cubela was a double agent. And on Sept. 7, just after Cubela agreed to help the Americans, Castro gave an interview to an AP reporter in which he put the U.S. on notice that "aiding terrorist plans to eliminate Cuban leaders" would mean that "they themselves will not be safe."
Castro didn't need to look far for a willing partner to back up those words. It is "known with near certainty," writes Mr. Latell, that Cuba had "opened a dossier" on Oswald in 1959, while he was stationed at the Marine Corps Air Station El Toro, in Southern California. Oswald was enamored of the Cuban Revolution, and he had made contact with the Cuban consulate in Los Angeles.
On Sept. 27, 1963, Oswald checked into the Hotel Comercio in Mexico City for a five-night stay. He tried to get a visa from the Cuban embassy to travel to Havana. He had a fling with an embassy employee and probably spent time with others who were intelligence agents. When his visa was not forthcoming, witnesses said he went on a rant at the embassy, slammed the door and stormed off.
According to Mr. Latell, during his Mexico City stay Oswald twice visited the Soviet consulate where he met with "an officer of the notorious Department 13, responsible for assassination and sabotage operations." The KGB was training Cuban intelligence at the time, and "it seems certain that [Oswald's] intelligence file in Havana was thickening."
Castro's claim about Oswald—in a speech 30 hours after Kennedy was shot—that "we never in our life heard of him" was a lie. Indeed, in a 1964 conversation with Jack Childs —an American communist who had secretly been working for the FBI—Castro let it slip that he knew of Oswald's outburst while at the embassy in Mexico City and said that the ex-Marine had threatened to kill the U.S. president.
When Warren Commission staff asked Ambassador Mann about the Hotel Comercio's reputation as "a headquarters for pro-Castro activities," Mann answered: "it was not known generally at all . . . [but] only in intelligence circles."
For Mann, it was too convenient that Oswald landed at that hotel. He pushed for more information about Oswald's Mexico City sojourn. In his memoir, however, he wrote: "The Embassy received instructions to cease our investigation of Oswald's visit to Mexico and to request that the Mexican government do the same." Mann asked for reconsideration and was denied. The Warren Commission was never told of the CIA plan to take out Castro.
All of this leaves a giant hole in the official narrative about the assassination. Mr. Latell concludes that "Castro and a small number of Cuban intelligence officers were complicit in Kennedy's death but that their involvement fell short of an organized assassination plot." Instead they "exhorted Oswald," and "encouraged his feral militance."