Documents never seen by the Warren Commission have revealed that some Mafiosi worked with the CIA on assassination attempts against Cuban leader Fidel Castro. CIA documents released in 2007 confirmed that in the summer of 1960, the CIA recruited ex-FBI agent Robert Maheu to approach the West Coast representative of the Chicago mob, Johnny Roselli. When Maheu contacted Roselli, Maheu hid the fact that he was sent by the CIA, instead portraying himself an advocate for international corporations. He offered to pay $150,000 to have Castro killed, but Roselli declined any pay. Roselli introduced Maheu to two men he referred to as "Sam Gold" and "Joe." "Sam Gold" was Sam Giancana; "Joe" was Santo Trafficante, Jr., the Tampa, Florida boss and one of the most powerful mobsters in pre-revolution Cuba. Glenn Kessler of The Washington Post explained: "After Fidel Castro led a revolution that toppled a friendly government in 1959, the CIA was desperate to eliminate him. So the agency sought out a partner equally worried about Castro—the Mafia, which had lucrative investments in Cuban casinos."
Some conspiracy theorists have alleged a plot involving elements of the Mafia, the CIA and the anti-Castro Cubans, including author Anthony Summers and journalist Ruben Castaneda. Castaneda wrote: "Based on the evidence, it is likely that JFK was killed by a coalition of anti-Castro Cubans, the Mob, and elements of the CIA." In his book, They Killed Our President, former Minnesota governor Jessie Ventura also concluded: "John F. Kennedy was murdered by a conspiracy involving disgruntled CIA agents, anti-Castro Cubans, and members of the Mafia, all of whom were extremely angry at what they viewed as Kennedy's appeasement policies toward Communist Cuba and the Soviet Union."
Jimmy Hoffa, president of the Teamsters Union, and mobsters Carlos Marcello, Sam Giancana, Johnny Roselli, Charles Nicoletti, and Santo Trafficante Jr.—all of whom say Hoffa worked with the CIA on the Castro assassination plots—top the list of House Select Committee on Assassinations Mafia suspects.
It is also alleged that Mafia criminals may have wished to retaliate against John F. Kennedy in response to the increasing pressure put on them by Robert Kennedy, who had increased by 12 times the number of prosecutions conducted under the administration of President Dwight Eisenhower. Carlos Marcello allegedly threatened to assassinate the President to short-circuit Robert Kennedy, who was serving as US Attorney General and leading the administration's anti-Mafia crusade.
In his memoir, Bound by Honor, Bill Bonanno, son of New York Mafia boss Joseph Bonanno, disclosed that several Mafia families had long-standing ties with the anti-Castro Cubans through the Havana casinos operated by the Mafia before the Cuban Revolution. Many Cuban exiles and Mafia bosses disliked President Kennedy, blaming him for the failed Bay of Pigs Invasion. They also disliked his brother, the young and idealistic Attorney General Robert Kennedy, who had conducted an unprecedented legal assault on organized crime. This was especially provocative because several of the Mafia "families" had allegedly worked with JFK's father, Joseph Kennedy, to get JFK elected. Both the Mafia and the anti-Castro Cubans were experts in assassination, the Cubans having been trained by the CIA. Bonanno reported that he realized the degree of the involvement of other Mafia families when he witnessed Jack Ruby killing Oswald on television—the Bonannos recognized Jack Ruby as an associate of Chicago mobster Sam Giancana.
Information released around 2006 by the FBI indicates that Carlos Marcello confessed in detail to having organized Kennedy's assassination. The FBI then covered up this information, which it had in its possession. This version of events is supported by Robert Blakey in his book, The Plot to Kill the President. Blakey, who was chief counsel for the House Select Committee on Assassinations, concluded that Marcello was likely part of a Mafia conspiracy behind the assassination, and that the Mafia had the means, motive, and opportunity required to carry it out.
https://en.wikipedia.org/wiki/CIA_Kennedy_assassination_conspiracy_theory