I believe that it was Oswald who killed JFK, but it was Jack Ruby, the man who killed Oswald, who hired him to do the deed.

There is some weight to the theory of mafia involvement in JFK's murder — but with no absolutely concrete evidence, it's hard to know for sure.

JFK was shot dead from his motorcade in Dallas in November 1963. Harvey Lee Oswald was arrested 90 mins later — he denied the shooting, claiming to be a 'patsy'. The following day, Oswald was shot on national TV by [Jack Ruby] (https://crimereads.com/kennedy-assassination-theories-jack-ruby/). Ruby was a nightclub owner with links to organised crime who claimed to have loved JFK and to have been avenging his murder.
The theory goes that Oswald was the fall guy and that Ruby may have owed a debt to the mob which meant he got the job of making sure Oswald was silenced.

Why would the mafia want to get rid of JFK?

• Kennedy's bungling of the [Bay of Pigs operation] (https://www.historyextra.com/period/20th-century/bay-of-pigs-invasion-kennedys-cuban-catastrophe/) & failure to take down Fidel Castro meant that mafia-owned casinos in Cuba remained shut down & reaped no profits.
• JFK's brother [Robert Kennedy] (https://www.history.com/news/robert-kennedy-started-the-war-on-mafia-gangs) constantly campaigned against mafia influence and organised crime — murdering the president could have had the motivation of toppling a leadership that seemed bent against them.

The evidence for mafia involvement:

• Investigations into JFK's murder [were contradictory] (https://en.wikipedia.org/wiki/John_F._Kennedy_assassination_conspiracy_theories). In 1964, a commission concluded that Oswald had acted alone. Then in 1979, the HSCA claimed that JFK's death had been part of a conspiracy, although they did not divulge more info.
• In 2017, [some classified files] (https://www.history.co.uk/article/did-the-mob-kill-jfk-new-evidence-suggests-they-did) were released by the US government which seemed to place Ruby at the scene of the shooting — despite previous evidence that he had been 5 blocks away at the time.
• The commission into JFK's death included an interview with Ruby in 1964, in which he claimed to be in danger — but with no more specificity. He died in 1967 of natural causes without revealing whatever he might have known.

Maybe one day, with the [eventual release] (https://www.nytimes.com/2021/10/23/us/politics/jfk-assassination-pandemic.html) of more highly classified government documents, we'll know for sure whether JFK's murder was part of a mafia plot. For now — there is ample evidence to support the theory, but nothing that proves it beyond doubt. Hence it is a conspiracy theory, not something to be taken as a verifiable fact.