On November 24, 1963, Lee Harvey Oswald was being moved to a different prison when he was shot and killed by Jack Ruby. Oswald's unexpected death has sparked conspiracy theories, including him being tied to the mob through Jack Ruby. Jack Ruby claimed to have murdered Lee Harvey Oswald impulsively out of grief and because he didn't want Jackie Kennedy to have to return to Dallas for a trial. To some, Ruby is seen as a hero for killing Kennedy's assassin, but others were angry Oswald was shot because he never testified. Since Oswald died so shortly after the assassination, investigators don't know a lot of information about his motives. Some conspiracists believe Ruby killed Oswald to cover him from revealing names or the details for a huge plan to assassinate Kennedy. Given Ruby's ties to mob leaders, this theory is plausible. Therefore, Jack Ruby most likely assassinated Oswald in order to prevent him from ever revealing his motives.
It cannot be confirmed that Jack Ruby was working with the mafia at the time of Kennedy's assassination. He was known to have minor ties to the mob previously due to owning multiple strip clubs and dance halls in Dallas. Additionally, Ruby officially testified to have shot Oswald because he was overwhelmed with grief for the Kennedy family, and not as part of a larger cover up. It cannot be confirmed that the mafia had any connections to JFK's assassination.
[P1] Jack Ruby assassinated Lee Harvey Oswald. [P2] Because Oswald was killed, he never revealed his motives for assassinating JFK. [P3] Jack Ruby killed Oswald so he wouldn't reveal his motives. [P4] Jack Ruby has ties to the mob. [P5] Therefore, the mob killed JFK.
Rejecting the premises
[Rejecting P3] Jack Ruby claimed to kill Oswald because he was grieving.