My Own Conspiracy Theory

Lee Harvey Oswald lusted for attention and fame. From taking a trip to the Soviet Union as a defecting Marine to a failed assassination attempt of Edwin Walker, Oswald seemed to want to stir up trouble. Evidence supporting his disappointment of not making the news on his return to the U.S. from the Soviet Union is cited as source 69 of this article.

My theory is that Oswald met Jack Ruby (who assassinated him two days after JFK's death) in New Orleans sometime between September 11, 1959 (when Oswald was discharged from the Marines based on his request) and his emigration to the Soviet Union. At the time, Ruby was pro-Cuba and was running guns to Castro's forces (source). Further evidence that Ruby knew or knew of Oswald is evident in this excerpt, which cites credulous sources including the Warren hearing and FBI documents. Clearly, Ruby knows that Oswald is pro-Cuba, so he must have had some sort of connection or knowledge of the man. According to the second article in this link, Ruby evidently made Mafia connections while in New Orleans. Obviously, since the gun-running was a Mafia operation, this makes sense. Also, since Ruby's trip to Cuba took place in August, the meeting between Oswald and Ruby is chronologically possible as Ruby would be back in New Orleans by September 11. Ruby also had police connections (source). Furthermore, Ruby had longtime ties with influential mobster Joseph Camisi in Dallas (source) who had direct ties to Carlos Marcello.

Carlos Marcello was Louisiana's Mafia Godfather during the entire assassination incident. Marcello had beef with the Kennedys because the Kennedy brothers served on the committee that investigated him for organized crime in 1959 (source). He hated the Kennedys, and donated $500,000 to Nixon's campaign in 1960 in hopes Kennedy would not be elected.

1963 was when all the stars lined up.
My mindset is that Marcello found out that Kennedy was travelling to Dallas, and had enough time to reach out to his Mafioso contacts in Dallas. This contact happened to be Campisi, whom we have already established had longtime connections to Ruby (source). The night before Kennedy's assassination, Ruby dined with Campisi at his restaurant (source). Ruby would then scout the path the president would take and realized he had a connection, Oswald, who worked nearby. Since Oswald was a sharpshooter in the Marines, he was the ideal gunman. Ruby, through his police connections, arranged a second shooter on ground level, making sure there were no policeman nearby. Ruby himself may have been the grassy knoll shooter. Oswald did say he was a scapegoat (source), and his assassination solidifies his position as the primary suspect, even though the bullet's entry at the forehead of JFK as well as the obviously planted pristine bullet points to the grassy knoll shooter as the actual assassin. There is simply too much suspicious, altered evidence that makes Oswald seem guiltier than he actually was. The Mafia would rather have Oswald, who had barely any ties to the Mafia, be the primary suspect. That said, Oswald did fire shots in Kennedy's direction, so he is a guilty scapegoat. His role was to draw guilt away from Ruby and the Mafia. JFK's corpse was modified to conceal the fact that the lethal bullet came from the front.

Ruby admitted to being part of a party of a plot to "silence Oswald" (source). He also said to Warren that "I want to tell the truth, and I can't tell it here" (source). Furthermore, "Gail Raven", a close acquaintance of Ruby also claimed that he had "no other choice" than to assassinate Oswald, clearly indicating an external pressure (Hint: the Mafia) (source).
But why did the Mafia feel the need to silence Oswald? As mentioned in paragraph one, Oswald craved media attention. Furthermore, Oswald was not very trusted my the Mafia, as he was more of a contract killer than a longtime Mafia member like Ruby was. Thus, the Mafia would have made threats to Ruby and his family if he did not "silence" Oswald, either using his police connections or assassinating Oswald himself.
Lastly, both Oswald and the grassy knoll shooter (probably Ruby) were equally guilty. However, the Mafia used Oswald as a scapegoat to avoid suspicion.

From this, we deduce that Jack Ruby was keystone in organizing the assassination, being in the right place at the right time, with all the right connections.