I suggested that the new story that "the Saudis did 9/11" was put into play to take the place of the worn and battered first cover story. http://www.paulcraigroberts.org/2016/07/20/is-the-saudi-911-story-part-of-the-deception-paul-craig-roberts/
When the Oswald cover story for JFK's assassination came under heavy suspicion http://www.paulcraigroberts.org/2017/05/24/jfk-100-paul-craig-roberts/, other cover stories appeared in the media. One was that the Mafia killed JFK, because he was having affairs with their molls.
The fact that it made no sense did not stop many from believing it. It did not occur to people more gullible than thoughtful that a gangster would simply get another woman and not take the risk of assassinating the US president over a woman. The last thing the Mafia would want would be for Attorney General Robert Kennedy to bring the law down on the Mafia like a ton of bricks.