Like every other presidential assassination or attempted presidential assassination in American history except Lincoln (whose conspiracy was revealed immediately and in a very obvious way), Kennedy was killed by one person acting alone, and that person was Lee Oswald
No he wasn't Jack Ruby was part of the Mafia as well we call it Pinkerton Conspiracy of the Crime if someone is suspected of committed of murder but can't pin it directly on him but we can pin the conspiracy of the crime
Jack Ruby knew Oswald and they were both part of the Mafia and so was Hoffa and Frank Sinatra
The Mafia with Scareface was involved in Ronald Reagan assassination attempt, he was involved with Frank Sinatra, its a reason he didn't get killed the Mafia liked Reagan
Kevin Costner said it was impossible for JFK head to explode from that angle of a shot