16. The Mob
The reason this theory has gained so much traction over the years probably revolves around the fact that nightclub owner Jack Ruby, who confessed to the slaying of Lee Harvey Oswald, had well known connections with the Mafia and that this same man conveniently killed a presidential assassin a mere two days after the fact, before he could say even a word. This is another theory that takes many forms. Some say that Oswald was merely a patsy to a professional hit man and was killed by Ruby before he could talk. Others say that he was paid off by the mob to pull off the hit and was killed before he could rat out his superiors. Until the day he died in jail, however, Ruby insisted that his motivation for killing Oswald was out of vengeance and peace for the widowed First Lady.