Jack Ruby’s testimony to the Warren Commission.
Since Oliver Stone’s propagandistic movie JFK, many people have simply accepted a certain egregiously false notion that the movie presented as fact. In the movie, Jack Ruby wants to tell the Warren Commission who really murdered President Kennedy. Chief Justice Earl Warren prevents Ruby from so testifying. This is fabrication.
Jack Ruby told the Warren Commission he was not part of any plot to kill Kennedy, or any plot to keep Oswald from talking. (*) Jack Ruby was Jewish. After he shot Lee Harvey Oswald, some right-wing groups spread the story that Jack Ruby was part of a conspiracy to kill Kennedy. These claims were fabricated, motivated in part by anti-Semitism. Ruby caught wind of the charges. He was afraid that if someone believed that he, Ruby, had been part of a conspiracy, his life and the lives of his family would be at risk. Ruby demanded to take a lie detector test to prove he had no connection to any plot to silence Oswald.
At one point, in the actual hearings, when Ruby is explaining to the commission why he is afraid for his life, Chief Justice Earl Warren says that he would allow Ruby to refrain from further testifying, if he felt that way. Ruby, however, continued to testify. (†) Mirror
All of the evidence suggests that Jack Ruby acted alone and independent of anyone else.