Robert F. Kennedy, the Attorney General and President Kennedy's younger brother, never did believe the Warren Commission despite his public refusal to contradict the official version of events.
The younger Kennedy began his own investigation the day of the murder convinced that members of the U.S. government were responsible for the shooting in Dallas. Author David Talbot perhaps sums it up best in his book Brothers. "Robert Kennedy did not resign himself to the lone gunman theory. On the contrary, he immediately suspected that President Kennedy was the victim of a powerful conspiracy. And he spent the rest of his life secretly searching for the truth about his brother's murder."