Robert Kennedy Jnr has told ITV News that his father's first instinct after JFK was shot was to wonder whether the CIA was involved.
Robert Kennedy Snr asked then CIA Director John McCone about it but was reassured that it wasn't the case.
However Kennedy Snr - JFK's brother - always felt Lee Harvey Oswald didn't act alone.
Robert Kennedy Jnr also revealed how the surviving family members will mark the 50th anniversary of the assassination.
He said they prefer to celebrate his birthday and the good times in JFK's life.
"The endless replays of the assassination tapes are hard to take," he told our Washington Correspondent Robert Moore.
As the world remembers the assassination of John F. Kennedy, many are reviewing his final day and the evidence around his murder.
President Kennedy's assassination left America permanently scarred.
Half a century since the murder of President John F Kennedy in Dallas, America pauses to remember their fallen hero.