Robert F Kennedy Jr has said he doesn't believe that a lone gunman was the only one responsible for the 1963 assassination of his uncle, President John F Kennedy. 

Robert F Kennedy Jr and his sister, Rory,  were interviewed by Charlie Rose in front of an audience at the Winspear Opera House in Dallas, where a year of observances begins for the 50th anniversary of JFK's death.

Five years after the president was killed, their father was assassinated in a hotel in Los Angeles while celebrating his win in the California Democratic presidential primary.

According to the Associated Press, Robert F Kennedy Jr said his father  believed the Warren Commission report, which concluded Lee Harvey acted alone in killing the president, was a "shoddy piece of craftsmanship."

"The evidence at this point I think is very, very convincing that it was not a lone gunman," Kennedy told Rose, although he didn’t go on to say what he thinks may have happened.

Rose asked Kennedy if he believed his father, who was the U.S. attorney general at the time of the president's assassination, felt "some sense of guilt because he thought there might have been a link between his very aggressive efforts against organized crime."

Said Kennedy: "I think that’s true. He talked about that. He publicly supported the Warren Commission report but privately he was dismissive of it."

He went on to say that an investigation spearheaded by his father found that phone records of Oswald and nightclub owner Jack Ruby, who killed Oswald two days after the president’s assassination, ‘‘were like an inventory’’ of mafia leaders the government had been investigating.

He said his father, who would later be elected U.S. senator in New York, was "fairly convinced" that others were involved.

Rory Kennedy, a documentary filmmaker, told Rose: "In all of the tragedy and challenge, when you try to make sense of it and understand it, it’s very difficult to fully make sense of it. But I do feel that in everything that I've experienced that has been difficult and that has been hard and that has been loss, that I've gained something in it."

Her brother added: "We were kind of lucky because we lost our members of our family when they were involved in a great endeavor. And that endeavor is to make this country live up to her ideals."

Fifty years after President Kennedy’s shocking assassination, Detective Jim Leavelle has been honored by Dallas PoliceGoogle Images