Robert F Kennedy Jnr is convinced a lone gunman was not solely responsible for the assassination of his uncle, John F Kennedy, and said his father was disparaging about the official report into the killing.
Mr Kennedy and his sister Rory, a documentary film-maker, were being interviewed in front of an audience at the Winspear Opera House in Dallas on Friday. The event was one of many planned in the run-up to the 50th anniversary of the president's death. Their uncle was killed on 22 November 1963, while riding in a motorcade through Dallas. Five years later, their father was assassinated in Los Angeles.
Mr Kennedy said his father spent a year trying to come to grips with his brother's death, reading the works of Greek philosophers, Catholic scholars, Henry David Thoreau, poets and others, "trying to figure out kind of the existential implications of why a just God would allow injustice to happen of the magnitude he was seeing".
He added that his father thought the Warren Commission, which concluded that Lee Harvey Oswald acted alone in the assassination, was a "shoddy piece of craftsmanship". He said that he, too, questioned the report. "The evidence at this point, I think, is very, very convincing that it was not a lone gunman," but he didn't say what he believed might have happened.
Mr Kennedy said his father's investigators 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 was "fairly convinced" that others were involved.