DALLAS -- Robert F. Kennedy Jr. is convinced that a lone gunman wasn't solely responsible for the assassination of his uncle, President John F. Kennedy, and said his father believed the Warren Commission report was a "shoddy piece of craftsmanship."

Kennedy and his sister, Rory, spoke about their family Friday night while being interviewed in front of an audience by Charlie Rose at the Winspear Opera House in Dallas. The event comes as a year of observances begins for the 50th anniversary of the president's death.

Their uncle was killed on Nov. 22, 1963, while riding in a motorcade through Dallas. Five years later, their father was assassinated in a Los Angeles hotel while celebrating his win in the California Democratic presidential primary.

Robert F. Kennedy Jr. said his father spent a year trying to come to grips with his brother's death, reading the work 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 said his father thought the Warren Commission, which concluded Lee Harvey Oswald acted alone in killing the president, 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," he said, but he didn't say what he believed may have happened.

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

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

He said his father had investigators do research into the assassination and 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, later elected U.S. senator in New York, was "fairly convinced" that others were involved.

The attorney and well-known environmentalist also told the audience light-hearted stories Friday about memories of his uncle. As a young child with an interest in the environment, he said, he made an appointment with his uncle to speak with him in the Oval Office about pollution.

He'd even caught a salamander to present to the president, which unfortunately died before the meeting.

"He kept saying to me, `It doesn't look well,'" he recalled.

Rory Kennedy, a documentary filmmaker whose recent film "Ethel" looks at the life of her mother, also focused on the happier memories. She said she and her siblings grew up in a culture where it was important to give back.

"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," she said. "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."

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

Related on HuffPost:

Loading Slideshow...
  • John F. Kennedy

    President John F. Kennedy speaks at a press conference on August 1, 1963. (Photo by National Archive/Newsmakers)

  • Husband And Wife

    A photo dated in the 1950s shows John F. Kennedy with his wife Jacqueline Bouvier Kennedy. (AFP/AFP/Getty Images)

  • Youth Movement

    John Fitzgerald Kennedy is pictured here in this 1960s White House photo. He was the first Catholic, and the youngest person, to be elected as president of the United States (AFP/Getty Images).

  • Happy Family

    U.S. Senator John Fitzgerald Kennedy (JFK) and his wife Jacqueline pose with their son John Jr. on December 10, 1960. (AFP/Getty Images)

  • Oath Of Office

    John F. Kennedy takes the Oath of Office for President of the United States in January 1961. (Photo by National Archive/Newsmakers)

  • Presidential Ticket

    An unlocated photo shows U.S. President John F. Kennedy (R) chatting with Vice President Lyndon B. Johnson in the early 1960s. (AFP/AFP/Getty Images)

  • Presidential Get-Together

    U.S. President John Fitzgerald Kennedy (L) meets in January 1961 at the White House, with former U.S. President Harry S. Truman (1884-1972). (AFP/AFP/Getty Images)

  • At The Podium

    John Fitzgerald Kennedy delivers a speech at the Waldorf Astoria hotel in New York city, 29 April 1961.

  • By His Side

    President John F. Kennedy speaks during a press conference as First Lady Jackie Kennedy looks on April 9, 1963 at the White House.

  • Facing The Press

    President John F. Kennedy arrives for a press conference on August 30, 1961 in Washington.

  • Making Choices

    U.S. President John Fitzgerald Kennedy signs the order of naval blockade of Cuba, on October 24, 1962 in the White House, during the Cuban Missile Crisis. (AFP/Getty Images)

  • Family Fun

    John Kennedy Jr. plays in the Oval Office at the White House, Washington, DC, on October 15, 1963.