It was 40 years ago today that Robert F. Kennedy died after being gunned down in California. Much like his brother's death, the assassination remains a source of intrigue. As we mark the anniversary of this tragic event, a new documentary is raising questions about who may have been involved in RFK's murder.

Kennedy mysterious murder is the subject of a new documentary, RFK must die, The Assassination of Bobby Kennedy. Filmmaker Shane O'Sullivan uncovered new evidence that suggests the lone gunman Sirhan Sirhan, now serving a life sentence, didn't act alone.

O'Sullivan told CNN that a second gunman seems to have been behind RFK. O'Sullivan said, "There's new audio evidence of the only audio recording of shooting suggesting 13 shots were fired, eight from the front, Sirhan's position and five from the back, which is where this mysterious gunman seems to have been."

This video is from CNN's American Morning, broadcast June 6, 2008.

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