The Hollywood actor narrated the film Incident at Oglala, which focused on the killing of two Federal Bureau of Investigation (FBI) agents at an Indian reservation in South Dakota in 1975.

Peltier is serving a life sentence for the murders, but many believe he is innocent as another man, Robert Robideau, who was acquitted of the shootings at trial, is said to have confessed prior to his death in 2009.

The 70 year old is now in failing health, so Redford has made a fresh appeal for Peltier's release and urged U.S. President Barack Obama to grant him an official pardon.

Speaking on U.S. TV show Sunday Edition, Redford says, "I felt that he did not receive a fair trial... I am very hopeful (that Obama will issue a pardon) and will raise my voice in any way."