Although there have been many studies of the trial of Louis Riel, following the 1885 rebellion, much less attention has been paid to the fate of his secretary William Henry Jackson, who was charged with “treason-felony” and found not guilty, reason of insanity. In an effort to throw some new light on this neglected aspect of medico-legal history, this paper describes the intense political and religious relationship between Riel and his secretary which culminated in the onset of Jackson's mental illness. After a trial lasting less than half an hour, Jackson was committed to the “Selkirk Asylum” under a warrant of the then Lieutenant-Governor. Two weeks before Riel was executed, Jackson escaped from hospital and made his way into the U.S.A. No attempt was made to capture him. Jackson, having changed his name to Honoré Jaxon, became a labour organizer. He died in the psychopathic ward of Bellevue Hospital in New York on 10th January, 1952 at the age of ninety.