The body of John Boncore, 61, was found March 13 in his home on the Adams Lake Indian Reserve in British Columbia, Barb McLintock of the B.C. Coroners Service said Monday.
He reportedly had fallen earlier nearby, she said, but the cause of death has yet to be released because the investigation is ongoing.
"There is nothing to suggest foul play," she said.
The death was reported last month in local B.C. media.
Boncore, a Mohawk Indian who was born in Buffalo, was known as John B. Hill at Attica when inmates took control of the maximum-security prison in rural western New York.
Thirty-two inmates and 11 civilian employees died during the five-day siege, including 10 hostages and 29 inmates who died when state troopers stormed the prison's D Yard on Sept. 13, 1971.
In 1975, a state Supreme Court jury in Buffalo convicted Boncore of murder in the beating death of Corrections Officer William Quinn. He was sentenced to at least 20 years in prison.
Boncore, who had denied attacking Quinn with a piece of wood as alleged, was granted clemency in 1976 by then-governor Hugh Carey, who also freed seven other inmates convicted of crimes during the riot and dismissed pending disciplinary actions against 20 law enforcement officers.
Following his release from prison, Boncore became active in several causes and eventually moved to Canada.
Boncore — who often used his aboriginal name Splitting the Sky — was arrested in 2009 when he tried to break through a barricade of Calgary police officers to get inside a building where U.S. president George W. Bush was delivering a speech.
Boncore was with a group of activists who were protesting the paid appearance by the former president, who they accused of war crimes in Afghanistan and Iraq.
He was found guilty of obstructing a peace officer but was released with a conditional discharge was ordered to pay $1,000 to a charity of his choice.
After the trial, Boncore told reporters he stood by his actions.
"I'm not so sure if I'll make a citizen's arrest, but you can believe wherever George Bush (and his former cabinet colleagues) ... wherever they come I will be there to voice my opposition,'' he said.
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