John Boncore had also gained notoriety 38 years later when he tried to make a ''citizen arrest'' of former U.S. president George W. Bush in Calgary.
The body of the 61-year-old former inmate was found March 13 in his home on the Adams Lake Indian Reserve in British Columbia.
The coroner‘s office says Boncore‘s death was caused by a life-threatening blood alcohol level of 0.35 per cent, recent cocaine use and an enlarged heart.
Boncore, a Mohawk Indian born in Buffalo, N.Y., was known as John B. Hill at Attica when inmates took control of the maximum-security prison in 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.
After leaving prison, Boncore — who often used his aboriginal name Splitting the Sky — became active in several causes and eventually moved to Canada.
Boncore was arrested in 2009 when he tried to break through a barricade of Calgary police officers to get inside a building where Bush was delivering a speech.
Boncore was with 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.
The coroner's report said witnesses saw Boncore purchase 24 beers throughout the day on March 11. He was last seen alive that night when a taxi drove him home from a known drug house, the report said.
The taxi driver reported Boncore fell down the steps to his basement apartment, but said he was fine and went inside. The autopsy, which concluded Boncore died early on March 12, showed no significant injury and no sign of foul play.
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