The cause and manner of death were pending an autopsy, the statement said. No foul play was suspected.
Killen, whose 2005 manslaughter conviction came on the 41st anniversary of the crime, was serving a 60-year prison sentence – the maximum 20 years for each victim. In a 2015 interview with the Associated Press, Killen refused to discuss his case but said he was still a segregationist, although he had no ill will for blacks.
The slayings of James Chaney, Andrew Goodman and Michael Schwerner in Philadelphia, Mississippi, on June 21, 1964, at the hands of the Klan, local law enforcement officers and others was one of the most shocking and galvanizing moments of the U.S. civil rights movement.