Officials and family members say 81-year-old Edgar Ray Killen has been hospitalized for complications from a severe leg injury he sustained in a logging accident.
Killen was transported from prison to the University of Mississippi Medical Center, where a spokeswoman said he was in fair condition as of Tuesday night.
A tree fell on Killen while he was cutting wood March 10, 2005, near his Union, Miss., home, just months before he was convicted of three counts of manslaughter in the slayings of James Chaney, Michael Schwerner and Andrew Goodman.
The tree knocked Killen out and shattered the bones in both of his thighs. He spent the trial confined to wheelchair.
A 1967 federal trial found that the murders of Goodman, Chaney and Schwerner were part of a Ku Klux Klan conspiracy. Killen's case ended in a hung jury, but seven others were convicted of violating the victims' civil rights. None served more than six years.
Killen is the only person to face state charges in the case that helped focus national attention on the civil rights struggle in the South and was dramatized in the 1988 movie "Mississippi Burning."