Story highlights The 1964 killings of three civil rights workers galvanized the civil rights movement

Edgar Ray Killen was convicted of manslaughter and sentenced in 2005

(CNN) A Klansman found guilty for his role in the 1964 Freedom Summer killings of three civil rights workers has died in prison, according to the Mississippi Department of Corrections.

Edgar Ray Killen, a part-time Baptist minister and the plot leader, was convicted of three counts of manslaughter nearly 13 years ago.

Edgar Ray Killen was found guilty in 2005 of three counts of manslaughter.

Killen, who would have turned 93 on January 17, was pronounced dead Thursday night at the hospital of the Mississippi State Penitentiary, the department said. The cause and manner of death are pending an autopsy. However, no foul play is suspected, it said.

The slayings were among the most notorious of the civil rights era and were the subject of the 1988 movie "Mississippi Burning."

The killings of James Chaney, 21, Andrew Goodman, 20, and Michael Schwerner, 24, helped galvanize the civil rights movement that ushered in major reforms in access to voting, education and public accommodations.

Read More