The FBI has publicly released files and photographs from the 1964 murder case that inspired the film "Mississippi Burning" and helped propel the passage of the 1964 Civil Rights Act.

The never-before-seen files lay out the investigation into the murders of Freedom Summer civil rights workers James Chaney, 22, Michael Schwerner, 24, and Andrew Goodman, 20, by the Ku Klux Klan. The bodies of the missing activists were found buried in a partially constructed dam near Philadelphia, Mississippi on Aug. 4, 1964.

The FBI website says, “The murders galvanized the nation and provided impetus for the passage of the landmark Civil Rights Act of 1964.”

CBS News reports that the previously sealed materials are available for viewing at the William F. Winter Archives and History Building in Jackson, Miss. The materials include case files, research notes, witness testimonies, and photographs of the victims’ autopsies and the burial site, according to the Mississippi Department of Archives and History.

RELATED: This Day in Black History: Aug. 4, 1964

Chaney, Schwerner, and Goodman were members of the Congress of Racial Equality (CORE) taking part in the Freedom Summer voter registration campaign. The three were investigating the burning of a Black church near Philadelphia, MS, when they disappeared. The FBI found that they were arrested by a deputy sheriff on a traffic charge, who then released them after alerting members of the KKK.

Seven of 18 defendants in the case, including a deputy sheriff, were found guilty in October 1967. None of the seven were found guilty on murder charges, and none of the guilty served more than six years in prison.

In 2005 the case was reopened and a Mississippi jury convicted Edgar Ray Killen, a 1960s Ku Klux Klan leader and Baptist minister, on three counts of manslaughter. Witnesses said that Killen, who went free in the 1967 trial, gathered the mob of Klansmen and directed the killings. Killen was sentenced to three consecutive terms of 20 years in prison, where he died in 2018.