A 79-year-old man has pleaded "not guilty" in court to the notorious 1964 murders of three civil rights workers in the US state of Mississippi.
Killen is said to have been impassive and co-operative in court
Edgar Ray Killen, a segregationist preacher linked to the Ku Klux Klan, faced trial in 1967 but was freed after the jury failed to reach a verdict.
The three men were killed as they campaigned to register black voters.
The murders shocked many Americans and sparked an outpouring of support for the civil rights movement.
The story of the FBI investigation into the crime was dramatised in the 1988 film Mississippi Burning.
Mr Killen, who has always denied the murders, will reappear in court on Wednesday.
The case has proved divisive, says BBC correspondent Rob Watson, with victims' relatives welcoming what they see as belated justice and others arguing that the process will only open old wounds.
Neshoba County Sheriff Larry Myers said there would be further arrests in connection with the killings.
Beaten and shot
James Chaney, Michael Schwerner and Andrew Goodman were driving to investigate a fire at a church when they were allegedly stopped by Ku Klux Klansmen on an isolated road.
Chaney, 21, a black man from Meridian, Mississippi, was beaten to death. Schwerner, 24, and Goodman, 20, from New York, were shot in the chest.
Their bodies were found several weeks later, buried in an earthen dam, after one of the largest searches ever undertaken by the FBI.
Eighteen people were charged in 1967 on federal conspiracy charges, but none of them was charged with murder.
Seven people were convicted and served up to six years in prison.
Mr Killen was freed after his trial ended in a hung jury.
His arrest at his home in Philadelphia, Mississippi, followed a grand jury session on Thursday that apparently included testimony from people believed to have knowledge of the killings.
The mother of one of the victims welcomed the news.
"This has been a long time coming, but it was definitely worth the wait," Carolyn Goodman, the mother of Andrew Goodman, was quoted as saying.
"I knew in my heart this would happen eventually. It just had to be. I feel so relieved."