District Attorney Mark Duncan said he is not surprised the U.S. Supreme Court on Monday rejected an appeal from Edgar Ray Killen, convicted of manslaughter in 2005 for the 1964 slayings of three civil rights workers in Neshoba County in what became known as the "Mississippi Burning" case.

"He has appealed to every court we have and lost every time," Duncan said.

The decision means the justices won't review lower-court rulings that found no violations of Killen's constitutional rights during his trial in Mississippi.

Killen, now 88, a former sawmill operator and one-time Baptist preacher, was convicted of manslaughter on June 21, 2005, 41 years to the day after the deaths of Michael Schwerner, James Chaney and Andrew Goodman. He is serving 60 years in a Mississippi prison.

In 1964, Schwerner and Goodman, two white men from New York, came to Mississippi as part of Freedom Summer and teamed up with Chaney, a young black Mississippian, to help register black voters. They were ambushed by members of the Klan in Neshoba County and killed before being buried in an earthen dam. Their bodies were found weeks later after an intense search.

The deaths were dramatized in the 1988 movie ``Mississippi Burning.'

On Monday, his attorney, Rob Ratliff of Mobile, told The Clarion-Ledger that he vowed to keep fighting, saying the "legal options are not over. Several other options exist in the course of having proper judicial review of a conviction and sentencing that failed to meet our respected standards."

Justices were not asked to rule on substantive issues, but to recognize Killen's constitutional right to due process, Ratliff wrote in an email to the Jackson newspaper.

"The Court was severely limited in its time and resources to properly digest the questions posed in Mr. Killen's petition," he wrote. "The literally hundreds of petitions disposed of this week by the Supreme Court indicates that important constitutional issues impacting rights of liberty and justice may not be given their proper review."

Killen's lawyers raised several arguments in his appeals, including that his defense team didn't do a good job in representing him at trial in Neshoba County.

They also argued that his constitutional rights were violated by the decades-long delay between the deaths and his indictment, by variances between the charges in the indictment and the jury's verdict, and by prosecutors' alleged failure to turn over evidence that could prove his innocence.

U.S. District Judge Henry T. Wingate in Jackson, Miss., and the 5th U.S. Circuit Court of Appeals both rejected Killen's appeals before the case went to the U.S. Supreme Court.

In 1967, seven men were convicted of federal charges of violating the civil rights of the men killed.

None served more than six years in prison. The trial for Killen on the federal charges ended in a hung jury.

Killen, once a part-time preacher, was the only person indicted in 2005 when prosecutors brought the first state charges. He was indicted on murder charges but jurors were given the option to convict him of manslaughter, which they did.