Reputed Klansman Edgar Ray Killen has pleaded innocent to the 1964 murders of three civil rights workers in Mississippi.

Killen entered his plea in a Philadelphia, Miss., courtroom Friday while handcuffed and dressed in an orange jail jumpsuit. Three times, he responded loudly with the words "not guilty."

Soon after the arraignment, the courthouse was cleared by authorities who said they had received a bomb threat. There's no word on whether a device was found.

This is the first time state authorities have sought criminal charges in the case.

Killen is charged in the shooting deaths of James Chaney, Andrew Goodman and Michael Schwerner in a rural area. Their bodies were eventually recovered from a makeshift grave.