CAMP PENDLETON -- A Marine sergeant charged with killing a detainee in Iraq headed to jail Wednesday after refusing to testify against a war comrade accused in the same incident, the sergeant's attorney said Thursday.

The detention came to light when Sgt. Jermaine Nelson failed to show up in a Camp Pendleton courtroom Thursday morning, where he was to be arraigned on charges of unpremeditated murder and dereliction of duty.

U.S. District Judge Percy Anderson ordered Nelson, 26, to jail after the sergeant refused to testify before a federal grand jury investigating his buddy, Jose Nazario Jr., according to Nelson's civilian attorney, Joseph Low.

"My client said, 'Sgt. Nazario saved my life on a number of occasions, and I'm not going to testify,' " said Low, who spoke outside of court after Nelson's arraignment was put on hold while the matter is sorted out.

Thom Mrozek, spokesman for the U.S. attorney's office in Los Angeles, confirmed that Nelson had been jailed for contempt of court, but could offer no additional information.

"The documents related to that hearing, that resulted in the contempt finding, are filed under seal," Mrozek said.

Grand jury proceedings are secret.

Nazario, Nelson and a third man -- all of whom were Camp Pendleton Marines -- stand accused in the shooting deaths of four detainees in November 2004 during fierce fighting in Fallujah.

At the time, all three men were squad members from Camp Pendleton's 3rd Battalion, 1st Marine Regiment, 1st Marine Division.

Also charged in military court for the incident is a third man, 25-year-old Ryan Weemer, who allegedly revealed the incident while interviewing for a job with the Secret Service.

Weemer was charged with one count of unpremeditated murder, a charge akin to second-degree murder in the civilian justice system.

The cases are the latest in a number of high-profile war crimes accusations involving Camp Pendleton Marines since the start of the Iraq war five years ago.

Nazario, 27, had left the Marine Corps and was a probationary Riverside police officer when he was charged. His case is in a federal civilian court because he is no longer an active-duty Marine.

His attorney, Kevin McDermott, said Thursday that the prosecutor, Assistant U.S. Attorney Jerry Behnke, is seeking a federal grand jury indictment against Nazario.

Nazario, who is not in jail, has already been charged with voluntary manslaughter and is scheduled for trial in July. McDermott said he believes prosecutor Behnke wants to toughen the charges to murder, and that is why he has taken the matter to a grand jury.

Behnke did not immediately return a call for comment Thursday.

Attorney Low said Nelson made it clear that he does not intend to testify against his comrade.

"Sgt. Nelson got down on his knee, put his head between his hands and prayed," Low said, adding that his client then rose and said he would rather go to jail than testify.

"Now he's doing time for somebody who is not even in custody," Low said.

Low said Nelson opted for jail in spite of the government's offer of a limited type of immunity.

It is unclear when Nelson could be released if he continues to refuse to testify. Low said he could remain jailed until the grand jury finishes its term, which is set for December.

Contact staff writer Teri Figueroa at (760) 740-5442 or tfigueroa@nctimes.com.