Nine of the soldiers who declined to take the witness stand are among a dozen infantrymen of the 5th Stryker Brigade, based in Washington state, who are charged in a case stemming from their deployment in Afghanistan's Kandahar province.

The first soldier formally accused in the case, Army Specialist Jeremy Morlock, 22, is charged with premeditated murder in the deaths of three Afghan civilians, assaulting a fellow soldier and "wrongfully photographing and possessing visual images of human casualties."

In two of the slayings, fragmentary grenades were thrown at the victims and they were shot, according to charge sheets. The third victim also was shot.

Morlock, from Wasilla, Alaska, wore standard Army combat fatigues and sat silently during Monday's proceedings. He was not expected to testify. If found guilty of all the charges against him, Morlock, could face the death penalty.

He is the first to be brought before a military court for a so-called Article 32 hearing, in which prosecutors and defense lawyers present evidence to an investigating officer who decides whether there should be a formal court-martial.

The hearing at Joint Base Lewis-McChord near Tacoma, Washington, was expected to last a day, with the investigating officer taking up to several weeks to decide whether a court-martial was warranted, Army Maj. Kathleen Turner said.

Morlock's civilian lawyer, Michael Waddington, suggested in court that the defendant was under the influence of various prescription drugs when questioned by an investigator, Anderson Wagner, in May.

Wagner acknowledged knowing Morlock had been taking muscle relaxants, sleeping pills, pain killers and other medications at the time he was interviewing the defendant, but he insisted Morlock seemed "very articulate," was able to answer questions quickly, and did not seem impaired.

Four other US soldiers were charged in June with the same murders as Morlock, and seven additional servicemen have been charged since then with other crimes stemming from the investigation, including conspiracy to cover up the slayings.

Four of the soldiers are charged with keeping body parts, including finger bones, a skull, leg bones and a human tooth. Court documents say Morlock threatened a fellow soldier by showing him "fingers removed from a corpse."

The 5th Stryker Brigade soldiers deployed to Kandahar a year ago, and the slayings occurred between January and May, according to charges by army prosecutors.

The case threatens to become the most high-profile investigation of alleged crimes by US military personnel during almost nine years of war in Afghanistan.

Pentagon officials, while stressing the charges have yet to be proven, acknowledged the nature of the allegations was damaging to the image of the United States and its military around the world.