Specialist Charles Graner and three others are accused of sexually humiliating and, in some cases, beating Iraqi detainees at Iraq's notorious Abu Ghraib prison.
Photos of their tormenting of naked Iraqis aroused worldwide outrage when they emerged in April and sparked criticism that sweeping US "anti-terror" policies had encouraged the abuses.
Graner, who faces the most serious accusations and who featured prominently in the abuse photographs, was the first to appear at the pre-trial hearing at a US army base in Germany on Monday.
His lawyers argued that publicity surrounding events at Abu Ghraib meant it would be impossible to find an unbiased jury among Graner's peers.
Graner, in the background, faces
the most serious accusations
"While the prejudice would be worldwide, it is extremely acute in Baghdad as the feeling would be that he has hurt the mission," Captain Jay Heath, one of Graner's two lawyers, told the judge.
"There are some suggestions his actions have caused the death of some US soldiers," Heath added.
Graner's second lawyer, Guy Womack, later told reporters it would be almost impossible to persuade civilian witnesses to travel to Iraq.
"While I enjoy travelling to Iraq, most civilians would not, and US courts lack the authority to make them do so," he said.
Dressed in desert fatigues, Graner answered questions about the long hours in Iraq, sometimes 17 hours a day transferring detainees, and the stress of being under fire.
Graner's photos later appeared in
the Washington Post
"We worked every day... Several of our platoon had taken fire. Both my roommates had been injured, took blasts... It was one of the most stressful times," Graner said.
Earlier, a military investigator referred to CDs of hundreds of pictures, taken from Graner's room during a search in January, depicting the abuse of detainees.
Graner's lawyers said the photographs were taken without his full consent, but Judge James Pohl dismissed a motion to strike the potentially incriminating images from his court martial.
Graner, 35, is accused of photographing a detainee being dragged by Private First Class Lynndie England on a leash, and posing for a picture by a pile of naked detainees in November.
He is also said to have forced prisoners to strip naked and masturbate in front of each other, and one to simulate oral sex on another, before taking pictures.
Graner is also charged with committing adultery, an offence against military discipline.
"We worked every day... Several of our platoon had taken fire. Both my roommates had been injured, took blasts... It was one of the most stressful times"
Specialist Charles Graner,
accused Abu Ghraib abuser
Defence lawyers for the accused - Specialists Graner and Megan Ambuhl, Staff Sergeant Ivan Frederick and Sergeant Javal Davis - argue their clients were following orders to systematically break inmates for interrogation.
US officials say the accused were wayward individuals and their actions isolated ones.
At an initial hearing in Baghdad in June, Graner's lawyer said US President George Bush and Defence Secretary Donald Rumsfeld should take the witness stand.
Davis's lawyers are set to bring a motion compelling Rumsfeld to testify.
The Mannheim hearings are expected to last two days.