It is among the worst in a series of cases of alleged misconduct. Specialist Barker's signed statement was submitted in evidence. He is accused, along with Sergeant Paul Cortez, Private Jesse Spielman and Private Bryan Howard of rape and murder. Another soldier, Sergeant Anthony Yribe, is accused of failing to report the attack but is not alleged to have participated.

Former private, Steven Green, was discharged from the army for a "personality disorder" after the incident and was arrested in North Carolina in June on rape and murder charges. He has pleaded not guilty and is being held without bail.

Yesterday, Private Justin Watt testified that Private Howard told him, before the incident, that Private Green, Sergeant Cortez and Specialist Barker had planned to rape a girl, and Private Howard was to be the lookout. Another investigator, Michael Hood, told the hearing that he interviewed Private Spielman, who denied shooting or having sex with anyone. He was given a lie-detector test and passed.

According to Specialist Barker's statement, Private Green not only raped the girl but also shot her and her family after telling his comrades repeatedly he wanted to kill some Iraqis. Mr Bierce said that on the day of the attack, Specialist Barker, Sergeant Cortez, Private Spielman and Private Green had been playing cards and drinking Iraqi whisky mixed with an energy drink. They practised hitting golf balls, Specialist Barker's statement said.

Specialist Barker made it clear Private Green was very persistent about killing some Iraqis. At some point they decided to go to the house of the girl they had seen passing by their checkpoint. Specialist Barker also said that when they arrived at the house, the father and the girl were outside. Private Spielman grabbed the girl while Private Green seized her father and took them into the house.

Private Green took the father, mother and the younger sister into the bedroom, while the girl remained in the living room. Specialist Barker wrote that Sergeant Cortez pushed the girl to the floor, and tore off her underwear. Sergeant Cortez appeared to rape her, according to the statement. Specialist Barker then tried to rape the girl, Mr Bierce said. Suddenly, the group heard gunshots. Private Green came out of the bedroom holding an AK-47 rifle and declared: "They're all dead. I just killed them," the statement said.

Private Green put the gun down, then raped the girl while Sergeant Cortez held her down. Specialist Barker claims Private Green picked up the AK-47 and shot the girl once, paused, then shot her several more times. Specialist Barker said he got a lamp and poured kerosene on the girl. She was set on fire, but he does not say who did it. He does not say if Private Howard or Private Spielman took part in the rape. The statement says he grilled chicken wings back at their checkpoint.

The case has increased demands for changes to an agreement that exempts US soldiers from prosecution in Iraqi courts. Prime minister Nuri al-Maliki has demanded an independent investigation.