A military judge said today that the top United States military commander in Iraq could be questioned during the trial of three American soldiers accused of torturing Iraqi prisoners at Abu Ghraib prison.

The move to question Lieutenant General Ricardo Sanchez is likely to have been informed by the three defendants' claims that the cruel and sadistic behaviour at the notorious prison was sanctioned from above and was not an isolated incident.

The defence lawyers will have their opportunity to interview General Sanchez and other senior officials before reporting back to the judge by July 31. The transcript of the interview would be made public and used in evidence during the proceedings, which may lead to a court martial.

But the judge, Colonel James Pohl, turned down a request from defence lawyers to question Donald Rumseld, the United States Defense Secretary, over the abuse.

Pre-trial hearings for three of the seven soldiers charged in the abuse scandal opened today in the heavily fortified Green Zone of Baghdad. Colonel Pohl was hearing motions in the cases against Sergeant Javal Davis, Specialist Charles A. Graner Jr and Staff Sergeant Ivan L. "Chip" Frederick II.

Colonel Pohl declared Abu Ghraib prison a crime scene during today's pre-trial hearing and ordered that it should not be destroyed, a move George W. Bush had suggested. Colonel Pohl also refused to move the case from Iraq as Sergeant Davis's lawyer had requested.

President Bush had offered to tear down Abu Ghraib and build a new prison to eliminate the legacy of torture and abuse which the facility developed during Saddam Hussein's rule and later because of the current scandal. Iraqi officials showed no interest in the offer, and the interim President, Ghazi al-Yawer, said destroying the facility would be a needless waste of resources.

On May 19, Specialist Jeremy C. Sivits became the first soldier convicted and sentenced in the scandal. Sivits pleaded guilty and received the maximum penalty of one year in prison, forfeiture of pay, reduction in rank to private and a bad conduct discharge.

The three defendants who appeared in court today face more serious charges and could receive long prison terms.

Specialist Graner, of Uniontown, Pennsylvania, has been accused of striking several detainees by jumping on them as they piled on the floor. He is also charged with stamping on the hands and bare feet of several prisoners and punching one inmate in the temple so hard that he lost consciousness. He also faces adultery charges for having sex with Lynndie England, another soldier charged in the scandal last October. He could receive 24 and-a-half years in jail, forfeiture of pay, reduction in rank, and a dishonourable discharge.

Staff Sergeant Frederick, of Buckingham, Virginia, is accused of forcing prisoners to masturbate, placing naked detainees into a human pyramid and placing wires on a detainee's hands, telling him he would be electrocuted if he fell off a box on which he was forced to stand. He faces a maximum punishment of 16 and-a-half years in confinement, forfeiture of pay, reduction of rank, and a dishonourable discharge.

Sergeant Davis, of Maryland, is accused of maltreating prisoners, stamping on their hands and feet and putting detainees in a pile on the floor to be assaulted by other soldiers. He faces a maximum of eight and a half years in jail, forfeiture of pay, reduction in rank and a dishonourable discharge.

As the session began, Sergeant Davis's lawyer argued that the soldier's rights were violated in the first Article 32 hearing, which recommended criminal charges be filed, because the Army did not make one witness, a prisoner at Abu Ghraib, available during the first proceeding.

The Army has argued that a sharp rise in violence around the Abu Ghraib prison in April, including the siege of nearby Fallujah, made the area around the detention centre too dangerous. One witness said convoys to and from the prison were sent out on an emergency basis only and they required the permission of a colonel or general to meet the defence request.

The seven soldiers charged were from the 372nd Military Police Company, an Army Reserve unit from Cresaptown, Maryland. The abuse scandal broke in April when CBS's 60 Minutes aired photographs of hooded and naked prisoners. Since then other photographs showing sexual humiliation have surfaced in a scandal that has sparked massive international criticism and undercut the moral authority of the United States-led mission in Iraq.

A hearing for Lynndie England, 21, will be held separately on Tuesday at Fort Bragg, North Carolina, where she is now stationed.

The military has not decided whether to refer the cases against two other, Specialist Sabrina Harman and Megan Ambuhl, to courts martial.

Coalition officials said the judge wanted to complete all three Baghdad hearings today but that the proceedings could last for three days.

Graner, Frederick and Davis waived their rights to have charges read aloud and their pleas were deferred when they last appeared in court May 19. They have not been detained. Since being charged, however, they've "been reassigned to duties not related to any kind of detention operation," a coalition official said.

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