Prosecution witness Private First Class Bradley Mason said one of those charged, Staff Sergeant Raymond Girouard, told him if he were arrested he would try to get out of it on medical grounds because he had Post Traumatic Stress Disorder.

"They just smiled," said Mason. "I told him (Girouard) that I am not down with it. It's murder."

The soldiers -- Private First Class Corey Clagett, Specialist William Hunsaker, Girouard and Specialist Juston Graber -- are from the 101st Airborne Division and were serving in Samarra, north of Baghdad.

They have said the men who were killed were trying to escape during the shootings on or around May 9.

Mason, under cross-examination, said the rules of engagement were "we get to kill all the male insurgents".

The defendants have been charged with premeditated murder, attempted murder, conspiracy, communicating a threat, and obstructing justice in the killings north of Baghdad.

A premeditated murder conviction can bring the death penalty under U.S. military law.

The deaths took place during a raid on a suspected insurgent training camp near Thar Thar Lake, southwest of Tikrit. At the time, the military said more than 200 people were detained.

A Colonel Michael Steele had given orders to "kill all of them" during the operation, said Mason.

But this was directly contradicted by another prosecution witness, Captain Jason Sienko, executive officer of Charlie Company, in which all four accused men served.

"Col. Steele specifically said during our combined arms rehearsal that we're not just to go to the island and shoot everyone. 'Make sure you have well-aimed shots. Make sure we're killing the people that need to be killed'," he said Steele said.

The Article 32 hearing to determine if they will face courts-martial is being held at Contingency Operating Base Speicher in Saddam Hussein's home town of Tikrit, 175 km (110 miles) north of the capital.

It comes at a sensitive time when the military is investigating other cases of alleged abuses -- including the killings of up to 24 unarmed civilians in the town of Haditha last year by U.S. Marines -- which have infuriated Iraqis.

Mason said Girouard told him: "If you say anything, I'll kill you."

"I took them pretty seriously," said Mason.

The military had issued a statement hailing the success of Operation Iron Triangle, a three-day raid launched on May 9 on the Muthana Chemical Complex, a sprawling plant closed after the fall of Saddam in 2003.

Mason described the raid as a competition for kills.

"I know he (Steele) said 'good job' after we killed one of them, that's another terrorist down," he said.

The trial is scheduled to resume on Thursday.