A former U.S. Army soldier accused of raping and killing a 14-year-old Iraqi girl and slaying her family was upset after losing several friends in combat but didn't appear to struggle more than anyone else in his unit, one of his commanding officers testified.

Steven Dale Green, 23, of Midland, Texas, has pleaded not guilty to more than a dozen charges, including sexual assault and four counts of murder, stemming from the March 2006 attack in Iraq's so-called "Triangle of Death." He is being tried in federal court in connection with the girl's rape and killing and the deaths of her mother, father and a 6-year-old sister.

Col. Todd Ebel told jurors on Monday, the opening day of trial, that he spoke with Green in December 2005 about losing soldiers to enemy attacks. But, Ebel said, beyond frustration, the private first class with the 101st Airborne Division didn't appear unfit to remain in the Army.

"Yes, he was frustrated with Iraqis," Ebel said. "Mostly, he was frustrated with the idea that we can't recognize them. They don't wear uniforms."

Ebel, who oversaw Green's unit, resumed his testimony Tuesday, telling jurors that the soldiers were in a violent area of Iraq. He said his brigade, which included Green, lost 46 soldiers in combat-related deaths during its yearlong deployment.

Prosecutors said in opening statements that Green and three other soldiers attacked the family at their home near Mahmoudiyah, Iraq, about 20 miles south of Baghdad. Assistant U.S. Attorney Brian Skaret said Green fatally shot the rest of the family before becoming the third soldier to rape the teenager.

After he shot the girl in the face several times, Green used kerosene to set fire to her body, Skaret said.

"They left behind the carnage of all carnage," Skaret said.

Skaret told jurors that a group of soldiers, including Green, was playing cards and drinking whiskey at a checkpoint. Talk turned to having sex with Iraqi women, when one soldier mentioned the al-Janabi family, who lived nearby, Skaret said.

Skaret said Green used a shotgun to kill the three family members in a room and told the soldiers that the family was dead.

He then raped the girl and shot her, according to Skaret. Later, Green would talk about the killings to superior officers, other soldiers and even civilian friends, Skaret said.

In Green's defense, attorney Patrick Bouldin painted a picture of young soldiers in harsh wartime conditions, lacking leadership and receiving little help from the Army to deal with the loss of their friends.

Bouldin said before the attack, Green had lost five colleagues in combat, including four in a short span.

He said soldiers had lost so many friends and leaders they could no longer perform their duties.

"Context," Bouldin said. "You've got to understand the context."

Green is being tried in a civilian court because he was discharged from the Army before being charged. His trial is being held in Paducah because of the western Kentucky city's proximity to Fort Campbell on the Kentucky-Tennessee border, where Green was based with the 101st Airborne.

Other soldiers involved in the attack were prosecuted in military court, including two who pleaded guilty and acknowledged taking part in the rape. Prosecutors said a third who was convicted had gone to the family's home knowing what was planned. A fourth who stayed behind at the checkpoint pleaded guilty to being an accessory, they said.

Green's discharge papers show he received an honorable discharge in May 2006 after being diagnosed with a personality disorder.

Bouldin said Green was prescribed a mood-stabilizing drug, but the Army never followed up on his mental state before the attack.

"He told the psychologist, 'I'm so upset. I'm having trouble here. I want to kill all these guys (Iraqis) because I can't tell them apart,"' Bouldin said.