A former soldier who could be sentenced to death for rape and murder in Iraq had a difficult childhood after his parents divorced and at times shuttled among friends and relatives, the man's stepfather testified Wednesday.

Relatives and former high school classmates described former Pfc. Steven Dale Green as someone trying to put together a family from relatives and friends after his parents divorced when he was 4.

Their testimony case on the third day of the penalty phase of Green's trial. He was convicted last week of raping and murdering 14-year-old Abeer Qassim al-Janabi and fatally shooting her family in a March 2006 attack at their home in Mahmoudiya, Iraq, about 20 miles south of Baghdad.

Earlier Wednesday, two former Marine officers testified in federal court that Green had an unusually stressful combat tour in a unit that suffered heavy casualties and didn't receive sufficient Army leadership.

Green first lived with his mother, who remarried in 1993, jurors heard. The man's stepfather, Daniel Carr, said the family moved frequently and Green's mother wasn't affectionate with her son.

"He felt he was left out of that department," Carr testified, adding the defendant lived variously with relatives or friends at times during high school.

By 2004, Green was determined to get into the military. Green obtained a high school diploma and joined the Army before heading to basic training in 2005, Carr added.

"He wanted that more than anything," Carr said.

Within six months, Pfc. Green deployed to Iraq with the Fort Campbell, Ky.-based 101st Airborne Division.

High school classmate Chase Bentley played football and ran track with Green. While Green wasn't the best athlete, Bentley told jurors he was a good teammate and one who was "fun to watch." His comment drew a smile from Green.

Another former classmate, Cody Ray, testified about a funny kid who amused friends by crushing cans on his head or playfully breaking into a "chicken dance."

"He perfected that dance," Ray said of his former classmate.

Green, 24, of Midland, Texas, is being tried in civilian court because charges were filed after he was discharged from the Army.

Retired Marine Lt. Col. Andrew Horne and former Marine lawyer Gary Solis testified Wednesday that stress from combat can impair a soldier's judgment and good leadership is needed to prevent criminal acts.

Horne, of Louisville, reviewed the Army's investigation into the attack, and offered expert assessment of the conditions Green served in. He told jurors that Green's small unit lost a high number of soldiers in a short time.

Enemy attacks killed two command sergeants, a lieutenant and a specialist in Green's unit during 12 days in December 2005.

"This unit suffered some of the most extraordinary casualties in a short period of time and were exposed to the worst threats and risk I've seen in my experience," said Horne, who served in Iraq in 2005.

Solis, who teaches law at Georgetown University in Washington, D.C., said facing such stressful conditions can impair a soldier's judgment, especially when the unit lacks leadership.

"It's not long before judgment is degraded," said Solis, a veteran of two tours in Vietnam. "That's what leaders are for. To help soldiers."

Prosecutors on Monday told jurors that Green's crime was so heinous it warranted a death sentence. Defense attorneys said Green didn't act alone, and yet none of the other soldiers who participated in the attack faced a death sentence.

Three other soldiers are serving time in military prison for their roles in the attack, and testified against Green at his trial.