A U.S. soldier was sentenced to 100 years in prison Thursday for his role in the gang rape and slaying of an Iraqi girl and the killing of her family.

Sgt. Paul E. Cortez, 24, was one of five American soldiers implicated in the notorious attack in March 2006 in Mahmoudiya, a town 30 kilometres south of Baghdad.

Cortez is the second soldier from the 101st Airborne Division to be sentenced, while the three others are awaiting trials.

Before Cortez's sentence was handed down Thursday by a military court in Fort Campbell, Ky., he apologized for raping 14-year-old Abeer Qassim al-Janabi and killing her, her parents and her younger sister.

Cortez, tears rolling down his face, said he could not explain why he took part.

"I still don't have an answer," Cortez told the military judge hearing the case, Col. Stephen R. Henley.

"I don't know why. I wish I hadn't. The lives of four innocent people were taken. I want to apologize for all of the pain and suffering I have caused the al-Janabi family."

Cortez, who is from Barstow, Calif., pleaded guilty earlier in the week to four counts of felony murder, rape and conspiracy to rape.

He was found not guilty of more serious charges of premeditated murder and conspiracy to premeditated murder.

The court gave Cortez a dishonourable discharge from the military.

He will be eligible for parole in 10 years, according to the terms of his plea agreement.

Actions out of character: fellow soldiers

Psychologist Charles Figley had testified that Cortez and the other soldiers likely suffered stress brought on by fatigue and trauma.

"It eats you up," Figley said. "It's a horrible thing. This is not unique. We've seen this in other wars."

Soldiers who served with Cortez in Iraq testified that his actions were out of character. They described the hardships of serving in Iraq, including sleep deprivation and the lack of running water. 

"I just never would have seen it coming," said Staff Sgt. Tim Briggs, who has known Cortez for five years.

Prosecutors argued that stress was no excuse.

On Wednesday, Cortez described the graphic details of the attack to the court, explaining how he and Specialist James Barker raped the girl in her family home.

Cortez said former private Steven D. Green raped the girl in front of him. Green then shot her father, mother and sister before turning his gun on the girl and shooting her in the head.

Cortez said the soldiers attempted to burn the girl's body to hide the evidence. They also burned their own clothes and threw the gun, an AK-47, in a canal.

Barker, 24, pleaded guilty to rape and murder in November 2006 and was sentenced to 90 years in military prison.

Pte. 1st Class Jesse Spielman, 22, and Pte. 1st Class Bryan Howard, 19, await courts martial.

Green is accused of being the ringleader of the group. He was discharged from the military before being charged and will be prosecuted in a federal court in Kentucky.

With files from the Associated Press