Jan 12, 2007
At a military trial, Specialist William Hunsaker admitted allowing three detainees to run away before "taking careful aim" and shooting them.
He had agreed to help prosecutors bring cases against three others accused of involvement in the killings.
The detainees died during a US military operation near the Thar Thar Canal near Tikrit in northern Iraq on 9 May.
Hunsaker, 24, is the second soldier to plead guilty to charges over the killings.
On Tuesday Spc Justin Graber admitted a charge of aggravated assault with a dangerous weapon and was sentenced to nine months in jail.
At a hearing in Fort Campbell, Kentucky, Hunsaker pleaded guilty to charges of murder, attempted murder and obstruction of justice.
Two other soldiers - Pte Corey Clagett, 21, and Sgt Raymond Girouard, 24, are due to face trial in the coming months.
Hunsaker accused Sgt Girouard of giving an order to kill the three detainees.
"He told us to cut the zip ties, tell them to run and shoot them. I went out and did just that," he told the court.
All the soldiers belong to the 101st Airborne Division.
In a separate case, four soldiers from the 2nd Brigade of the 101st Airborne are also accused of the rape and murder of an Iraqi girl and her family in the town of Mahmudiya.