Pfc. Corey R. Clagett, 22, was one of four soldiers from the division's 3rd Brigade "Rakkasans" who were accused in the detainees' deaths during a May 9 raid on the Muthana chemical complex in Samarra, about 60 miles north of Baghdad.
In an agreement with prosecutors, Clagett pleaded guilty to charges of murder, attempted murder, conspiracy to commit murder and conspiracy to obstruct justice. Prosecutors dropped a second obstruction charge and charges of disrespecting an officer and threatening.
Clagett will also be demoted to private and dishonorably discharged. If he does not cooperate with prosecutors, he could be sentenced to life in prison with a chance at parole.
The soldiers first told investigators they shot the detainees because they were attempting to flee — a story they now say they made up — and that commanders had given them orders to kill all military-age males on the mission.
Two of those soldiers, Spc. William B. Hunsaker and Spc. Juston R. Graber, have changed their stories and pleaded guilty. The squad leader, Staff Sgt. Raymond Girouard, is awaiting his court-martial.
"(Sgt. Girouard) said we were going to cut the zip ties loose and kill the detainees," Clagett told the military judge, Col. Theodore Dixon, on Thursday. "I knew it was an unlawful order. I just went along with it."
The judge asked Clagett what his intention was when he shot at the detainees.
"To kill them, your honor," Clagett said.
Prosecutors said Clagett fatally shot one detainee and seriously wounded another. Official say Graber then killed the wounded detainee, and Hunsaker killed the third.
Clagett's lawyer, Paul Bergrin, has insisted Clagett was following orders, but sought the plea agreement after Hunsaker, 24, told a military judge that Clagett helped him shoot the detainees.
"My client was 100 percent convinced at all times that the individuals that were killed were terrorists," Bergrin told reporters after the sentencing. "His heart is bleeding that he can no longer serve his country."
Military prosecutors would not discuss the case.
Hunsaker pleaded guilty to murder, attempted murder and obstruction of justice this month and was also sentenced to 18 years in prison.
Graber, 21, pleaded guilty to a lesser charge of aggravated assault with a dangerous weapon as part of his agreement to cooperate with prosecutors. He was sentenced to nine months in military jail.
Hunsaker testified that Girouard cut him on the face and arm to make it appear there was a struggle after he and Clagett killed the detainees. Clagett repeated that story to the judge Thursday.
"Just like anyone, we didn't want to get caught," Clagett said.
The case is one of two involving soldiers from the 101st Airborne Division accused of killing Iraqis during a deployment to the Middle Eastern country that ended in September.
Four other soldiers from the division's 2nd Brigade Combat Team are accused of raping and killing an Iraqi teenager and killing three others in her family last March. A former Army private also faces murder and rape charges in federal court for the same incident.