He was the second to plead guilty and be sentenced in the case, one of the most high profile of several atrocities allegedly committed by US troops in Iraq.
Last November, Specialist James Barker was sentenced to 90 years in prison as part of a plea deal in the case.
Court debate
On Wednesday, prosecutors and the defence in the military court argued the last outstanding charge against Cortez; whether the four murders were premeditated.
After lengthy debate, the judge moved to drop that action, allowing the court to move forward to sentencing on five charges of premeditated conspiracy to commit rape, four counts of felony murder, rape, violation of a general order (consuming alcohol) and breaking into a house.
Two other soldiers in the case are awaiting military courts martial, while a fifth, who was discharged from the army before the case came to light, will be tried in federal court at a later date.