The hearing is being held at Fort Leavenworth, Kansas. Army Sgt. John Russell is facing several charges in the 2009 shooting spree, including premeditated murder.
Russell is accused of carrying out the deadliest act of soldier-on-soldier violence during the war in Iraq. The case brought attention to the issues of combat stress and morale as troops increasingly served multiple combat tours.
Russell had gone to counseling to deal with combat stress, but an investigation found lapses in how the military monitored him and how authorities responded once the shooting began at a base on the edge of Baghdad.
Russell, who was assigned to the 54th Engineer Battalion of Bamberg, Germany, was near the end of his third deployment when the shooting occurred in May 2009.
According to the report, Russell was on his fourth visit to the clinic when the appointment was cut short because he became uncooperative. Military police were called in and ordered him returned to his unit.
Less than an hour later, he grabbed an M-16 rifle from a fellow soldier, stole a white Ford Explorer SUV and returned to the counseling facility, according to the report. As the shooting began, a soldier in another room of the counseling facility reported hearing repeated gunshots and scrambled out of a window to safety.
On Monday, a military officer will hear evidence and decide if Russell should face a military trial. Legal analysts say it's similar to a civilian grand jury.
The Associated Press contributed to this story.
