US Army major Nidal Hasan is to come face to face with dozens of people he is accused of attacking during a massacre that killed 13 at a Texas base.
An Article 32 hearing, which starts in military court and is expected to last at least three weeks, will determine whether there is enough evidence to put the army psychiatrist on trial. It will also be the first time witnesses have testified about the worst shooting on a US military base.
Such hearings are unique to military court, where prosecutors and the defence can call witnesses and both sides are able to question them and present other evidence.
Hasan, 40, is charged with 13 counts of premeditated murder and 32 counts of attempted premeditated murder. When the proceedings begin, he will be sitting just a few feet from the witnesses, who are expected to give graphic details of the attack.
The shootings happened last autumn at Fort Hood, one of America's largest army posts. About 300 people were in the Soldier Readiness Processing Centre, where soldiers must go before they are deployed to update vaccinations, get eye tests and dental screenings, finalise their wills or sign up to talk to a chaplain.
As soldiers waited in various lines, a man suddenly jumped up on a desk, shouted "Allahu Akbar!" - Arabic for "God is great!" - and started firing two guns, witnesses said.
The soldiers and civilian workers were unarmed as 100 rounds came at them directly or ricocheted off the desks and tile floor.
The rampage lasted only about 10 minutes until two Fort Hood police officers shot and wounded Hasan, who is now paralysed.
The dead were aged from 19 to 62 and included a pregnant soldier who had just returned from Iraq and a young father excited about his first deployment.
Three who died and six who were seriously injured were in the same army reserve unit that Hasan was supposed to deploy with the following month. The Madison, Wisconsin-based 467th Medical Detachment had just arrived at Fort Hood, so it was unclear if Hasan knew any of the 40 members or was targeting them. Most of the unit, which provides counselling and other mental health services for soldiers, deployed to Afghanistan as scheduled a month after the attack.