A US Army psychiatrist has admitted to opening fire on fellow soldiers at the Fort Hood military base in Texas, as he took charge of his own defence at a high profile trial.
"The evidence will clearly show I am the shooter," declared Major Nidal Malik Hasan, who has fired his lawyers and is representing himself, in his opening statement in Tuesday.
Hasan, who has previously admitted to killing 13 people and wounding 32 others in the 2009 attack at Fort Hood, faces the death penalty if convicted.
Military law prohibits him from pleading guilty to a capital offence and so Hasan has been given the opportunity to try to convince a jury of 13 officers that he does not deserve death for his actions.
The attack jolted the US military and prompted calls for stronger safeguards against internal security threats and "homegrown" terror attacks.
Nearly four years after being attacked in what should have been the safety of a protected base, survivors are steeling themselves to be cross-examined by Hasan, the man who shot them.
Military judge Colonel Tara Osborn will try to ensure Hasan does not use the high-profile trial as a platform to espouse extreme views and that he treats witnesses with respect.
Shawn Manning, a mental health specialist in the same unit as Hasan who was shot six times, said he was dreading the prospect of being cross-examined by his former colleague.
Manning is the lead plaintiff in a lawsuit urging the military to reclassify the shooting as "terrorism" instead of the current designation of "workplace violence," which offers less compensation to victims.
Osborn has barred prosecutors from mentioning terrorism as a motive and prohibited Hasan from using a "defence of others" strategy to justify his actions.
Hasan, 42, was due to deploy to Afghanistan weeks after the attack. He has said that he shot soldiers to protect his fellow Muslims from an "illegal" war.
Born in the eastern US state of Virginia to Palestinian parents, Hasan joined the Army in 1995.
It was during a residency at Walter Reed Army Medical Center from 2003 to 2006 that Hasan first exhibited signs of radical Islamic views, according to an FBI report entitled "A Ticking Time Bomb."
Hasan attended a mosque where radical US-born cleric Anwar al-Awlaki - a key figure in Al-Qaeda in the Arabian Peninsula until his death in a 2011 drone strike in Yemen - worked in 2001.
Hasan has managed to delay the trial with various legal manoeuvres and a lengthy battle over whether he could violate military rules by wearing a beard.
Osborn has estimated the trial could last anywhere between one and four months.
More than 250 witnesses are set to testify against Hasan, including family members of each of the 13 killed in the shooting and the 32 soldiers and civilians who were wounded.
Hasan has said he only intends to call two witnesses in his defence.