Fort Hood, Texas (CNN) -- "I am the shooter."
Maj. Nidal Hasan made that blunt declaration Tuesday at the outset of his court-martial in the 2009 massacre at Fort Hood. The Army psychiatrist is charged with killing 13 and wounding 32 at a processing center for soldiers heading into combat zones overseas.
"The evidence will clearly show that I am the shooter," Hasan told the panel of 13 senior officers who will decide his fate. "The evidence presented with this trial will show one side. The evidence will also show that I was on the wrong side. I then switched sides."
But the declaration wasn't exactly news to now-retired Staff Sgt. Alonzo Lunsford, who was shot seven times that November day. Lunsford, the first of several survivors scheduled to testify against Hasan, recounted how the now-admitted gunman rose from a chair in the processing center, pulled out a pistol and began shooting.
"It was a state of panic," Lunsford said. A civilian doctor, Michael Cahill, tried to hit Hasan with a chair to stop the shooting; Hasan shot him dead. Soldiers tried to flee or take cover inside the processing center as Hasan fired dozens of shots.
As Lunsford was checking behind him, "Major Hasan is turning the weapon on me," he said. "He has a laser on his weapon and it goes across my line of sight and I blink. In that time, he discharges his weapon. The first round, I'm hit in the head."
A second shot caught Lunsford in the back. He decided to play dead for a while before changing his mind and deciding to run for the door. He made it out of the building but was shot five more times outside, he testified.
Hasan continued shooting at Lunsford even as he was receiving first aid outside the processing center, before police arrived. Officers shot and wounded Hasan, ending the rampage and leaving him paralyzed from the chest down.
A U.S.-born citizen of Palestinian descent, Hasan had been scheduled to deploy to Afghanistan before the killings. Prosecutors hope to show that the devout Muslim had undergone a "progressive radicalization," giving presentations in defense of suicide bombings and about soldiers conflicted between military service and their religion when such conflicts result in crime.
Hasan did not want to deploy to fight against other Muslims and believed "that he had a jihad duty to kill as many soldiers as possible," said Col. Michael Mulligan, the lead prosecutor in the case.
Investigators found 146 spent shell casings in the room where the attack began, Mulligan said. Hasan carried two laser-sighted pistols and 420 rounds of ammunition, his pockets lined with paper towels to muffle the sounds of the magazines banging together, he said.
At the outset of his assault, Hasan cried out "Allahu Akbar ... and starts shooting at the soldiers sitting defenseless in chairs," Mulligan said.
Internet searches on Hasan's computer used keywords like "terrorist killing," "innocent," "Quran," "fatwas" and "suicide bombings," Mulligan said.
Hasan is representing himself in his court-martial and could be sentenced to death if found guilty. As his own attorney, he'll be cross-examining witnesses -- perhaps including some of those he has now admitted shooting. He did not cross-examine Lunsford, however.
He told the panel in his opening statement, "We mujahedeen are trying to establish the perfect religion." But, he added, "I apologize for the mistakes I made in this endeavor."
Hasan told his family he had been taunted after the al Qaeda attacks of September 11, 2001. Investigations that followed the killings found he had been communicating via e-mail with Anwar al-Awlaki, the Yemeni-American radical cleric killed by a U.S. drone attack in 2011.
The case was first set to begin in March 2012, but it has been delayed repeatedly -- notably over a previous judge's unsuccessful demand that the beard Hasan has grown while in custody be forcibly shaved.
Among others scheduled to testify include Chief Warrant Officer Christopher Royal, who survived the shootings with two bullet wounds to his back. The slugs left him with nerve damage that numbs his left arm and leg and sends streaking pains "shooting up and down my back."
It's also left invisible scars as well -- post-traumatic stress that has hurt his ability to perform his duties as a computer specialist and left him unable to feel safe in his own country.
"I really feel more comfortable downrange. I really do," said Royal, who served in Iraq four times and in Afghanistan once. "I think I would be more comfortable living in Iraq right now than living in the United States."
Royal escaped the gunfire only to go back into the processing center in an attempt to tackle Hasan.
"I had escaped without being wounded," Royal said. "I got ... in the parking lot, and then I said, 'I can't let him get away with this.' And I wasn't even thinking that I didn't have a weapon. I just knew that I couldn't let him get away."
Lunsford said Tuesday he encountered Royal outside the building.
"I ask him, 'Am I out of the building yet?' He says I am, and to play dead," Lunsford testified.
Josh Rubin reported from Fort Hood. CNN's Jason Morris contributed to this report.