(Updates with testimony from injured soldier, more details)
By Karen Brooks and Lisa Maria Garza
FORT HOOD, Texas, Aug 6 (Reuters) - Army psychiatrist Nidal Hasan admitted carrying out the massacre of 13 soldiers at a Texas base on the first day of his court-martial Tuesday, quietly telling a jury, "I am the shooter."
Hasan, who is representing himself in the military trial at the base where he opened fire on Nov. 5, 2009, spent less than two minutes on a statement in which he spoke of his conversion to "jihad," or Muslim holy war, against the United States.
"I was on the wrong side but I switched sides," Hasan, in a wheelchair, said without emotion. The American-born Muslim was paralyzed from the waist down after being shot by military police during the rampage at Fort Hood, which wounded more than 32 others.
The trial, delayed repeatedly, comes four years after the worst non-combat attack at a U.S. military base in history. If convicted, Hasan could be sent to death row in Fort Leavenworth, Kansas, and become the first American soldier executed by the U.S. military since 1961.
One of his victims, Sergeant Alonzo Lunsford, described the harrowing minutes of the shooting to the jury of 13 Army officers. He said Hasan pulled a gun from inside his uniform in a building where soldiers get medical examinations, shouted "Allahu Akbar" ("God is Great" in Arabic) and started shooting.
Soldiers dived for cover but Lunsford said there was nowhere to hide because Hasan had blocked the front door.
"Major Hasan is pointing his weapon at me. He has the laser across me and I blink because it's in my eyes. He discharges his weapon. The first round, I'm hit in the head. I get knocked back, spin and hit the floor," Lunsford said, rocking back and forth in his chair nervously as he testified.
"I tried to low crawl to the desk and then I'm hit in the back. At this point, I decide to play dead," he said. Hasan moved on to other victims.
Hasan did not question Lunsford.
Hasan fired on the unarmed soldiers just days before he was supposed to be deployed to Afghanistan, saying he did so to stop what he has called a U.S. war on Islam.
Lunsford said Hasan walked out of the building and continued to shoot at soldiers outside, reloading his weapon.
He was shot seven times - twice inside, once while he was exiting the building and four times while he was outside. One shot went into his skull and exited his ear, two more entered his abdomen, one in the back and two in his "left flank."
'THAT IS MY WEAPON'
Prosecutors walked jurors through the timeline of the shooting in their opening statement.
"Evidence will show that Hasan didn't want to deploy and he possessed a jihad duty to kill as many soldiers as possible," military prosecutor Colonel Steve Henricks said.
The military judge for the court-martial, Colonel Tara Osborn, has rejected Hasan's offer to plead guilty in return for being spared the death penalty.
Earlier in the day, when the weapon was presented as evidence, Hasan confirmed it was his. "Your honor, that is my weapon," he said.
A review by a former FBI director found Hasan had exchanged emails with Anwar al-Awlaki, a U.S.-born cleric linked to al Qaeda's Yemen-based wing. Awlaki was killed in a U.S. drone strike.
Hasan plans to call only two witnesses at trial, according to Fort Hood officials. The witnesses were not identified. Hasan may cross-examine any witness, including survivors.
He questioned a man who accompanied him to prayers at a mosque on the morning of the shooting. Pat Sonti said Hasan took over the microphone to lead the call to prayer even though it was Sonti's turn.
Hasan asked if there was a protocol for determining who leads prayer and Sonti said the imam signals the chosen person. Hasan was not chosen but did it anyway, Sonti said.
He faces 13 charges of premeditated murder and 32 charges of attempted premeditated murder. The dead included 12 active duty soldiers, who were unarmed when they died, and a retired chief warrant officer who worked as a civilian employee at the base.
The jury includes nine colonels, three lieutenant colonels and a major.
The trial was delayed repeatedly over procedural issues, such as whether Hasan would be allowed to keep a beard that violates military grooming regulations, which he has said he wears for religious reasons.
A unanimous verdict of guilty is required for execution to be an option. (Reporting by Karen Brooks and Lisa Maria Garza; Writing by Greg McCune; Editing by Claudia Parsons and Doina Chiacu)