Sitting in a wheelchair, his voice soft but unwavering, Army psychiatrist Nidal Malik Hasan took responsibility Tuesday for the 2009 mass shooting at Fort Hood.

“Fellow members, good morning,” Hasan began at the opening of his court-martial at the Army post here in central Texas. “On November 5, 2009, 13 U.S. soldiers were killed and many more injured. The evidence will clearly show that I am the shooter.”

Hasan, a 42-year-old American-born Muslim who is representing himself, was in a small courtroom just miles from Fort Hood’s Soldier Readiness Processing Center, where he said he opened fire four years ago on fellow soldiers preparing to deploy to Afghanistan.

Dressed in Army fatigues and with a full-length beard in defiance of military regulations, Hasan spoke for little more than a minute as he addressed the panel of 13 military officers who will decide whether he should be executed. He said he had been on the wrong side of a war against Islam and had switched over.

“We the mujahideen are imperfect Muslims trying to establish the perfect religion in the land of the supreme God,” said Hasan, a major, who is paralyzed from the waist down after being shot by Army civilian police officers. He apologized for “any mistakes I’ve made in this endeavor.”

Nidal Hasan, the army major accused of carrying out the worst non-combat attack on a U.S. military base in history, will defend himself against charges. (Reuters)

During a busy day of testimony, Hasan made little effort to mount a defense. He asked few questions when he had the opportunity to cross-examine 12 witnesses, who included victims of the shooting, preferring to sit placidly and occasionally shuffle his legal papers.

Staff Sgt. Alonzo M. Lunsford Jr., who lost sight in his left eye as a result of injuries suffered during the shooting, fixed Hasan in his gaze as he testified that the shooter had followed him outside and fired into his back as he tried to crawl away. Hasan declined to cross-examine him.

Earlier in the day, the defendant lowered his head and stared at a table as Col. Steve Henricks, a military prosecutor, gave a detailed account of Hasan’s radicalization, his preparation for the mass shooting and the day itself.

The Army lawyer said the psychiatrist — who worked at what is now Walter Reed National Military Medical Center between 2003 and 2009 — meticulously prepared for months and deliberately targeted those in uniform while sparing civilians. Henricks said the accused, who was also scheduled to go to Afghanistan at the end of November 2009, “did not want to deploy, and he came to believe he possessed a jihad duty to kill as many soldiers as possible.”

The court heard that Hasan had researched suicide bombers and paid for a membership at a nearby shooting range, training himself to consistently hit the head and chest of targets from 100 yards away. In the hours before the shooting, Hasan gave away some of his belongings, led the call to prayer at a local mosque, and used his computer to read an article that described Taliban leaders urging their followers “to commit jihad and not be cowards,” Henricks said.

Employees of a Killeen gun store later testified that Hasan purchased an unusually large amount of ammunition and evaded questions about what he intended to do with it.

Speaking for just under an hour, Henricks described how Hasan had entered the processing center shortly after 1 p.m. with two guns, one of them equipped with two laser sights, concealed in the pockets of his Army uniform.

Inside, dozens of soldiers were waiting for blood testing.

Hasan told the only civilian in the waiting area, a data entry clerk, to leave the room. He then stood behind a desk, shouted “Allahu akbar!” meaning “God is great,” and “opened fire on unarmed, unsuspecting and defenseless soldiers,” Henricks said.

As Hasan methodically stalked through the building, Michael Cahill, a physician’s assistant, emerged and tried to tackle him with a chair, the prosecutor said. Cahill was the only civilian killed during the attack. Another victim, who was pregnant, allegedly pleaded with Hasan for the life of her unborn child, and one witness heard shouts of “My baby! My baby!” Henricks added.

After walking outside, Hasan was twice confronted by soldiers attending a graduation ceremony in a nearby building. He told one “that a training exercise is going on and that he’s carrying a paintball gun,” and he assured another that there was nothing to worry about, Henricks said. Both men were in civilian clothes to attend the graduation and were unharmed.

The psychiatrist was shot in the chest by an Army police officer minutes later, ending the shooting spree. Investigators later found 146 spent rounds inside the building and a further 68 casings from Hasan’s gun outside.

The hearing took place amid high security. Almost 100 U.S. and foreign journalists covered the opening day of the trial, which was also attended by several family members of the victims.

Col. Tara Osborn, the military judge in the case, warned the attendees: “Some of the evidence you are going to hear may be graphic and it may be emotional . . . but the court has a responsibility to ensure that this trial is conducted with proper decorum.”