FORT HOOD, Texas (CNN) -- With a military judge refusing to allow a majority of the evidence prosecutors contend goes to the motive in a shooting rampage at Fort Hood, the Army psychiatrist who admitted to the killings may begin his defense as early as Tuesday.
Maj. Nidal Hasan is defending himself against 13 counts of murder and 32 counts of attempted murder in the November 5, 2009, attack, raising the question of whether he will take the stand.
And if he does, what will he say?
Hasan, 42, admitted to opening fire at a processing center for soldiers deploying to Afghanistan and Iraq, telling a military jury of 13 officers during his opening statement: "The evidence will clearly show that I am the shooter."
The judge, Col. Tara Osborn, has barred Hasan from arguing "defense of others," claiming he carried out the shooting to protect Taliban leaders in Afghanistan from the U.S. military.
"We mujahedeen are trying to establish the perfect religion," he told the jury last week. But, he added, "I apologize for the mistakes I made in this endeavor."
Hasan has previously indicated that he intends to call himself and two witnesses to the stand. If he testifies, Hasan is expected to discuss religious justification for his actions.
While the military has avoided labeling Hasan a terrorist or charging him as such, prosecutors wanted to use evidence to show that the devout Muslim had undergone a "progressive radicalization," going so far as to give academic presentations in defense of suicide bombings.
Hasan, who was scheduled to deploy to Afghanistan, did not want to fight against other Muslims and believed "that he had a jihad duty to kill as many soldiers as possible," lead prosecutor Col. Michael Mulligan has said.
The judge, Col. Tara Osborn, excluded much of the evidence that the prosecution contends goes to the heart of the motive, including e-mail communications between Hasan and Anwar al-Awlaki, the U.S.-born cleric who officials say became a key member of al Qaeda in the Arabian Peninsula. He was killed in U.S. drone strike in 2011.
Osborn ruled that the e-mails would have to be "redacted to prevent undue prejudice by association" and would diminish its use as evidence.
She also declined to allow prosecutors to use materials they maintain show Maj. Nidal Hasan's interest in the actions of Army Sgt. Hasan Akbar, the Muslim American soldier sentenced to death for killing two soldiers and wounding more than a dozen others at the start of the Iraq war,
Along with the e-mails and the material related to Akbar, Osborn also declined to allow the use of Hasan's academic presentation on suicide bombings, saying "motive is not an element of the crime."
The judge did allow prosecutors to use evidence of Hasan's Internet searches on jihad and the Taliban in the days and hours before the attack.
Just two hours before the shooting, a search of Hasan's Acer netbook computer showed that someone had pulled up and read an article entitled "Pakistan Taliban Chief Urges Taliban to Fight Army," FBI Special Agent Charles Cox III, a computer forensics examiner, testified.
Defense or lack of it
Much has been made about Hasan's defense or, as his stand-by attorneys have said, the lack of it, indicating he is perhaps more eager to prove he is a martyr than to avoid a death sentence.
Hasan refused to enter a plea at the outset of the court-martial after the judge barred him from pleading guilty. Under military law, defendants cannot enter guilty pleas in capital punishment cases.
The judge on Monday raised again concerns about Hasan acting as his own attorney after he admitted last week he did not understand that by listing someone as a witness he gave up the right of privileged communication with that person.
"Remember when I told you that I thought you would be better off with a trained lawyer?" Osborn asked.
Hasan responded: "Repeatedly."
"I've advised you before and I'm advising you again that it's not a good policy to represent yourself. ... Do you understand that?" Osborn said.
Hasan said: "Yes, I do."
Throughout most of the court-martial, Hasan has declined to cross-examine prosecution witnesses.
But on Monday, in a rare courtroom exchange, Hasan challenged a witness's account of the police shootout that ended the rampage. He was shot and left paralyzed from the chest down.
The exchange occurred after prosecution witness Sgt. Juan Alvarado testified to seeing Hasan shoot a police officer and then shoot her again while she was down.Fort Hood victims denied benefits
"I don't want to put words in your mouth. Are you saying that she was disarmed and that I continued to fire at her?" Hasan asked.
Alvarado responded: "Yes."
"I have no more questions," Hasan said.
Hasan appeared to be trying to cast doubt on Alvarado's testimony that he shot a wounded, unarmed female police officer. The officer earlier testified that after Hasan shot her, he kicked her weapon out of her reach.
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