FORT HOOD, Texas — A military judge blocked several key pieces of evidence Monday that prosecutors said would explain the mindset of the soldier accused in the 2009 shooting rampage at Fort Hood, including his belief that he had a “jihad duty” to carry out the attack.
Prosecutors had asked the judge to approve several witnesses and various evidence to support what they allege motivated Major Nidal Hasan to kill 13 people and wound more than 30 others at the Texas military base. But the judge, Colonel Tara Osborn, blocked nearly all of them.
Osborn barred any reference to Hasan Akbar, a Muslim soldier sentenced to death for attacking fellow soldiers in Kuwait during the 2003 Iraq invasion.
Prosecutors wanted to prove that Hasan, an American-born Muslim, wanted to carry out a ‘‘copycat’’ attack, but the judge said introducing such material would ‘‘only open the door to a minitrial’’ of Akbar.
She also said such evidence would result in a ‘‘confusion of issues, unfair prejudice, waste of time, and undue delay.’’
The judge said prosecutors also couldn’t introduce three e-mails, ruling that the needed redactions would make them irrelevant.
The contents of the e-mails were never disclosed, but the FBI has said Hasan sent numerous e-mails starting in December 2008 to Anwar al-Awlaki, a radical US-born Islamic cleric killed by a drone strike in Yemen in 2011.
The judge also told prosecutors that they couldn’t cite Hasan’s interest years ago in conscientious objector status and his past academic presentations. Osborn said such evidence was too old and irrelevant.
However, the judge will allow evidence about Internet searches on Hasan’s computer around the time of the attack and websites that Hasan had listed as ‘‘favorites.’’ Osborn said that information was more timely.
Military prosecutors opened the trial by saying they would show that Hasan felt he had a ‘‘jihad duty,’’ referring to a Muslim term for a religious war or struggle.
After calling almost 80 witnesses during the last two weeks, prosecutors said Friday that they would begin tackling the question of motive this week.
Hasan — who is acting as his own lawyer but has mostly sat in silence — could soon shed light on such questions, if prosecutors rest their case as expected this week. If Monday was any indication, he may be ready to talk.
In one of the first times during testimony, Hasan spoke up, first to challenge the government’s definition of “jihad” and to question a witness.
Hasan briefly cross-examined Staff Sergeant Juan Alvarado, who saw a gunfight between Hasan and Kimberly Munley, one of the Fort Hood police officers who responded to the shootings.
Alvarado said Hasan tried to shoot Munley after she had been shot and disarmed.
“Are you saying — and I don’t want to put words in your mouth — are you saying that after it was clear that she was disarmed, I continued to fire at her?” Hasan asked.
Alvarado said that was correct.
The exchange marked the first time Hasan has questioned a witness to the shooting.
And earlier Monday, Hasan asked that the definition of “jihad” be adjusted.
Prosecutors didn’t object, and jurors were told: “under Islam, the central doctrine that calls on believers to combat enemies of the religious belief.”
Such moments have been rare during the trial.
Again Monday, the judge urged Hasan to forgo representing himself and to allow trained lawyers to take over.
Osborn told Hasan she believed he would be better off with a lawyer who knew the rules for military trials, such as when to raise objections and how to spot issues that could be cited on appeal.