FORT HOOD, Texas — The Army psychiatrist charged in the deadly 2009 Fort Hood shooting rampage says he'll use a "defense of others" argument when he represents himself at his upcoming murder trial.

Maj. Nidal Hasan didn't elaborate when announcing his strategy Monday, shortly after a military judge agreed to allow him to represent himself.

But it was the first time Hasan hinted at his reasoning behind the attack that killed 13 people and wounded more than two dozen others on the Texas Army post.

Hasan also asked for a three-month delay to prepare. The judge said she'd decide Tuesday, a day before jury selection was scheduled to begin.

Hasan faces the death penalty or life without parole if convicted.

To prove to a "defense of others" argument, a defendant must show a threat was imminent.

Maj. Nidal Hasan's attorneys will remain on the case but only if he asks for their help, the judge said. Hasan, 42, faces the death penalty or life in prison without parole if convicted of 13 counts of premeditated murder and 32 counts of attempted premeditated murder.

After questioning Hasan for about an hour, the judge, Col. Tara Osborn, ruled that Hasan was mentally competent to represent himself and understands "the disadvantage of self-representation." She repeatedly urged him to reconsider his request, noting that the lead prosecutor has more than 20 years of experience and that Hasan will be held to the same standards as all attorneys regarding courtroom rules and military law.

"You've made that quite clear," Hasan said after the judge asked if he understood that representing himself was not "a good idea."

At Osborn's request, a doctor testified Monday about Hasan's physical condition. The doctor said Hasan's paralysis won't have a significant impact during proceedings but that Hasan can only sit for four consecutive hours and has limitations writing. He was paralyzed from the waist down after being shot by police the day of the attack on the Texas Army post.

Hasan asked the judge to kick one of his attorneys off the case completely, but she instead said that two of his lawyers would sit at his defense table while the third sits in the courtroom. All will assist him if he asks.

Jury selection is set to start Wednesday.

Hasan in 2011 cut ties with his previous lead attorney, John Galligan, a civilian who is a former military judge. Galligan said recently that he didn't know why his former client wanted to represent himself.

At a hearing in May, Hasan told Osborn that he wanted to plead guilty. But Army rules prohibit a judge from accepting a guilty plea to charges that could result in a death sentence. Osborn also denied his request to plead guilty to lesser murder charges, citing legal issues that could have arisen because his death penalty trial still would have proceeded.

Witnesses have said that after lunch on Nov. 5, 2009, a gunman wearing an Army combat uniform shouted "Allahu Akbar!" — "God is great!" in Arabic — and opened fire in a crowded medical building where deploying soldiers get vaccines and other tests.

Witnesses said the gunman fired rapidly, pausing only to reload, even shooting at some soldiers as they hid under desks and fled the building.

Government reports on investigations after the shooting revealed that Hasan had become a "ticking time bomb" and radical extremist while he was a psychiatrist in training at Walter Reed, where he started in 2004.

The government has also said that Hasan, an American-born Muslim, had sent more than a dozen emails starting in December 2008 to Anwar al-Awlaki, a radical U.S.-born Islamic cleric killed in Yemen in 2011. According to the emails released by the FBI, Hasan asked questions indicating he was already thinking about or planning the attack.