The 39-year-old Army major worked at the Walter Reed Army Medical Center pursuing his career in psychiatry, as an intern, a resident and, last year, a fellow in disaster and preventive psychiatry. He received his medical degree from the military’s Uniformed Services University of the Health Sciences in Bethesda, Md., in 2001.

While an intern at Walter Reed, Hasan had some “difficulties” that required counseling and extra supervision, said Dr. Thomas Grieger, who was the training director at the time.

But, more recently, federal agents grew suspicious.

At least six months ago, Hasan came to the attention of law enforcement officials because of Internet postings about suicide bombings and other threats, including posts that equated suicide bombers to soldiers who throw themselves on a grenade to save the lives of their comrades.

They had not determined for certain whether Hasan is the author of the posting, and a formal investigation had not been opened before the shooting, said law enforcement officials who spoke on condition of anonymity because they are not authorized to discuss the case.

In an interview with The Washington Post, Hasan’s aunt, Noel Hasan of Falls Church, Va., said he had been harassed about being a Muslim in the years after the Sept. 11, 2001, terror attacks and he wanted out of the Army.

A military official told The Associated Press that Hasan was in the preparation stage of deployment, which can take months. The official said Hasan had indicated he didn’t want to go to Iraq but was willing to serve in Afghanistan. The official did not have authorization to discuss the matter publicly and spoke on condition of anonymity.

There have been reports that he was harassed for his Muslim religion, but the official says there is no indication Hasan filed a complaint.

Retired Army Col. Terry Lee, who said he worked with Hasan, told Fox News that Hasan had hoped President Barack Obama would pull troops out of Afghanistan and Iraq. Lee said Hasan got into frequent arguments with others in the military who supported the wars, and had tried hard to prevent his pending deployment.

On a form filled out by those seeking spouses through a program at the mosque, Hasan listed his birthplace as Arlington, Va., but his nationality as Palestinian, Khan said.

Nothing stood out about Hasan as radical or extremist, Khan said.

He served eight years as an enlisted soldier. Military records show he also served in the ROTC as an undergraduate at Virginia Tech in Blacksburg and received a bachelor’s degree in biochemistry there in 1997.

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Associated Press writers Lara Jakes, Pam Hess, Lolita C. Baldor and Brett Zongker in Washington; Alicia Chang in Los Angeles; and Sue Lindsey in Roanoke, Va., contributed to this report.