WASHINGTON—When Maj. Nidal Malik Hasan took his two handguns and headed for Fort Hood on Nov. 5, he left behind in his spartan apartment his new business cards. Now they are one more clue for investigators of the 13 killings he is charged with, hinting at the road not taken.

On the cards, ordered over the Internet after Hasan was transferred to the sprawling Texas base in July, the 39-year-old psychiatrist omitted the rank he had achieved in the Army he had served for most of his adult life. Instead, he included the cryptic abbreviation “;SoA,”; apparently “;Servant of Allah”; or “;Soldier of Allah,”; perhaps marking a symbolic shift of allegiance from his military profession to his increasingly consuming faith.

But a man plotting mass murder does not ordinarily plan to open a business. Whether Hasan hoped to moonlight as a private therapist specializing in Muslim patients, or imagined that he might be permitted to exit the Army early, the cards and many other clues will be studied by Army and FBI agents trying to answer the same questions that many Americans have debated over the last 10 days.

Was Hasan a terrorist, driven by religious extremism to attack fellow soldiers he had come to see as the enemy? Was he a troubled loner, a misfit who cracked when ordered to deploy to a war zone whose gruesome casualties he had spent the last six years caring for? Or was he both?

In his weekly address, President Barack Obama vowed Saturday that the administration would discover the full story of the tragedy. “;That investigation,”; he said, “;will look at the motive of the alleged gunman, including his views and contacts.”;

Obama said investigators will also look for any missteps. “;If there was a failure to take appropriate action before the shootings, there must be accountability,”; he said.

Whatever led Hasan to act, it is clear is that he felt intense pressure. He had told family members for years about his fears of being sent to war, and his work at Walter Reed Army Medical Center had exposed him daily to the horrors combat could produce. He appears to have had few social ties; one fellow psychiatrist remembers him as “;a man out on the periphery.”;

In recent years, Hasan had focused intently on the conflict he believed some Muslim soldiers felt between their religion and their country's wars in Muslim lands—though what some co-workers saw as a productive academic interest, others detected as a personal struggle.

Law enforcement officials who have been examining Hasan's writings, including a Web posting on suicide bombing they have tentatively concluded was his, say he appears to have been grappling with a question widely discussed among Muslim militants since the Sept. 11, 2001, attacks. When, if ever, is the death of innocents morally justified?

The trail of evidence investigators are following, so far at least, suggests that both emotional problems and nascent extremism spurred Hasan, who survived the bullets of the police officers who stopped him and now is charged with 13 counts of murder.

Depression and stress alone can set off lethal attacks. In Baghdad last May, for instance, a despondent Army sergeant was accused of killing five fellow soldiers at a clinic, and no one suggested that extremism had played any role.

But Dr. Michael Stone, a forensic psychiatrist in New York and an expert on mass murderers, said the emerging picture of Hasan suggests that militant religion “;seemed to provide answers to a lot of the psychological problems already stirring around in him.”;

Some experts on terrorism believe that Hasan may be the latest example of an increasingly common type of terrorist, one who has been self-radicalized with the help of the Internet, and who wreaks havoc without support from overseas networks and without having to cross a border to reach his target.

Bruce Hoffman, a Georgetown University professor who studies terrorism, said such cases had appeared at a growing rate in the last year, most of them involving people with no direct ties to foreign terrorists. The trend of self-radicalization, which Qaida leaders and allies have encouraged with a steady stream of inflammatory messages on the Web, is gaining momentum, he said.

“;You've had all shapes and sizes, which is a challenge for law enforcement,”; Hoffman said, citing a shooting at a Little Rock military recruitment center, synagogues targeted for attack in the Bronx and foiled bombing schemes in Illinois and Texas, among others.

While investigators are combing intelligence files for any foreign contacts Hasan may have had, the only significant connection the authorities have confirmed so far are a dozen or so e-mail messages he sent to a radical cleric now in Yemen, Anwar al-Awlaki.

While officials have described the messages as involving questions about Islamic interpretation, they presumably reflected the psychiatrist's familiarity with Awlaki's voluminous sermons and texts on the Web supporting violent jihad. But a counterterrorism analyst who examined the messages decided that they were consistent with authorized research Hasan was conducting and did not alert his military superiors.

Awlaki, who was born in New Mexico and served as imam in two mosques attended by three of the Sept. 11 hijackers, is known as a compelling speaker in English and Arabic whose influence has been documented in several recent cases of homegrown terrorism, including a plot to bomb government buildings in Canada and another to shoot up Fort Dix, N.J.

By December 2008, when he sent Awlaki his e-mail inquiries, Hasan appears to have been deeply engaged with applying religious values to violence. In the Web posting investigators believe was his, Hasan suggested that a suicide bomber might have just as noble a purpose as a soldier who throws himself on a grenade to protect his comrades.

“;Your intention is the main issue,”; the writer concluded.

TROUBLE CONNECTING

Hasan had spent a decade in the world of military medicine in and around Washington. He attended medical school and had a fellowship at the Uniformed Services University of the Health Sciences, and did his psychiatric residency at Walter Reed Army Medical Center.

It was a scholarly life on leafy campuses, very different from his gritty childhood—his parents ran a notoriously rough bar in downtown Roanoke, Va.,—and from the hard routine of an enlisted soldier. He often struggled, but just as often got academic counseling or other support. His seeming inability to connect with people sometimes undermined his work. More than one patient said of him, “;He meant well, he was kind, but he didn't get me,”; one former colleague at Walter Reed recalled. When co-workers went out to socialize, Hasan went home or to the mosque in Silver Spring, Md. where he regularly attended services.

“;You could see who was buddy-buddy, and he just seemed definitely quieter and not part of that,”; said Nancy Meyer, a social worker who was a contractor at Walter Reed.

When he did engage, he often seemed argumentative. When instructors or peers tried to offer advice that conflicted with his own views, he would become “;passively rigid,”; said the colleague, who asked not to be named because the Army is still investigating the case. Hasan opted out of the personal psychotherapy offered to residents as a routine part of psychiatric training.

“;That was Nidal,”; the colleague said. “;He seemed to want to do things, but there was this hesitation there always, this avoidance.”;

He told others he liked “;the consistency”; of the Army. But he was so concerned about being sent to war that at Walter Reed, relatives said, he began researching ways to get an early discharge. He abandoned the effort when he decided he could not succeed.

Part of his disenchantment was his deep and public opposition to the wars in Iraq and Afghanistan, a stance shared by some medical colleagues but shaped for him by a growing religious fervor. The strands of religion and anti-war sentiment seemed to weave together in a PowerPoint presentation he made at Walter Reed in June 2007. In that presentation, Hasan argued that the Quran forbids Muslims to kill other Muslims, placing Muslim American troops in an impossible position. Such soldiers should be allowed to receive conscientious objector status, he concluded.

If they are not, he warned, there might be “;adverse events,”; citing the case of Sgt. Hasan Akbar, who was convicted of killing two soldiers in Kuwait and wounding 14 others by throwing grenades into their tents and then opening fire on them in 2003.

The presentation created a buzz among residents, some of whom were shocked and angered by what they thought was evidence of radical Islamist views. But other residents and faculty members said they considered it a useful analysis of the dueling pressures on Muslims in the American military, and some were wary of appearing insensitive toward Muslim culture.

For a master's program in public health, Hasan gave another presentation to his environmental health class titled, “;Why The War on Terror is a War on Islam.”; Some fellow students found it inappropriate and troubling, and at least one complained to the professor, former students said.

By 2008, some senior faculty members at Walter Reed were questioning not only Hasan's abilities as a psychiatrist, but also his loyalty to the country, according to people who know him. It is unclear if anyone took the concerns to senior military officials. Others argued that with the proper guidance, he could become not just a capable psychiatrist, but a valuable researcher for the Army, given his understanding of the pressures facing Muslim troops.

From March to May of this year, Hasan was sent back to work in an inpatient psychiatric ward at Walter Reed in what colleagues saw as a remedial stint. Lt. Eric Notkin, a nurse, often joined him on rounds, seeing many patients who had been evacuated from Iraq or Afghanistan after suicide threats or attempts.

“;The worst we saw were the patients who had shot themselves in the head or face and survived,”; Notkin said. “;They'd be stabilized and come to us.”;

Notkin grew fond of the quiet, unpretentious psychiatrist, who did not have a desk like other doctors and did his paperwork at a long table with nurses and technicians. After a trip to Israel, the nurse said, he recalled chatting with Hasan about the Israeli-Palestinian conflict, the Sept. 11 attacks and bias against Muslims. He detected no trace of radicalism.

Even at his mosque, Hasan formed no lasting friendships. Debbie Shankman, a non-Muslim who volunteers there, recalled spending an hour with him trying to calm a distraught woman who had just immigrated from India and spoke no English.

“;At the time he seemed intelligent, compassionate and willing to help,”; Shankman said. “;What I thought was odd is that he never spoke to me again.”;

A NEW LIFE AT FORT HOOD

In July, Hasan was sent to Fort Hood, the Army's largest post, a place bustling with the work of war and surrounded by all the scruffy trappings of an Army town: pawn shops and payday loan outlets, beer joints and tattoo parlors.

In his first weeks, Hasan seemed to be making long-term plans. He applied for a job as a liaison to Muslim soldiers. He printed up the business cards with his Fort Hood address for his moonlighting therapist job, permitted by Army rules as long as his superiors approved.

He became a regular at a Killeen mosque, frequently expounding on his view that Muslim soldiers should not be required to fight in Muslim lands. He prayed five times a day, people who knew him said. At some point, he learned he would be deployed to Afghanistan.

By September, Hasan had purchased a handgun and begun to visit the strip club next door to the gun shop. The club's general manager, Matthew Jones, said he stayed for six or seven hours the handful of times he visited, paying for lap dances in a private room.

The day before the shootings, Hasan began giving away belongings, including food, clothing and furnishings. To one neighbor, Patricia Villa, he gave two sport coats and a business suit still in a dry cleaning bag. “;You should sell these,”; he suggested. The rest, he said, should be given to the Salvation Army.

On the morning of the shootings, he stopped by the home of another neighbor, Lenna Brown, as she was sharing coffee with a friend. He gave them both brand new copies of the Quran and suggested that they read the verses on Maryam, Muhammad's rendering of the Virgin Mary story.

“;I asked him where are you going, and he said 'Afghanistan,' “; Brown said. She asked him how he felt about that, and he paused before answering.

“;I am going to do God's work,”; he replied.