WASHINGTON — The killing of 13 people at Fort Hood, Texas, by an Army psychiatrist who is a Muslim has set off a rancorous debate that once again spotlights the fear among Muslims in America that they'll be collectively found guilty for the actions of one man.

Vitriolic exchanges have filled Internet sites devoted to military affairs, with some posters arguing that Muslims should be barred from the armed services.

News reporters deluged the mosque in Silver Spring, Md., where the Fort Hood shooting suspect once worshipped, demanding to know what the Quran, Islam's holy book, has to say about such events. One reporter asked if the suspect, Army Maj. Nidal Malik Hasan, who was born in Virginia and lived his whole life in the U.S., spoke with an accent.

Anita Husseini, who also worships at the Muslim Community Center, said that although she didn't know Hasan, she knew that what he's accused of doing would affect her life and those of others.

"My heart cried last night," said Husseini, a hairdresser. "Every time the Muslims try to get up, something goes 'boom' and pushes us back. What a crazy person decides does not define me or Islam."

"They're trying so hard to pin this on Islam," said Arshad Qureshi, the mosque's chairman. "They're working so hard to make it about religion."

U.S. military officials repeated Friday that the motive behind Thursday's shooting remained unclear. Hasan remains unconscious after a civilian police officer shot him four times.

Investigators seized his computer after news reports said that someone named Nidal Hasan had posted messages comparing suicide bombing missions to Japanese kamikaze pilots.

Lt. Gen. Robert W. Cone, the base commander at Fort Hood, said that witnesses to Thursday's mayhem reported that Hasan had shouted "Allahu Akbar," or "God is great" in Arabic, as he opened fire with two handguns on clusters of soldiers who were waiting for medical examinations and other processes in the sprawling base's Soldier Readiness Processing Center. The phrase is a traditional Muslim invocation.

Cone and others, however, turned away questions about Hasan's religion, and Cone said there was no evidence that Hasan was part of a wider plot.

Maj. Gen. Kevin Bergner, a Pentagon spokesman, said there was no doubt within the military hierarchy of the loyalty of Muslim service members. He said the armed forces would take steps to make sure "everyone is treated with dignity and respect."

Posters to Facebook and participants in chat rooms and popular military sites were less circumspect, revealing a bitterness that Muslims say they've often felt since the terrorist attacks of Sept. 11, 2001.

One Facebook page was titled "Against muslims in military! ... or in presidency" — a reference to the false claims that President Barack Obama is a Muslim.

One poster said he agreed with banning Muslims from the military.

Another commenter wrote: "Whoever you are, you're an idiot. It's a shame you weren't at Ft. Hood."

Muslims make up less than 0.3 percent of America's active duty military forces. Of the roughly 548,000 soldiers in the U.S. Army, about 2,500 are Muslims, 1,500 of them on active duty. By comparison, 105,000 claim Roman Catholicism as their religion, and 99,000 say they're Baptists. More than 1,800 soldiers say they're Jewish, surpassed by the nearly 2,500 who identified themselves as atheists. More than 101,000 list no religious affiliation.

That was the case with Hasan, according to Pentagon officials, even though interviews at the Silver Spring mosque make it clear that he was an observant Muslim who prayed daily — and often in uniform.

Mona Ayad, the administrative assistant at the center, said Hasan would come to prayer quite often, volunteer at the mosque, contribute money for the poor as Islam requires and answer phones.

He wasn't a loner, but he wasn't particularly social either. He stopped coming over the summer, apparently when he was transferred to Fort Hood.

Imam Mohamed Abdullahi Sheikh Mohamed, the mosque's chief cleric, said he knew Hasan from his frequent appearances at the mosque and knew he was a military doctor. However, he said, Hasan never brought up his work with the armed forces.

"He was not violent; he seemed calm. ... I was shocked," Mohamed said. "It's absolutely unacceptable what he did. ... He was a doctor. He was supposed to help people."

Hasan's religious affiliation was known to his military colleagues and may have caused tension.

Hasan's family said that he was harassed for his faith, and the Washington Post quoted his aunt Friday as saying Hasan had sought legal help in an effort to get out of the Army. On Friday, there were other reports that another soldier at Fort Hood had scratched his car with a key, causing about $1,000 in damage, and that someone removed a bumper sticker that read "Allah is Love."

Khallid Shabbaz, one of the Army's six Muslim chaplains, said in a television interview Thursday that he had talked to Hasan recently about becoming a Muslim chaplain, but Shabbaz didn't explain why he didn't choose Hasan.

One Army chaplain talked on the condition of anonymity out of fear that an interview would turn Thursday's shooting into a religious issue.

The chaplain said that some Muslims are conflicted about honoring their duty while fighting other Muslims in Iraq and Afghanistan. In those cases, Muslim soldiers usually prefer talking to a Muslim chaplain, he said. They also more often turn to Muslim chaplains when they feel harassed in the military.

The chaplain said that many of the soldiers he talked to felt betrayed mainly because Hasan was a fellow soldier.

"This is not a Muslim issue. It is a soldier issue. It is a punch in the gut," he said.

The chaplain said Muslim soldiers most commonly asked for help finding a place to worship where they serve. Some mosques, he said, don't want to serve soldiers.

Others ask about the Christian faith to better understand their comrades; Christian soldiers often ask about Islam as well, either to understand the communities they're fighting in or the soldiers with whom they're serving.

At the Muslim Community Center where Hasan prayed for five years, congregants, the imam and board members were deluged Friday with different versions of the same question:

"Does Islam condone this?"

Qureshi, the mosque's chairman, spent Friday morning and most of the afternoon telling reporters that Islam is a religion of peace. Multiple times, he was asked to explain why Hasan would do something like this.

By 2 p.m., he was tired. He'd seen Hasan come to the mosque and pray, but he had no idea why the man would open fire at an army base.

"We've been here 35 years quietly. We're just as American as everybody else," Qureshi said.

"It's a tragedy, and we're so sad about it," said Ayad, the administrative assistant. "But it doesn't have anything to do with us or Islam. … I wish we could separate ourselves from this tragedy."

In his sermon Friday, Mohamed paid his condolences to the families of the people who had been killed. He quoted a verse from the Quran that says taking one innocent life is like killing humankind.

"I ask the media people not to relate all the time everything to Islam," he said over loudspeakers.

The phone calls kept coming. "It's the L.A. Times," Ayad would say to anyone in the room. "It's CNN."

"This is just a nightmare," she said as she hung up the phone. "He's the person that you'd least expect, from what I've seen of him."