Soon after the killings, witnesses said that Maj. Nidal Malik Hasan, the alleged gunman, had shouted "Allahu Akbar," the Arabic phrase for "God is great," as he fired.
Meanwhile, a video played repeatedly on cable television of him wearing the white dishdasha and skullcap of an observant Muslim.
The clip was recorded just hours before the attack that killed 13 people and wounded at least 28 others, reports said.
For those who believe Muslims and Arab-Americans -- Hasan's parents were Palestinian -- constitute a dangerous "fifth column," the tragedy provided further evidence.
Fox News host Brian Kilmeade suggested that all Muslim Army officers should face special debriefings. "If I'm going to be deployed in a foxhole, if I'm going to be sticking in an outpost," he said, "I got to know the guy next to me is not going to want to kill me."
Similar rhetoric was heard two years ago when the U.S. Military Academy at West Point dedicated its first Muslim prayer room. Investor's Business Daily criticized the Army for "a show of blind tolerance" that increased the chances of "Islamist infiltration."
Some of the suspicions about Muslims in uniform arose after Army Sgt. Hasan Akbar, an African-American convert to Islam, killed two officers and wounded 14 others in a grenade attack in Kuwait a few days before the 2003 U.S. invasion of Iraq. Akbar, who was later sentenced to death by a military court, said he was upset that U.S. troops planned to kill his fellow Muslims.
Relatives of Hasan, a psychiatrist about to be deployed to Afghanistan, said he was often harassed for being a Muslim after the Sept. 11, 2001, terrorist attacks and wanted to leave the military.
The Pentagon says there are 3,546 self-identified Muslims in the military. Muslim groups say there as as many as 15,000 because many list no religious preference in their records. Hasan is among nearly 300,000 of 1.4 million active-duty service members who didn't list a religion.
Ray Hanania, a Chicago radio talk show host and co-founder of the Association of Patriotic Arab Americans in Military, condemned Hasan's alleged actions as the work of a troubled individual.
But he said many Arab-American and Muslim service members can tell stories of prejudice in the ranks.