FORT HOOD, Texas -- A key U.S. senator said yesterday he would begin an investigation into whether the Army missed signs that the man accused of opening fire at Fort Hood had embraced an increasingly extremist view of Islamic ideology.

Sen. Joe Lieberman's call for an investigation into the Thursday shootings that killed 13 and wounded 29 came a day after classmates who participated in a 2007-2008 master's program at a military college said they complained to superiors about Maj. Nidal Malik Hasan and what they considered to be his anti-American views, which included his giving a presentation that justified suicide bombing and telling classmates that Islamic law trumped the U.S. Constitution.

"If Hasan was showing signs, saying to people that he had become an Islamist extremist, the U.S. Army has to have zero tolerance," Mr. Lieberman, an independent from Connecticut, said on "Fox News Sunday." "He should have been gone."

Mr. Lieberman, chairman of the Senate Homeland Security and Governmental Affairs Committee, wants Congress to determine whether the shootings constitute a terrorist attack.

The Army chief of staff, Gen. George Casey, also warned yesterday against reaching conclusions about the suspected shooter's motives until investigators have fully explored the attack. "I think the speculation [on Hasan's Islamic roots] could potentially heighten backlash against some of our Muslim soldiers," he said on ABC's "This Week."

Dr. Val Finnell told The Associated Press on Saturday that he and other classmates participating in a 2007-2008 master's program with Maj. Hasan at the Uniformed Services University complained about his comments, including that the war on terror was "a war against Islam."

Meanwhile, the FBI will probably look into whether Maj. Hasan attended the same Virginia mosque as two Sept. 11 hijackers in 2001 at a time when a radical imam preached there, said a law enforcement official who spoke on condition of anonymity because the investigation is ongoing.

Imam Johari Abdul-Malik, outreach director at the Dar al Hijrah Islamic Center, confirmed yesterday that Maj. Hasan's family participated in services at the mosque in Falls Church, Va. Mr. Abdul-Malik said the Hasans were not leaders at the mosque and their attendance was utterly normal, and he did not know whether Maj. Hasan himself ever attended services there.

In 2001, Anwar Aulaqi was an imam, or spiritual leader, at the mosque. Mr. Aulaqi told the FBI in 2001 that before he moved to Virginia in early 2001, he met with 9/11 hijacker Nawaf al-Hazmi several times in San Diego. Mr. Hazmi at the time was living with Khalid al-Mihdhar, another hijacker. Mr. Hazmi and another hijacker, Hani Hanjour, attended the Dar al Hijrah mosque in early April 2001.

Faizul Khan, former imam of the Muslim Community Center in nearby Silver Spring, Md., where Maj. Hasan also worshipped, said he was not aware that Maj. Hasan had attended services at Dar al Hijrah but said it would not be unusual for Maj. Hasan to attend more than one mosque concurrently. Mr. Khan said he did not recall Maj. Hasan mentioning having been taught or preached to by Mr. Aulaqi.

Authorities continue to refer to Maj. Hasan, 39, as the only suspect in the shootings that killed 13 and wounded 29. Maj. Hasan, who was shot by civilian police, was in critical but stable condition at an Army hospital in San Antonio.

Washington correspondent Daniel Malloy writes the "Pittsburgh On The Potomac" blog exclusively at PG+, a members-only web site of the Pittsburgh Post-Gazette. Our introduction to PG+ gives you all the details.