WASHINGTON - President Barack Obama heads to Texas on Tuesday to remember the victims of last week's mass killing at the Fort Hood military base as chilling new details emerge about the prime suspect's possible terrorist ties and sympathies.

ABC News reported Monday that U.S. intelligence agencies were aware months ago that Nidal Malik Hasan, an Army psychiatrist, was attempting to make contact with people associated with al-Qaida, the extremist Muslim group that masterminded the 9-11 terrorist attacks on the United States eight years ago.

Citing two sources, ABC reported said it wasn't yet known if the intelligence agencies had informed the Army that one of its majors was reaching out to al-Qaida.

Hasan is in a Texas hospital recovering from the injuries he suffered during the carnage at Fort Hood that left 13 people dead and dozens more wounded. He is reportedly breathing on his own and talking, though it was unclear Monday whether he'd yet spoken to investigators.

Retired Col. John Galligan was retained by Hasan's family earlier in the day, and was heading to Texas to talk to him. Galligan said he'd asked investigators to refrain from questioning his client right now.

"We want to make sure that all of his rights, under the law, are protected," Galligan said.

In a country where the 9-11 attacks remain a gaping wound on the national psyche, some are arguing that Hasan's alleged crime amounts to yet another terrorist assault against the United States, and was not the act of a man simply depressed about his upcoming deployment to Afghanistan.

The Obama administration, Army and law enforcement officials, meanwhile, have cautioned against any rush to judgment about motive and say they're conducting a thorough investigation.

"We are going to take a very hard look at ourselves and look at anything that might have been done to have prevented this," Lt.-Gen. Bob Cone, the base commander at Fort Hood, told a news conference on Monday.

In addition to the alleged al-Qaida ties, investigators are also looking into whether Hasan, 39, maintained contact with a radical mosque leader from Falls Church, a town in northern Virginia near Washington. Anwar al Awlaki now lives in Yemen and runs a website that promotes worldwide jihad against the United States.

In a blog posting early Monday entitled "Nidal Hasan Did the Right Thing," Awlaki calls Hasan a "hero" and a "man of conscience who could not bear living the contradiction of being a Muslim and serving in an army that is fighting against his own people."

Hasan, born and raised in the United States, reportedly attended the Falls Church mosque when Awlaki was the imam there. The Telegraph of London reported that Awlaki once made contact with two of the 9-11 hijackers.

Hasan's relatives have said that the Army psychiatrist was despondent about his upcoming deployment to Afghanistan and had asked for a discharge, but was denied. They also say he was harassed by some of his colleagues for being a Muslim in the aftermath of 9-11, although the Army says it has no record of any complaints from Hasan about such harassment.

On Sunday, Army Chief of Staff George Casey warned 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," Casey said.

Government sources have said an initial review of Hasan's computer use has found no evidence of links to terror groups or anyone who might have helped plan or push him toward the attack. The review of Hasan's computer is continuing, one official said.

Hasan will likely face military justice rather than federal criminal charges if investigators determine the violence was the work of just one person.

Sen. Joseph Lieberman, the chairman of the Senate's homeland security committee, has called for an investigation into whether the Army missed signals that Hasan was an Islamic extremist.

"If Hasan was showing signs, saying to people that he had become an (Islamic) extremist, the U.S. Army has to have a zero tolerance," Lieberman said Sunday.

An aspiring senator went far further, accusing Obama of a "cover-up" due to his own Muslim background. The president's father was a Kenyan Muslim, but Obama was born in the United States and raised by his Christian mother and grandparents.

A statement from Andy Martin, a Republican Senate candidate from Illinois, said that Obama's Muslim "family history and overtures to the Muslim world may be endangering America's national security."

"Our first priority must be to protect our men and women in uniform from domestic extremists. Period," Martin said.

"Army intelligence failed. The FBI failed. We need leadership, not evasion and stand-pat excuses, from the Army and from the Obama administration."

Obama and the first lady, Michelle Obama, will attend a memorial service Tuesday for the 13 people killed in the shooting. The president is delaying the start of a trip to Asia to attend the event.

In the days since the bloody rampage at Fort Hood, some increasingly startling allegations have been made about Hasan, who allegedly shouted "God is great" in Arabic -- a phrase considered a jihadist battle cry -- as he opened fire.

Among the allegations made by Hasan's former colleagues to various media outlets:

-- That he once said Muslims should rise up against the U.S. military;

-- That he repeatedly expressed sympathy for suicide bombers;

-- That he was pleased by the recent death of an army recruiter, allegedly at the hands of a Muslim convert in Arkansas;

-- That he publicly called for the beheading or burning of non-Muslims, saying, "if you're a non-believer the Koran says you should have your head cut off, you should have oil poured down your throat, you should be set on fire."

-- That his eyes "lit up" when he mentioned his deep respect for Awlaki's teachings, according to a fellow Muslim officer at Fort Hood.