Fort Hood, Texas (CNN) -- Maj. Nidal Malik Hasan, the suspect in last week's massacre at Fort Hood in Texas, was conscious and talking at a military hospital Monday while the Army probed whether it missed any signs that could have prevented the killings.
Hasan, an Army psychiatrist who worked at a Fort Hood hospital, remained in intensive care at Brooke Army Medical Center in San Antonio, Texas.
Authorities have not identified a motive in Thursday's attack, which left 13 dead and 42 others wounded. But Lt. Gen. Robert Cone, Fort Hood's commander, told reporters he has ordered his officers to "immediately take a hard look and make sure if there's anybody out there struggling."
"Hasan was a soldier and we have other soldiers ... that might have some of the same stress and indicators that he has," Cone said. "We have to look across our entire formation, not just in a medical community but really look hard to our right and left. That's the responsibility for everybody from the top to the bottom to make sure we're taking care of our own."
Video: Fort Hood's wounded speak 
Video: Army unites after massacre 
Video: Backlash against Muslims? 
Video: Getting to know the suspect Army officials have voiced concern about jumping to any conclusions about the motive, warning about a possible backlash against Muslim soldiers. Several witnesses, like Pvt. Robert Foster, who was wounded in the hip during the attack, reported Hasan shouted "Allahu Akbar" -- Arabic for "God is great" -- which Islamic terrorists have used as a battle cry.
"I was sitting in about the second row back when the assailant stood up and yelled 'Allah Akbar' in Arabic and he opened fire," Foster, 21, said Monday on CNN's "American Morning."
Foster said he wasn't sure "Allahu Akbar" was exactly what Hasan said, noting that "with that much adrenaline, you tend to forget things."
The Army leadership at Fort Hood will "take a very hard look at ourselves and look at anything that might have been done to have prevented this," Cone said Monday.
"I think what we're looking for are sort of people with overwhelming personal problems and patterns of behavior that are not at all related to religion."
But other investigators have been examining whether Hasan had any ties to Islamic radical groups or individuals -- in particular, a former cleric at a mosque Hasan attended when he lived in Virginia.
U.S. military officials said intelligence agencies intercepted communications between Hasan and Anwar al-Awlaki, a former imam at the Dar Al-Hijrah Islamic Center in Falls Church, a suburb of Washington. Al-Awlaki, who left the United States in 2002 and is believed to be living in Yemen, was the subject of several federal investigations dating back to the late 1990s, but was never charged.
Intelligence agencies intercepted communications from Hasan to al-Awlaki and shared them with other U.S. government agencies, U.S. military officials told CNN on Monday. Federal authorities dropped the inquiry into Hasan's communications after deciding that the messages warranted no further action, one of the officials said.
In a statement issued Monday night, the FBI said one of its Joint Terrorism Task Forces -- which included Pentagon, state and local investigators -- "assessed that the content of those communications was consistent with research being conducted by Maj. Hasan in his position as a psychiatrist at the Walter Reed Medical Center [in Washington]."
"Because the content of the communications was explainable by his research and nothing else derogatory was found, the JTTF concluded that Maj. Hasan was not involved in terrorist activities or terrorist planning," the FBI said.
FBI Director Robert Mueller has ordered a review of the matter, but the probe so far "indicates that the alleged gunman acted alone and was not part of a broader terrorist plot," the FBI said.
An online post attributed to al-Awlaki praised Hasan as a hero for the Fort Hood attack, saying he "could not bear living the contradiction of being a Muslim and serving in an army that is fighting against his own people."
The Dar Al-Hijrah mosque denounced al-Awlaki's remarks, and its current imam said he was stunned to hear Hasan was the suspect in the rampage.
"The quiet, very peaceful person coming in and out of the mosque, I couldn't believe he could have done this," Sheikh Shaker Elsayed told CNN.
The 39-year-old Hasan, a U.S.-born citizen of Palestinian descent, was a licensed psychiatrist who joined the Army in 1997. He was promoted to major in May and was scheduled to deploy to Afghanistan sometime soon, but had been telling his family since 2001 that he wanted to get out of the military.
He told his family he had been taunted after the terrorist attacks of September 11, 2001, and reported to police in August that his car was keyed and a bumper sticker that read "Allah is Love" was torn off. A neighbor was charged with criminal mischief after that complaint.
Hasan had a late November deployment date to Afghanistan, Fort Hood spokesman Col. John Rossi said. It was to have been Hasan's first overseas deployment.
Hasan was wounded several times during the attack at Fort Hood's processing center, where soldiers report before they head to war.
His ventilator was removed over the weekend, and he began talking afterwards, hospital spokesman Dewey Mitchell said.
Hasan is speaking with hospital staff, said Mitchell, who was unable to say whether Hasan had been speaking with Army investigators.
U.S. Sen. Joe Lieberman said he plans to launch a Senate committee hearing into whether the shootings were a terrorist act and if the Army should have taken pre-emptive steps in response to reported signs of Islamic extremism by Hasan.
If Hasan was showing signs of being an Islamic extremist, the Army should have acted on that earlier and "he should have been gone," said Lieberman, a Connecticut independent and chairman of the Senate Homeland Security and Governmental Affairs Committee, told "Fox News Sunday."
President Obama will speak at Tuesday's memorial service for the shooting victims at Fort Hood, and will meet with victims' families, his spokesman said.
"The president will meet with families of those that lost a loved one last week, as well as speak to the larger memorial that will take place at the base," White House Press Secretary Robert Gibbs said in his daily briefing Monday.
First lady Michelle Obama will accompany the president on the trip, Gibbs said.
Defense Secretary Robert Gates will also participate in the memorial service, but he will not speak, Pentagon spokesman Geoff Morrell said.
CNN's Brian Todd, Pam Benson, Mike Mount, David Mattingly and Pam Benson contributed to this report.
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