Two officials speaking on condition of anonymity because they were not authorized to discuss the case on the record said the Washington-based joint terrorism task force overseen by the FBI was notified of communications between Hasan and a radical imam overseas, and the information was turned over to a Defense Criminal Investigative Service employee assigned to the task force.
That worker wrote up an assessment of Hasan after reviewing the Army major's personnel file and the communications. The assessment concluded Hasan did not merit further investigation, in large part because his communications with the imam were centered on a research paper he was writing at the time, and the investigator had concluded Hasan was in fact working on such a paper, the officials said.
In hindsight, critics question whether the government too quickly dismissed Hasan as a threat, reports CBS News correspondent Bob Orr.
"Did they reach a conclusion, you know, based on just an overview and a cursory view of the evidence and said, 'we don't have to worry about this guy?'" asked Rep. Peter Hoekstra, R-Mich.
Washington Unplugged: Hoekstra's Fort Hood Frustrations
The disclosure came as questions swirled about whether opportunities were missed to head off the massacre - 13 dead and 29 wounded - and the FBI launched its own internal review of how it handled the early information about Hasan. Military, law enforcement and intelligence agencies are all defending themselves against tough questions about what each of them knew about Hasan before he allegedly opened fire in a crowded room at the huge military base in Texas.
Within hours after the role of the defense investigator on the task force was disclosed, a senior defense official said "based on what we know now, neither the U.S. Army nor any other organization within the Department of Defense knew of Maj. Hasan's contacts with any Muslim extremists."
CBSNews.com Special Report: Tragedy at Fort Hood
This defense official was not authorized to discuss the case on the record and spoke on condition of anonymity.
Hasan, awake and talking to doctors, met his lawyer Monday in the San Antonio hospital where he is recovering, under guard, from gunshot wounds in the assault. He has not been formally charged but officials plan to charge him in military court, not a civilian one, a choice that suggests his alleged actions are not thought to have emanated from a terrorist organization.
Investigators still believe Hasan acted alone, despite his communications with Anwar al-Awlaki, an imam released from a Yemeni jail last year who has used his personal Web site to encourage Muslims across the world to kill U.S. troops in Iraq. But, officials deemed the communications "benign" and the FBI concluded Hasan presented no imminent threat, reports Orr.
Investigative officials spoke on condition of anonymity because they were not authorized to discuss the case on the record. Republican Rep. Pete Hoekstra of Michigan, the top Republican on the House Intelligence Committee, said it was his understanding Hasan and the imam exchanged e-mails that counterterrorism officials picked up.
Meanwhile, The Washington Post reported Tuesday that Hasan warned his medical colleagues a year and a half ago that to "decrease adverse events" the U.S. military should allow Muslim soldiers to be released as conscientious objectors instead of fighting in wars against other Muslims. Hasan made the recommendation in a culminating presentation to senior Army doctors at Walter Reed Medical Center, where he spent six years as an intern, resident and fellow before being transferred to Fort Hood.
Washington Post Slideshow: Hasan's Presentation on Islam
FBI Director Robert Mueller ordered the inquiry into the bureau's handling of the case, including its response to potentially worrisome information gathered about Hasan beginning in December 2008 and continuing into early this year.
Authorities revealed the major had once been under scrutiny from a joint terrorism task force because of the series of communications going back months. Al-Awlaki is a former imam at a Falls Church, Va., mosque where Hasan and his family occasionally worshipped.
In 2001, al-Awlaki, a native-born U.S. citizen, had contact with two of the Sept. 11 hijackers, and on Monday his Web site praised Hasan as a hero.
Military officials were made aware of communications between Hasan and al-Awlaki, but because the messages did not advocate or threaten violence, civilian law enforcement authorities could not take the matter further, the officials said. The terrorism task force concluded Hasan was not involved in terrorist planning.
Officials said the content of those messages was "consistent with the subject matter of his research," part of which involved post-traumatic stress disorder stemming from U.S. combat operations in Iraq and Afghanistan.
A law enforcement official said the communications consisted primarily of Hasan posing questions to the imam as a spiritual leader or adviser, and the imam did respond to at least some of those messages.
No formal investigation was ever opened based on the contacts, the officials said.
The most serious charge in military court is premeditated murder, which carries the death penalty.
More Coverage of the Tragedy at Fort Hood:
Counseling for Trauma, Grief at Ft. Hood
Ft. Hood Shooting: Composure Under Fire
Report: U.S. Knew Hasan Sought al Qaeda
Radical Imam's Web Site Praises Hasan
Fort Hood Reflects, but Work Carries On
Hasan Computer Shows No Terror Ties
List of Fort Hood Dead, Wounded