A report released Friday says that commanders must be encouraged to look for cues that could prevent a similar attack.
"The report raises serious questions about the degree to which the entire Department of Defense is prepared for similar incidents in the future, especially multiple simultaneous incidents," Defense Secretary Robert Gates said.
According to two officials familiar with the case, as many as eight Army officers could face discipline for failing to do anything when Hasan displayed erratic behavior early in his military career. The officials spoke on condition of anonymity because that information has not been publicly released.
Hasan, 39, is accused of murdering 13 people on Nov. 5 at Fort Hood, the worst killing spree on a U.S. military base.
Retired Adm. Vernon E. Clark and former Army secretary Togo D. West Jr., who led the investigation, told reporters that there were discrepancies between Hasan's performance and his personnel records.
Their investigation also found that his top-level security clearance hadn't been properly investigated. Had policies been properly followed, investigators say his clearance may have been revoked "and his continued service and pending deployment would have been subject to increased scrutiny."
A separate White House assessment concluded that the Defense and Justice departments should improve communications on "disaffected individuals." It also found that intelligence and law enforcement personnel should conduct a more thorough analysis of certain information, according to a summary released Friday.
Gates said the findings were unacceptable and directed Army Secretary John McHugh to put new procedures in place by summer.
"It is clear that as a department we have not done enough to adapt to the evolving internal security threat" and the military "is burdened by 20th century processes and attitudes mostly rooted in the Cold War," Gates said.
Officials say that several midlevel officers overlooked or failed to act on red flags in Hasan's lax work habits and his fixation on religion. Hasan was seen by the reviews as a loner who was passed along from office to office and job to job despite professional failings that included missed or failed exams and physical fitness requirements.
Findings about Hasan and those who supervised him are contained in a confidential addendum to a larger report about the Pentagon's handling of potential extremism in the ranks and readiness to handle the sort of mass casualties Hasan allegedly inflicted.
The officers supervised Hasan when he was a medical student and during his early work as an Army psychiatrist at Walter Reed Army Medical Center in Washington.
The report, called "Protecting the Force," concludes that the Defense Department had outdated and ineffective means to identify threats from inside as opposed to outside the military. It also says the department's means of sharing and collating information about a potential troublemaker are inadequate, one official said.