The report concluded that both the Defense Department and the FBI had sufficient information to detect that Army Maj. Nidal Malik Hasan had been radicalized to violent extremism, but they failed to understand and act on it. It said the FBI's top leaders must exercise more control over local field offices and put to better use the intelligence analysts who should have been able to connect the dots.
Hasan is charged with 13 counts of premeditated murder and 32 counts of attempted premeditated murder in the November 2009 shooting rampage at the Fort Hood military post.
Hasan is in custody, and a mental health evaluation has just been completed. A brigade commander who received the report is expected to make a recommendation next month on whether Hasan should stand trial and face the death penalty. A commanding general will make the final decision.
Complete Coverage: Tragedy at Fort Hood
"Our report's painful conclusion is that the Fort Hood massacre could have, and should have, been prevented," said Sen. Joseph I. Lieberman, an independent, calling it a heartbreaking tragedy of errors.
Many of the report's criticisms have been aired over the past year in other investigations of shooting. The Senate report stresses that the FBI's move to become more intelligence-driven has been hampered by internal conflicts that must be addressed.
And it says the bureau's failure to use its analysts well contributed to it overlooking the significance of communications with known terrorists transmitted by Hasan.
A joint terrorism task force overseen by the FBI learned late in 2009 of Hasan's repeated contact with U.S.-born radical cleric Anwar al-Awlaki, who encouraged Muslims to kill U.S. troops in Iraq. The FBI has said the task force did not refer early information about Hasan to superiors because it concluded he wasn't linked to terrorism.
The Senate report was released Thursday by Lieberman, chairman of the Senate Homeland Security and Governmental Affairs Committee, and its top Republican, Sen. Susan Collins. It is being delivered to the president and the heads of the FBI, Defense Department and Department of Homeland Security.
It charges that evidence of Hasan's radicalization was "on full display" to his superiors, and that an instructor and colleague "each referred to Hasan as a 'ticking time bomb,"' but no action was taken to discharge him and his evaluations were sanitized.
"This is not a case where a lone wolf was unknown to the FBI, unknown to the military officials, until he struck," said Collins.
More broadly, the report said that the Pentagon has failed to make necessary changes to identify violent Islamic extremism as a danger so that commanders will more readily watch for it and discharge service members who express those views.
Military supervisors, the report said, had the authority to discipline or discharge Hasan. But it concluded that the Defense Department did not inform or train commanders about how to recognize someone radicalized to Islamic extremism or how to distinguish that from the peaceful practice of Islam.
The enemy Islamist extremists must be labeled correctly and explicitly, the report said, in order for the military to counter the extremism.
Asked for comment on the Senate report's criticism, an Army spokesman said the Army will continue to make adjustments.
"We will closely examine the report's findings and recommendations," said Col. Tom Collins. "The Army has already implemented numerous concrete actions that have made our soldiers, families and civilian employees safer. There is still more work to do, but the Army is committed to doing all we can to learn from this tragic event."
The FBI, in a written statement, said it agrees with much of the report and had already identified several of the same areas of concern during an internal review and made changes. The FBI also noted that the report acknowledged the bureau's progress in disrupting terrorist plots by homegrown extremists.