U.S. Ambassador Chris Stevens and three other Americans were killed in an attack on the consulate in Benghazi on Sept. 11, 2012.
The report says the State Department had ignored its own "tripwires" set to determine when it had become too dangerous to operate in Benghazi, and continued to operate the facility there, despite a steady drumbeat of U.S. intelligence reports showing the danger was rising.
"The State Department should have increased its security posture more significantly in Benghazi based on the deteriorating security situation on the ground and IC threat reporting on the prior attacks against Westerners in Benghazi, including two previous incidents" at the temporary diplomatic facility that year, a summary of the report states.
The report even laid blame on the late Ambassador Stevens. The U.S. military was not positioned to aid the Americans in need, the report stated, and Stevens had twice rejected additional security offered by the head of Africa Command weeks before the attack.
In the aftermath of the attacks, the report states U.S. analysts confused policymakers by blaming the violence on protests without enough supporting intelligence.
"Intelligence analysts inaccurately referred to the presence of a protest at the U.S. mission facility before the attack based on open source information and limited intelligence, but without sufficient intelligence or eyewitness statements to corroborate that assertion," the report said, adding that the U.S. intelligence community then took too long to correct their error, "which caused confusion and influenced the public statements of policymakers."
The report recommended that the intelligence community expand its work to analyze social media used by extremists, noting that little of that was done before the attacks, and it's possible there were hints in web postings of trouble ahead.
The Associated Press contributed to this report.