While CIA operatives showed heroism during the rescue, the agency failed to properly vet beforehand the February 17 Martyr’s Brigade, a local militia comprised in part by Islamist fighters who had fought against Libyan dictator Muammar Gadhafi during the 2011 revolution. The State Department’s own Accountability Review Board (ARB) found most members of the brigade—one of the best armed militias in eastern Libya, with a membership in the low thousands—failed to show up on the evening of the attacks, despite agreeing to be the compound’s “quick reaction force,” intended to perform the role of the Libyan state in a city that lacked mature security institutions.

After the attack began, brigade members declined CIA security officers attempts to join them in mounting a rescue mission, according to the ARB—which also found that three Brigade members who were stationed that evening at the compound failed to provide advanced warning that a mob of attackers with bad intentions was approaching the embassy that night, leaving the five U.S. diplomatic security officers at the compound little time to prepare a defense.

The CIA’s failure to properly vet the February 17 Martyr’s Brigade has not been disclosed by the ARB or an interim report by House Republicans released last month.