This account of the CIA presence in Benghazi sheds new light on the events, and how the essentially covert nature of the U.S. operations there created confusion. Congressional investigators say it appears that the CIA and State Department weren't on the same page about their respective roles on security, underlining the rift between agencies over taking responsibility and raising questions about whether the security arrangement in Benghazi was flawed.

The CIA's secret role helps explain why security appeared inadequate at the U.S. diplomatic facility. State Department officials believed that responsibility was set to be shouldered in part by CIA personnel in the city through a series of secret agreements that even some officials in Washington didn't know about.

It also explains why the consulate was abandoned to looters for weeks afterward while U.S. efforts focused on securing the more important CIA quarters. Officials say it is unclear whether the militants knew about the CIA presence or stumbled upon the facility by following Americans there after the attack on the consulate.