Just hours before the attack, Stevens sent a message to the State Department that referred to a meeting nine days earlier during which the commander of Benghazi's Supreme Security Council "expressed growing frustration with police and security forces" about security capabilities.
That cable, since made public, is part of more than 160 pages of documents that paint a picture of persistent and unpredictable violence in and around Benghazi last year. It also reveals that the U.S. contingent in Benghazi felt it needed more security.
In February, the regional security officer in Tripoli, Eric Nordstrom, warned that having just two diplomatic security agents on the ground in Benghazi made movements outside the U.S. facility impossible.
"I've been placed in a difficult spot when the ambassador tells me I need to support Benghazi," Nordstrom wrote in a Feb. 12 email to the regional director of the Near East Affairs Department at the State Department.
Was Clinton informed about the rise of al-Qaida-linked militants?
In the Sept. 11 cable, a paragraph refers to the "expanding Islamist influence in Derna," a town east of Benghazi, amid reports linking "the Abu Salim Brigade with a troubling increase in violence and Islamist influence."
The Abu Salim Brigade was prominent among the opponents of former strongman Moammar Gadhafi.
The ambassador refers to another meeting on Sept. 9 in which commanders of unofficial militia claimed that the Libyan Armed Forces depended on them to secure eastern Libya, and even supplied them with weapons.
Communication from the ground up likely will be examined during Clinton's testimony.
'Talking points' cited by Rice and why didn't Clinton give that public explanation?
Rice spoke for the Obama administration on Sunday talk shows on Sept. 16. She made several claims that turned out to be wrong.
The primary complaint from Republicans is that Rice's remarks were centered on anger over the anti-Islam film, "Innocence of Muslims," when there was classified intelligence available suggesting a possible al-Qaida link.
On the talk shows, Rice spoke from unclassified talking points officials said were provided by the intelligence community. She said the armed assault was spontaneous and linked to regional outrage over the film.
Since then, Rice has twice talked to lawmakers about her remarks. In a statement, Rice said her talking points were "incorrect in a key respect: There was no protest or demonstration in Benghazi."
"While we certainly wish that we had had perfect information just days after the terrorist attack, as is often the case," the statement said. "The intelligence assessment has evolved."
Obama defended Rice publicly, but she later withdrew her name from consideration as his likely nominee to replace Clinton at the State Department.
Why has only one attack suspect been detained, and then released?
Ali Harzi was freed earlier this month by a Tunisian judge overseeing the case against him, the country's state news agency reported. He was arrested in Turkey in connection with the Benghazi attack. On Jan. 9, U.S. State Department spokeswoman Victoria Nuland referred questions to the FBI, which she said "has the lead on the Benghazi investigation."
The Tunisian news agency, TAP, reported that Harzi had been questioned by Tunisian authorities and the FBI "as a witness and not a suspect."
But a U.S. federal law enforcement official with direct knowledge of the probe said he remains a suspect.