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.

The fact that Harzi has been freed from detention "doesn't mean he's any less a suspect," the official said, adding Harzi does not appear on video taken of the Benghazi compound.

Investigators have identified at least 15 people who may be suspects, the official told CNN, indicating some were identified on the video.

"We will get indictments," the official said. "but it's not possible to put a timetable on it."

Reports on the attack

In December, an independent review of the Benghazi assault cited "systemic failures and leadership and management deficiencies" at the State Department.

Four State Department officials, including two who oversaw security decisions for Benghazi, were disciplined a day after the report was released.

Clinton got a copy of the report and said in letters to State Department chiefs that she accepted its recommendations to beef up security and intelligence gathering in high-threat areas.

Before the report came out, Clinton had popular approval ratings in nationwide polls.

A December Bloomberg National Poll showed 70 percent of Americans had a mostly favorable view of her. Polls from Politico/George Washington University, ABC News/Washington Post and the Siena College Research Institute also showed high marks.