Here is a look at the investigation in Washington of the attacks in Benghazi, Libya, three years ago, that killed four Americans, including Ambassador Chris Stevens.
Question: What happened in Benghazi?
Answer: The attack on the U.S. diplomatic compound in the Mediterranean port city in Libya occurred on September 11, 2012 – the 11th anniversary of the terrror attacks against the United States in 2001. The Benghazi attack came in three waves, spread over eight hours, at two locations. A few attackers who scaled the wall of the diplomatic post after dark opened a gate, allowing dozens of armed men inside. They set the building on fire. Ambassador Chris Stevens and Sean Smith, a State Department communications specialist, were overcome by choking smoke in a safe room; both later died.
Hours later, a nearby CIA annex was attacked twice. CIA security contractors Tyrone Woods and Glen Doherty died there while defending the annex from the rooftop. A team of six security officials summoned from Tripoli and a Libyan military unit helped evacuate the remaining U.S. personnel.
Q: What is the committee and what has happened in 17 months of investigative work?
A: The Select Committee on the Events Surrounding the 2012 Terrorist Attack in Benghazi, Libya (its official name), was created in May 2014 to investigate the causes of and responses to the two attacks.
Despite seven previous congressional investigations into Benghazi, House Speaker John Boehner alleged an administration coverup and called for the establishment of the committee.
The committee has spent $4.5 million on the probe so far, has interviewed dozens of witnessess and reviewed thousands of pages of documents. It is expected to continue its work into 2016 - a presidential election year - and will eventually produce a report on its findings.
As of this month, the Benghazi investigation has surpassed the length of the congressional investigation of the Watergate political scandal in the 1970s.
Q: What has been a recent criticism of the committee?
A: Committee Chairman Trey Gowdy has been forced to defend the panel in recent weeks, especially after several fellow Republicans suggested the panel's real aim was to discredit Clinton's presidential ambitions.
Q: Whad did Clinton say in her previous Congressional testimony in Congress?
A: In January 2013 she testified for more than five hours before two congressional committees. She rejected suggestions from Republican lawmakers that the Obama administration tried to mislead the country about the full circumstances of the attack. Clinton did take responsibility for missteps and failures by the State Department to increase security for American staff in Libya and to anticipate the attack.
In a contentious moment, Clinton said then that she was more focused on how to improve security, and that it did not matter what specific event may have triggered the attack.
Q. What questions does Clinton likely face about Benghazi Thursday?
A. Committee members are likely to ask Clinton about the security conditions in Benghazi and whether the State Department considered the consulate workers' safety, considering that other foreign diplomatic missions, including Britain's, had abandoned their facilities in their area.
Q: Has anyone been apprehended in connection with the attack?
A: Ahmed Abu Khattala was captured in June 2014 by U.S. special forces and brought to the United States to face trial. Khattala, 43, is the first militant to be prosecuted for the Benghazi violence. He initially was charged with conspiracy to provide support to terrorists and multiple other counts that make him eligible for the death penalty if convicted.
Q: What has happened in Benghazi, and Libya, in the past three years?
A: Despite hopes that a democratic system would emerge following the 2011 revolt against dictator Moammar Gadhafi, Libya has steadily spiraled into chaos and violence involving a myriad of armed factions.
The North African state now has two rival governments, with two parliaments and even two state oil companies. Each is backed by a loose coalition of armed forces, mostly inspired by local or tribal loyalties rather than any concept of the state.
For a year, the capital, Tripoli, has been held by Libya Dawn, an armed alliance of former rebels from the city of Misrata and Islamist-leaning brigades who have set up their own self-styled government and reinstated the former parliament.
The country's internationally recognized government and elected parliament work in eastern Libya, backed by a loose network of armed factions including a divisive former Gadhafi ally, General Khalifa Haftar.
Some material for this report came from AP and Reuters.