Former U.S. Secretary of State Hillary Clinton told a Republican-led congressional committee Thursday that she had "lost more sleep than all of you put together" over the deadly 2012 attack on the U.S. consulate in Benghazi, Libya.
Clinton was the sole witness during the fourth congressional hearing on the attack that left four Americans dead, including U.S. Ambassador Christopher Stevens.
Republicans had alleged there were many inconsistencies in Clinton's account of what happened and what could have been done to prevent the incident. They also said previous investigations hadn't been thorough enough.
Specifically, Republicans wanted to know whether the attack on the compound was a planned terrorist strike that could have been stopped with proper security measures or was part of regionwide protests against videos mocking Islam.
The hearing began early in the morning and lasted well into the evening. Clinton at times looked bored and impatient, but answered the questions calmly, saying there could never be perfect security anywhere.
"America must lead in a dangerous world, and our diplomats must continue representing us in dangerous places,” she said. "We inevitably must accept a level of risk to protect our country and advance our interests and values."
While some Republicans have said Clinton rejected pleas from Stevens for more security in Benghazi, she said those requests never reached her desk and instead were left in the hands of security experts.
She denied telling then-Defense Secretary Leon Panetta to order Marines to stand down during the attack.
"Of course not ... logistics and distance made it unlikely they could be anywhere near Benghazi in a reasonable time," she said.
WATCH: Former Secretary of State Hillary Clinton testifies before the House Committee on Benghazi
There appeared to be wavering accounts by Obama administration officials in the days immediately following the Benghazi attack. Clinton said they were working with early strands of intelligence.
"There were probably a number of different motivations for the attack," she said. But after more than three years and numerous investigations, it is still unclear exactly why the militants attacked the consulate.
Clinton is the Democratic front-runner for the 2016 presidential election. Many Democrats accuse Republicans of holding the Benghazi hearings as a witch hunt to try to destroy her chance of becoming the next U.S. chief executive.
Democrats have seized on remarks made this month by House Majority Leader Kevin McCarthy during an appearance on a Fox News program. McCarthy appeared to boast that since House Republicans created the special committee looking into the attacks, Clinton's approval ratings have dropped.
South Carolina Republican Trey Gowdy, who chaired Thursday's hearing, made it clear at the very start that this was not his motive.
"Madam Secretary, I understand some people, frankly in both parties, have suggested this investigation is about you," he said. "Let me assure you, it is not."
Gowdy opened the hearing with a lengthy explanation about why the panel was needed and how it differed from other review boards. Questions lingered regarding the government's actions before and after the attacks, "because previous investigations were not thorough," he said.
Gowdy told Clinton the hearing was looking for the truth about the diplomatic compound's request for more security, equipment and personnel — and what was being discussed in Washington while the Americans were under attack.
House Benghazi Committee Chairman Rep. Trey Gowdy, R-S.C. listens as Democratic presidential candidate, former Secretary of State Hillary Clinton testifies before the committee on Capitol Hill, in Washington, Oct. 22, 2015.
Democratic Representative Elijah Cummings of Maryland, his party's ranking member on the committee, used his opening statement to criticize the panel, saying its work was politically motivated against Clinton.
"What is impossible is for any reasonable person to continue denying that Republicans are squandering millions of taxpayer dollars on this abusive effort to derail Secretary Clinton's presidential campaign," he said.
Cummings said the families of those killed in Libya asked the committee for three things: to avoid making the investigation a political football, find the facts, and make sure this sort of incident does not happen again.
Cummings and Gowdy at one point shouted at each other over whether to release previous closed-door testimony from close Clinton aide Sidney Bluementhal, who communicated with her via email about Libya.
The hallway outside the hearing room where former U.S. Secretary of State Hillary Clinton will testify Thursday before the Republican-led special House committee investigating the deadly 2012 attack on the U.S. consulate in Benghazi, Libya, in Washington.
The Benghazi panel was created in May 2014 after seven previous congressional probes into the attack. Democrats have called for the panel to be disbanded, saying it has not come up with any new information about Benghazi and is wasting taxpayer money. It has spent more than $4.5 million so far.
Security in Benghazi
During testimony, Clinton said the U.S. diplomatic outpost in Benghazi clearly wasn't provided with all the security requested by the ambassador and the mission.
But Clinton also testified that even critics of the Benghazi security level have said the type of attack that took place would have been difficult to repel.
Her comments came in response to committee member Martha Roby, an Alabama Republican, who quoted a review board’s report that found security was "grossly inadequate."
FILE - The U.S. Consulate in Benghazi, Libya burns during a September 2012 attack that killed the U.S. Ambassador and three others.
A 2012 report by a government accountability review board sharply faulted State Department officials for providing "grossly" insufficient security in Benghazi, despite upgrade requests from Stevens and others in Libya. A bipartisan Senate committee report said keeping the Benghazi mission open under those circumstances was "a grievous mistake."
Clinton said the Obama administration has tried to comply with the board’s recommendations.
The State Department pulled out of Benghazi immediately after the attack and left Libya altogether in 2014. The U.S. Embassy in Tripoli remains shuttered, the country still considered too unstable and dangerous for a return.
In late 2013, Clinton delivered sometimes-heated congressional testimony on the Benghazi attacks.
Some material for this report came from AP, AFP and Reuters.