"Was it because of a protest or was it because of guys out for a walk one night decided they'd go kill some Americans? What difference, at this point, does it make? It is our job to figure out what happened and do everything we can to prevent it from ever happening," she said.

4. Militants in Mali and Algeria have arms from Libya

Clinton warned the security situation in northern Mali, where international forces are battling militants, has been exacerbated by flow of weapons from neighboring Libya following the fall of Moammar Gadhafi.

She said there was "no doubt" such weapons were also used in an attack by militants on an Algerian natural gas plant last week.

She noted the aftermath of the Arab spring has changed power dynamics and stretched security forces across the region thin.

Calling the campaign struggle against the Islamic fighters a necessary response to "a very serious, ongoing threat," Clinton said the "United States cannot permit northern Mali to become a safe-haven for Islamist rebels that could eventually pose a more direct threat to U.S. interests."

Noting the increased strength of al Qaeda in the Islamic Maghreb, the regional affiliate of the al Qaeda network fighting along side local Malians, Clinton warned that the United States must prepare for the possibility that groups like AQIM could threaten direct attacks on U.S. interests as they gain power.

"You can't say because they haven't done something they're not going to do it," Clinton said. "This is not only a terrorist syndicate, it is a criminal enterprise. So make no mistake about it, we've got to have a better strategy."

5. Republicans still aren't buying it

While their tone was generally respectful, several Republican senators made clear they were unsatisfied with Clinton's answers.

Sen. John McCain, R-Arizona, one of the administration's toughest critics since the Benghazi attack, took Clinton to task for what he considered lackluster attention to the growing threat in Benghazi.

McCain wanted to know why Clinton hadn't read a cable from Ambassador Christopher Stevens warning that the mission in Benghazi could not survive a sustained assault.

Sen. Rand Paul said it would have been an offense worthy of firing Clinton had he been president.

McCain also blasted Clinton's answers to questions about the administration's claim that a protest had taken place in Benghazi.

"The American people deserve to know answers, and they certainly don't deserve false answers," McCain told Clinton.

Clinton was more diplomatic with her old friend, saying she respected his strong feelings for the incident given his own relationship with Stevens, but that they disagreed about what happened and when it happened with respect to explaining events.

In addition to lessons the State Department learned about improving security at diplomatic posts, Clinton, who called the Benghazi attack an act of terrorism since Day One, suggested the administration might learn another lesson.

"Just withhold. Don't say what you don't know for sure until it's finally decided."