Four Americans, including U.S. Ambassador to Libya Chris Stevens, were killed Tuesday as gunmen set fire to and fought security forces at the U.S. Consulate in Benghazi, Libya.

The attack came as protesters outside the compound rallied against a movie that unflatteringly portrays Islam’s Prophet Mohammed. We are starting to get a clearer picture of what happened and why, but many more important and larger questions about the attack in Libya that still remained unanswered.

Who exactly is behind the attack and what was their motivation?

The attack - from people with guns and rocket-propelled grenades - came as people were protesting an anti-Islamic video outside the U.S. Consulate in Benghazi on Tuesday night, according to official Libyan and U.S. sources. However, it’s not clear whether the protesters were the ones who attacked.

U.S. sources are giving conflicting accounts about whether the attack was planned before the protest and whether the attackers used the protest as a diversion.

Sources tracking militant Islamist groups in eastern Libya say that a pro-al Qaeda group responsible for a previous armed assault on the consulate – called the Imprisoned Omar Abdul Rahman Brigades - is a chief suspect in the attack.

The sources also note that the attack immediately followed a call from al Qaeda leader Ayman al-Zawahiri for revenge for the June death of Abu Yahya al-Libi, a senior Libyan member of the terror group.

Noman Benotman,  president of the counter-extremist group Quilliam Foundation in London, told CNN, "An attack like this would likely have required preparation. This would not seem to be merely a protest which escalated."

"According to our sources, the attack was the work of roughly 20 militants, prepared for a military assault; it is rare that an RPG7 is present at a peaceful protest," Benotman said.

Ex-SEALs, online gaming maven among Benghazi dead

That analysis is supported by some U.S. sources who say the attack on the consulate is believed to have been planned. The sources say the attackers used the protest as a diversion to launch the attack, although the sources could not say if the attackers instigated the protest or merely took advantage of it.

However, one U.S. official told CNN on Thursday that intelligence information indicated that the attack wasn’t premeditated.

Additionally, Tommy Vietor, a National Security Council spokesman, told CNN Wednesday night that “there is a lot of press speculation for who did this and why, but at this stage it would be premature to ascribe any motive to this reprehensible act.”

U.S. intelligence officials believe that it is very unlikely that the core of al Qaeda was behind the attack, one such official said Thursday. The official did not rule out a group sympathizing with al Qaeda.

The top Republican on the House Intelligence Committee said Thursday that the strike "has all the hallmarks of an al Qaeda operation or an al Qaeda affiliate."

"One of the things that we've noticed over the last six or seven months is that al Qaeda in the Maghreb, northern Africa, have said they're really eager to strike northeastern targets. We've seen cells in Libya and Egypt starting to develop," U.S. Rep. Mike Rogers, R-Michigan, told CNN's "Starting Point."

Libyan Deputy Interior Minister Wanis al-Sharif said Wednesday that a group of heavily armed militants "infiltrated the march to start chaos.” Libya’s government blamed remnants of the Gadhafi regime, which was overthrown last year.

There was some speculation Wednesday about whether the 11th anniversary of the September 11, 2001, terrorist attacks had anything to do with the Benghazi assault. Secretary of State Hillary Clinton said the timing was unsettling for Americans, but it provided a reminder that "our work is not yet finished."

U.S. Sen. Dan Coats, a Republican from Indiana who is a former ambassador to Germany, said he thought the timing couldn't be ignored.

"I think its no coincidence that this happened on September 11," he said.

Was the attack planned and were proper security measures in place?

Wednesday night, U.S. officials told CNN's Suzanne Kelly that there were no actionable intelligence that this attack was being planned. But there appear to be some conflicting reports on the matter. Earlier Wednesday, sources said they believed the attack was planned, and that the protest of an obscure film that mocks Muslim faith was used as a diversion.

State Department Under Secretary Patrick Kennedy, during a briefing to Capitol Hill staff, offered his opinion that the attack was planned because of the extensive nature of the attack and the "proliferation" of small and medium weapons.

Could any of this been prevented?  And what kind of security was in place at the consulate? Given that it was September 11, and there has been unrest in the area, were any measures taken to step up security at U.S. posts around the world? And if not, should there have been?

Rep. Mike Rogers, chairman of the House Intelligence Committee, told CNN's Wolf Blitzer on Wednesday night that he and other officials had never been told of chatter or any indication that something like this was about to happen at the U.S. consulate in Benghazi.

"We didn't get the warning you would hope to get in an event like this, so we could have prevented the loss of life, and you know, with a horrible tragedy for losing a U.S. ambassador, Mr. Stevens," he said. "We think that we'll be able to go back and take a look. Again, we're going to rescrub all of that."

Rogers said that intelligence officials will check to see whether they missed any signs that the attack was coming.

"But I don't believe so," he said. "I don't believe there was some smoking gun that was missed leading up to this. And there wasn't that kind of chatter that would lead you to believe that this event was happening on this day with this specific target. I didn't see anything like that. I don't think our intelligence services have. But we're going back to make that scrub to make sure we understand fully what the picture was leading up to the event and subsequent to the event."

State Department spokeswoman Victoria Nuland told reporters Thursday that security at the Benghazi consulate in advance of the September 11 anniversary was "appropriate for what we knew." She cited a local guard force stationed around the outer perimeters and a "robust" American security presence in the compound.

What is the role of the film in all of this?

Tuesday's protest outside the consulate in Benghazi, as well as a protest 700 miles away at the U.S. Embassy in Cairo, Egypt, seemingly began because of outrage over a YouTube clip of a film that portrays the Prophet Mohammed as a womanizer, buffoon, ruthless killer and child molester.

Islam forbids all depictions of Mohammed, let alone insulting ones.

There are still many questions swirling about the video.

An actress in the video, who asked not to be identified, told CNN she and the other actors had no idea that they were performing in a movie about Mohammed. Lines about Mohammed and Islam were dubbed in after the movie was shot, she said.

The actors who'd responded to a July 2011 casting call thought they were making an adventure film set 2,000 years ago called "Desert Warrior." That's how Backstage magazine and other acting publications described it.

The 80 cast and crew members released a statement saying said they were "grossly misled" about the film's intent.

"The entire cast and crew are extremely upset and feel taken advantage of by the producer," they said in a statement.

They said they were "shocked by the drastic rewrites of the script and lies that were told to all involved," and "we are deeply saddened by the tragedies that have occurred."

The actress said that the character of Mohammed in the movie was named George when it was shot, and that after production wrapped she returned and read other lines that may have been dubbed into the piece.

What happens next?

Since Tuesday's deadly assault in Libya - and a protest the same day at the U.S. Embassy in Cairo - demonstrations, both small and large, have been reported in Israel, Gaza, Libya, Egypt, Yemen, Sudan, Tunisia, Morocco, Iraq, Iran and among Muslims in the Indian-controlled region of Kashmir. Security has been heightened at U.S. diplomatic missions worldwide.

While some protesters say they have not seen any of the online film, they were incensed by reports of its depiction of the Prophet Mohammed.

Which leads to one of the big questions moving forward: Will the outrage continue to grow?

Regardless of whether the attack on Libya has anything to do with the film, people angry about the movie have flocked to many U.S. embassies. And with Muslims' Friday prayers tomorrow, there was some question about whether there could be an escalation of violence.

"I don't know if it's a likelihood, I'd say it's a possibility," U.S. Ambassador to Afghanistan James Cunningham said in Kabul. "I hope the message out of the mosques will be one of restraint; I know there will be many messages like that because we've been through this. In other places the messages will be more extreme, we hope those places will be as isolated as possible and that people will realize this is the work of a very, very small group of people who are able to use modern tech to spread what they do more widely, but it doesn't represent anything really except disrespect. And overreacting to it is, in a way, rewarding this or responding to this disrespect."

The other big question is exactly how the United States will respond to the attack and what impact a response could have in diplomatic terms in some countries currently reeling from unrest.

We know the United States is deploying warships and surveillance drones in its hunt for the killers of the four U.S. diplomatic staffers, and a contingent of 50 Marines has arrived to boost the security of Americans in the country.

The drones are expected to gather intelligence that will be turned over to Libyan officials for strikes, a U.S. official said. Two American destroyers also are en route to the Libyan coast, U.S. officials told CNN. Both the USS Laboon and USS McFaul are equipped with satellite-guided Tomahawk cruise missiles that can be programmed to hit specific targets.

The move "will give the administration flexibility" in case it opts to take action against targets inside Libya, one senior official said. As of late Wednesday, the McFaul was making a port call on the Mediterranean island of Crete, while the Laboon was outside Gibraltar, a few days from Libya.

It seems clear that whatever action is taken, strong rhetoric from U.S. officials indicate they will do whatever possible to find those responsible for the attack.

"We will not waver in our commitment to see that justice is done for this terrible act," U.S. President Barack Obama said Wednesday. "And make no mistake, justice will be done."