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Members of a militant group called Ansar al-Sharia, which translates to Supporters of Islamic Law, may have been involved in organizing the attack on the U.S. Consulate, officials said. It is also possible that member's of al-Qaida could have been involved.

"This was a coordinated attack, more of a commando-style event," House Intelligence Committee Chairman Mike Rogers, R-Mich., told CBS News. "It had both coordinated fire - direct fire and indirect fire. There appeared to be military maneuvers approaching the facility."

It was previously believed that the attack was spurred by a spontaneous mob, upset by an online video ridiculing the Prophet Mohammed. 

While the exact cause of the deaths has yet to be determined, officials told CNN Wednesday that the diplomats died of smoke inhalation while trying to escape to the roof of the burning building, after it was struck by a rocket-propelled grenade.

From CBS:

Wanis al-Sharef, a Libyan Interior Ministry official in Benghazi, said there had been threats that Islamic militants might try to take revenge for the death of al Qaeda's No. 2 commander Abu Yahya al-Libi...

Some authorities are looking at the possibility that the attack may have been planned to coincide with the anniversary of the Sept. 11 terror attacks and this week's killing in Yemen of Saeed al-Shihri, who was second in command of al Qaeda in the Arabian Peninsula.

Stevens is the first U.S. ambassador to be killed on duty since 1979.

Read more of Neon Tommy's coverage on Libya here.

Reach Senior News Editor Sarah Parvini here; follow her on Twitter.