From what I understand about the event in Libya, the consulate was housed in a temporary location...not secured in the usual manner. I saw a reference earlier that two of the dead were Marines who died in defense of the sovereign territoty of the US.
Check this out...
Security at the consulate was apparently provided by Libyan nationals hired by the United States. While security for American embassies is typically provided by our own Marines, the two Marines reported killed in yesterday's attacks appear not to have been stationed at the embassy, but were sent there from another unknown location as the violence erupted. There is also no indication if these two Marines were the only American military personnel on site at the time of Ambassador Stevens's death.
http://www.breitbart.com/Big-Government/2012/09/12/Where-Were-the-Marines
The Ambassador was apparently betrayed by his hired security detail:
...Stevens, 52, and other officials were moved to a second building - deemed safer - after the initial wave of protests at the consulate compound. According to al-Sharef, members of the Libyan security team seem to have indicated to the protesters the building to which the American officials had been relocated, and that building then came under attack.
http://www.cbsnews.com/8301-202_162-57511043/assault-on-u.s-consulate-in-benghazi-leaves-4-dead-including-u.s-ambassador-j-christopher-stevens/?tag=stack
The attacks in Egypt and Libya were quite obviously well planned and coordinated...timed for the anniversary of the WTC's destruction.

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http://hotair.com/archives/2012/09/12/cbs-libyan-security-team-fingered-us-ambassador-to-be-killed/