Many people there have easy access to them since they are not secured after the uprising and a regular person can instantaneously turn from postesor to launching an RPG!
Also, these are some things I've read in USA today, other news papers and seen online that make me say it was beyond our control to a large extent (the attack). Maybe in hindsight we should have withdrawn our personne but at the same time, maybe those who were there wanted to stay and perhaps we didn't have enough info to think there would be direct attacks on the embassy.
The Libyan government reminded us that it was a military assault, and that antagonistic militia and Al Qaeda affiliates might be better armed than the Libyan military, and that the entire official Libyan Army consists of only about 6,000 men. The rest of the armed forces in Libya are militia with conflicting local allegiances that might at any time over ride the allegiance to the (more or less official) Libyan government, which acknowledges itself as provisional and subject to quick change after elections.
The Libyan government suggested that if we wanted the site to be secure, it would be up to the US military. But they also warned us that it might make for a public relations problem, for reasons with which the US government agreed.
Because mortars and heavy weapons were used in the attack, and because we could not rely on local authorities, we would have to:
(1)Use a disproportionately large number of troops
(2)Use armour and heavy weapons
(3)Seize a large territory of currently populated area
Here
From NPR:
Violence Takes Root In Post-Gadhafi Security Vacuum
Published: September 17, 2012
by Leila Fadel
The deadly attack on the U.S. Consulate in Benghazi, Libya, that killed Ambassador Chris Stevens and three other American personnel has highlighted the serious post-Moammar Gadhafi security vacuum in the country.
The problem is much bigger than a few rogue militants: Eastern Libya is awash with heavy weaponry; security forces are weak; assassinations are plaguing Benghazi; and the people with the biggest guns rule.
Raouf Mohammed knows all of this from personal experience, and he wears a silver ring as a reminder: It belonged to his father, Mohammed Hadiya, who was wearing it the day he was shot down outside a mosque.
LINK
http://m.npr.org/story/161303849