Security was infiltrated by terrorists
http://www.thegatewaypundit.com/2012/10/leaked-documents-reveal-obama-administration-hired-al-qaeda-linked-radical-to-run-security-at-tripoli-embassy/?PageSpeed=noscript
Other articles:
http://www.weeklystandard.com/blogs/ansar-al-sharia-mans-security-benghazi_742320.html
Around 9:40 p.m., a few attackers scaled the wall of the diplomatic post and opened the front gate, allowing dozens of armed men in. Local Libyan security guards fled. - http://www.chron.com/news/politics/article/News-Guide-What-Benghazi-means-in-US-politics-5516982.php