A few things to take note of here. First, this is more evidence that the administration knew, or should have known, that this attack had nothing to do with a protest over a video. Second, this seems a massive intelligence failure. Not only was their ample evidence and warning of the very real danger, but there seems to be ample evidence that the administration knew, or should have known, that the first line of defense (that being the Libyan guards) may actually have been the first line of attack against the ambassador.
"More than six weeks after the shocking assault on the U.S. consulate in Benghazi -- and nearly a month after an FBI team arrived to collect evidence about the attack - the battle-scarred, fire-damaged compound where Ambassador Chris Stevens and another Foreign Service officer lost their lives on Sept. 11 still holds sensitive documents and other relics of that traumatic final day, including drafts of two letters worrying that the compound was under "troubling" surveillance and complaining that the Libyan government failed to fulfill requests for additional security.
... The two unsigned draft letters are both dated Sept. 11 and express strong fears about the security situation at the compound on what would turn out to be a tragic day. They also indicate that Stevens and his team had officially requested additional security at the Benghazi compound for his visit -- and that they apparently did not feel it was being provided.
One letter, written on Sept. 11 and addressed to Mohamed Obeidi, the head of the Libyan Ministry of Foreign Affairs' office in Benghazi, reads:
"Finally, early this morning at 0643, September 11, 2012, one of our diligent guards made a troubling report. Near our main gate, a member of the police force was seen in the upper level of a building across from our compound. It is reported that this person was photographing the inside of the U.S. special mission and furthermore that this person was part of the police unit sent to protect the mission. The police car stationed where this event occurred was number 322."
The account accords with a message written by Smith, the IT officer who was killed in the assault, on a gaming forum on Sept. 11. "Assuming we don't die tonight. We saw one of our ‘police' that guard the compound taking pictures," he wrote hours before the assault."