"The killings of the US ambassador to Libya and three of his staff were likely to have been the result of a serious and continuing security breach..."

Says The Independent.

Senior officials are increasingly convinced... that the attack was in revenge for the killing in a drone strike in Pakistan of Mohammed Hassan Qaed, an al-Qa'ida operative who was, as his nom-de-guerre Abu Yahya al-Libi suggests, from Libya, and timed for the anniversary of the 11 September attacks....

According to security sources the consulate had been given a "health check" in preparation for any violence connected to the 9/11 anniversary. In the event, the perimeter was breached within 15 minutes of an angry crowd starting to attack it at around 10pm on Tuesday night. There was, according to witnesses, little defence put up by the 30 or more local guards meant to protect the staff. Ali Fetori, a 59-year-old accountant who lives near by, said: "The security people just all ran away and the people in charge were the young men with guns and bombs."

Wissam Buhmeid, the commander of the Tripoli government-sanctioned Libya's Shield Brigade, effectively a police force for Benghazi, maintained that it was anger over the Mohamed video which made the guards abandon their post. "There were definitely people from the security forces who let the attack happen because they were themselves offended by the film; they would absolutely put their loyalty to the Prophet over the consulate. The deaths are all nothing compared to insulting the Prophet."

In this analysis, the video was used to manipulate the mob and the security forces, but the drone attack was the motivation for the killings.