According to senior diplomatic sources, the US State Department had credible information 48 hours before mobs charged the consulate in Benghazi, and the embassy in Cairo, that American missions may be targeted, but no warnings were given for diplomats to go on high alert and "lockdown", under which movement is severely restricted.

Mr Stevens had been on a visit to Germany, Austria and Sweden and had just returned to Libya when the Benghazi trip took place with the US embassy's security staff deciding that the trip could be undertaken safely......

.......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."

Mr Stevens, it is believed, was left in the building by the rest of the staff after they failed to find him in dense smoke caused by a blaze which had engulfed the building. He was discovered lying unconscious by local people and taken to a hospital, the Benghazi Medical Centre, where, according to a doctor, Ziad Abu Ziad, he died from smoke inhalation.