Spencer Ackerman provides a good first summation of an extended, coordinated attack that killed the US Ambassador to Libya at the Danger Room blog.
It was not a simple mob that attacked the U.S. consulate in Benghazi on Tuesday, killing four Americans. Benghazi was the scene of a pitched battle, one in which unknown Libyan assailants besieged American diplomats with small-arms fire for over four hours, repelling several attempts by U.S. personnel to regain control of it.
Nor was what happened in Benghazi a simple story of Americans assaulted by the Libyans they helped to liberate from Moammar Gadhafi last year, American officials say. Libyan security forces and a sympathetic local militia helped the Americans to suppress the attack and get the diplomats inside to safety.