BENGHAZI, Libya -- Witnesses in Benghazi, Libya, provide a chronology for the attack Sept. 11 on the U.S. consulate here that differs in significant ways from timelines released by U.S. officials in Washington, raising more questions about how the assault unfolded and the speed with which Americans at a nearby CIA annex responded to calls for help from the consulate.

The versions of the attack told here indicate that the last visitor who met with Ambassador Chris Stevens, who died in the assault on the consulate, departed at least 45 minutes earlier than U.S. officials in Washington have said. Witnesses here also suggest that the attack may have begun as many as 15 minutes earlier than officials in Washington have said.

Witnesses also said there was no indication that anyone in the U.S. diplomatic compound was aware before the assault that protests had broken out in neighboring Egypt over an inflammatory film about the Prophet Muhammad that was produced in the United States.

The differences in the timelines could mean that CIA officers stationed in a compound just 1.2 miles away may have waited as long as 40 minutes before setting out to assist the besieged consulate and might not have arrived there until more than an hour after the attack began. A timeline released by the CIA says help was dispatched after just 25 minutes and that it took the rescue squad 25 minutes to arrive.

At a minimum, the witness accounts suggest that after two months, the U.S. government still may not know the basic sequence of events and when key moments in the assault occurred.

What took place in Benghazi on the night of Sept. 11 and the early morning of Sept. 12 is the subject of at least three congressional hearings this week, beginning with a closed session of the Senate Foreign Affairs committee Tuesday and ending with separate sessions of the Senate and House of Representatives intelligence committees Thursday. Interest in those hearings, already high, only increased with the resignation Friday of retired Army Gen. David Petraeus, who resigned as the director of the CIA over an extramarital affair with his biographer, Army Reserve Lt. Col. Paula Broadwell.

What new information might be presented at those hearings isn’t clear. The hearings are closed to the public, and whatever details emerge most likely will come in the form of leaks from the participants.

But the timelines that have been offered by the State Department, the CIA and the Defense Department offer inconsistent versions of what took place during the deadliest assault on a U.S. diplomatic compound in more than three decades. And any account of what meetings or discussions, if any, took place at CIA headquarters in Langley, Va., as the events in Benghazi unfolded is still missing.

In addition to Stevens, a State Department computer expert, Sean Smith, died at the consulate. Two CIA security contractors, former Navy SEALs Tyrone Woods and Glen Doherty, died several hours later when assailants attacked the CIA annex, to which survivors of the assault on the consulate had fled.

According to witnesses, Stevens had arrived in Benghazi on Sept. 10 for a four-day visit, his first extensive stay in this city since he assumed the ambassador’s post in May.

On the evening of Sept. 11, Stevens met with the Turkish consul here, Ali Sait Akin, in what everyone agrees was his last official act. While State Department officials said Stevens escorted the Turkish consul out of the compound at 8:30 p.m., a guard at the compound and an official familiar with the meeting said Akin left at 7:45 p.m.