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Nearly six weeks later, the attack on the U.S. mission in Benghazi, Libya, that left Ambassador Chris Stevens and three other Americans dead is still shrouded in mystery. A clearer outline of the attack, though, is emerging.

A credible witness tells Fox News that, prior to the attack, he heard a mob approaching the mission’s front gate, chanting blood-thirsty slogans, before they broke in. He said it was less like a demonstration and more like a warm-up to battle.

This could explain how others thought, including some I spoke with, that the attack started as a protest.

In the crowd, we are told, were members of Islamist groups from Benghazi. They all deny responsibility for the attack.

One such figure, singled out in the past week, was one-time Brigade leader Ahmed Abu Khattalah. Both The New York Times and The Wall Street Journal last Wednesday, citing Libyan officials, described him as a key suspect. They even suggested he was “on the run.”

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    I met with him openly last Friday. He admitted he was in the area of the mission the night of the attack (directing traffic) and inside the compound (assisting fellow brigade members). He denied any responsibility.

    Pointedly, though, he refused to express any remorse for the death of Stevens.

    The attack, Fox News is told by multiple witnesses, was strong, multi-pronged and organized. Those involved, said the attack involved various gauge weapons, including machine guns and RPGs.

    Aside from severe fire damage to nearly all the buildings, however, there was not a lot of evidence of a firefight. There was, at most, one RPG impact and half a dozen bullet holes at the main residence. There were few shell casings lying around.

    An explanation for this could be the closed-in nature of the mission’s neighborhood. There are houses, walls and trees all around. That could easily have amplified the impression of the attack.

    What was apparent: Defenses at the mission clearly proved ineffective at fending off those who decided to take on the mission.

    The compound was surrounded by walls 10 to 12 feet tall, topped by concertina razor and barbed wire. They were not breached. The lower metal front gate was undamaged. They didn’t have to be.

    It appears that the mob either scaled the gate and opened it from behind or simply pried open a side smaller door to gain access.

    As for the defensive positions, said to have been installed to serve as a  fallback for those warding off attackers, they were little more than two low walls of sandbags.

    There were several closed-circuit camera installations.While attackers targeted some, they appear to be intact and could already be supplying key video evidence regarding the start of the attack and the movement of the mob.

    The attackers were systematic. First storming and torching the Libyan militia barracks beside the main gate, then the main residence where Ambassador Stevens was located.

    They proceeded to the two other buildings on the compound, the second residence/dining facility, and the building used as the Tactical Operation Center, the brain room of the those protecting the American officials.

    It is clear security was on the minds of those at the compound. It has been reported that Ambassador Stevens was concerned about the growing terror threat in the region. And they were told about it as well.

    One Libyan official explained that he warned Americans in Benghazi just days before the attack about the risks. He said Americans acknowledged that.

    Long-range security planning was probably not on the minds of Stevens, information manager Sean Smith and others that night of Sept. 11. The “safe haven” area of the main residence, where they spent their last hours, is a horrid scene of desperation.

    It is this area, including bedrooms, bathrooms and closets, measuring about 90 square feet in size, sealed off with a locked gate from the rest of the building, where diplomatic special agents struggled to recover Stevens and Smith as the fire raged in other parts of the building.

    The body of Smith was found, but despite multiple entries, the ambassador had to be left behind, only to be found later by looters entering the building. He would then be taken to a Benghazi hospital where doctors failed to revive him.

    What happened exactly in those frenzied last minutes, and how Stevens wasn’t located, must certainly be another focus of investigators.

    Libyan officials admit to us that they are not close to finding or arresting any key suspects. And there has been no word on that either from Washington.

    What Fox News did hear though, throughout the visit, was the unmistakable hum of surveillance aircraft circling over Benghazi. Some folks most assuredly are listening, watching, waiting and trying to make sense of the still muddled scene down below.