(Dawn Megli / Neon Tommy)

Sixteen days after the U.S. ambassador to Libya was killed in a terrorist attack on the U.S. embassy, fears of a near-total security lapse have kept FBI agents from visiting the site, according to The New York Times.

The investigators are trying to understand the scene from more than 400 miles away, in Tripoli.

Investigators have been so careful that they haven't brought potential Libyan witnesses to the scene of the assassination, either.

They have been interviewing witnesses in cars outside the embassy, according to The New York Times, and the embassy was further evacuated on Thursday with a heightened security alert.

"It's a cavalcade of obstacles right now," said a senior American law enforcement official who is receiving regular updates on the Benghazi situation, according to The New York Times.

The embassy is apparently badly degraded, looted and burned, and it's very difficult to "see what evidence can be attributed to the bad guys," the source said.

(Read Neon Tommy's international blog Diplomatic Immunity here.)

The embassy attack has been officially characterized as a terrorist attack, orchestrated and executed by the North African unit of Al Qaeda, according to the Washington Post.

U.S. intelligence officials claimed that their idea about the attack has grown stronger in the past week, and believe that it was carried out by two or three fighters linked to Al Qaeda in the Islamic Maghreb.

"There are people who at least have some association with AQIM," said another senior U.S. intelligence official, who added that "it's not so direct that you would say AQIM as an organization planned and carried this out."

According to the Post, it is believed that the militants had been preparing the Benghazi embassy assault for weeks but were so disorganized that, after the battle started, they had to send fighters to retrieve heavier weapons.

Therefore, they think that the attack was not necessarily timed to align with the anniversary of the Sept. 11 attacks on the World Trade Center.

(Read all of Neon Tommy's Middle East coverage here.)

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