(CBS News) NEW YORK - Secretary of Defense Leon Panetta said Thursday that a group of terroristson the U.S. Consulate in Benghazi, Libya, but that the identity of their group or affiliation is unknown.
That description differs from the administration's earliest comments about the Sept. 11 assault that killed the U.S. Ambassador to Libya and three other Americans, which described the attack as a spontaneous outgrowth of protests against an anti-Islam film produced in the U.S.
While several militant groups have been mentioned as possible culprits, including Ansar al Sharia, senior correspondent John Miller said that discerning the specific identity of those responsible is difficult.
"We want a wiring diagram, we want an organized picture: 'It was al Qaeda who ordered it, it was Ansar al-Sharia who carried it out, it was this group that assisted,'" Miller said. "The problem is, the lines have blurred between those groups and their members. Ansar al-Sharias are popping up in places like Benghazi, but also in Yemen, also in Tunisia, in all these countries. And they're not al Qaeda, but they are reading from the al Qaeda narrative and they are being influenced by people who are formerly influential extremists in al Qaeda.
"The actual truth is, the picture isn't that clear, but we can piece it together, and that's not satisfying to people who are used to saying, 'You can attach this attack to that group.'
"One of the reasons you are seeing all of the groups who are reading from the al Qaeda narrative no longer calling themselves al Qaeda is because they realize that makes them radioactive for things like fund-raising."
"So in your briefings every day you're informed a little bit more what you learned the day before, a lot like what we do," Miller said. "Once the news cycle collides with the intelligence cycle, collides with the political cycle, the last thing that's standing is information.
"And this is what drives intelligence professionals crazy, because they say, 'We're working very hard on getting this right, and people are spinning it every day.'"
The U.S. State Department also announced on Thursday that it is pulling more staffers out of the American Embassy in Tripoli, Libya, for security reasons. But FBI investigators have not yet been allowed into the crime scenes at the consulate and safe house in Benghazi, Miller said.
"The security situation on the ground there is so brittle that the Libyan government is very reluctant to have a team of a couple of dozen FBI people going into Benghazi, when the only people they could get to protect them are the militias, and right now they don't trust any of the militias," Miller said.
"The key militia that's in charge of protecting the hospital where the wounded were taken from this attack is suspected of being behind the attack," Miller told Charlie Rose.
But time is less of an issue in this investigation, Miller added. "That crime scene was long ago compromised, trampled through, looted. It may or may not yield anything terribly important and if it does, it will yield it later."
To watch Miller explain the growing threat of Al Qaeda in the Islamic Maghreb and how intelligence officials are analyzing their link with the militant group Ansar al Sharia in Libya, click on the video player below.}