Our DoS and CIA assets in the middle east are only capable of going to embassy parties, or running western oriented "proprietary front" companies. But they can't walk 100 yards into the souk or market or back alleys without being spotted and put at great danger. We just don't have the kinds of spies who can go undercover in a group like the Osama Bin Laden (OBL) group. Nobody.
So yes, I would have to say that the fact that it was a large, expensive, coordinated, and suicidal attack with no fore warning tends to point at OBL, who is capable of sending a dozen or more suicide teams into the USA weeks in advance. The Palis couldn't do it without Mossad knowing. Only OBL or someone on that level we don't even know could do it.
God Bless America.
It could also be a nation state or states that specifically sponsored this action. I note that the only real candidates for this would be a state that could harness religous fervor in their supporters. I am not going to theorize any more at this point, but it could be a combination of entities.
Stay well - Yorktown