One of the (many) reasons I've been skeptical of of the charges that Able Danger ID'd Atta in '99 is that--according to LAT reporter Terry McDermott, who wrote the definitive take on the 9/11 hijackers--Atta wasn't even recruited by AQ until 2000. And he didn't enter the U.S. until then either. Nor did he seem to have a presence on the public databases, such as Nexis, that Big Source Shaffer says Able Danger relied on.
Could it have been a case of mistaken identity? That is, Atta wasn't flagged pre-9/11 but it just so happens that guys with similar names were. Tom at JustOneMinute raises that posssibility, naming a former Palestinian terrorist named Mahmoud Atta.
And here's another one: Back in the late 1990s there was a Egpytian-born man who was linked in sting-operation trying to ships arms to militants to Egypt. That man's name is Mohamed el Amir. Mohamed Atta's full name is Mohamed el-Amir Awad el-Sayed Atta. Or as he was commonly known: Mohamed el Amir.
(Thanks to Terry and another big paper reporter for the Atta doppleganger theory.)
UPDATE:
I thought I had posted this yesterday--turns out, I forgot the whole "publish" button concept. In any case, Mickey has since gone into detail explaining why the two Atta theory makes so much sense.
I concur. In fact, the two-Atta theory only leaves one major issue unexplained: What about the three other 9/11 hijackers that Able Danger purportedly fingered? Possible answers: 1) Mr. Shaffer was embellishing. (Has he named the specific hijackers who were purportedly ID'd?) 2) They indeed were named and--just like Atta may be--are also cases of mistaken identity. That would be understandable. It's easy for Arabic speakers to mix up Arabic names. Indeed, the FBI itself originally pegged four or five wrong people as the 9/11 hijackers.