1) Atta was passed weapons grade anthrax from Iraq during his one-day meeting in Prague.
2) Atta and his team were also given instruction as to how to create a primitive home laboratory so they could use the weapons-grade batch to grow additional batches. I would like any Freepers with biomedical background to confirm/deny whether this is possible and if so, how difficult this might be.
3) This would explain
a) the mysterious one-day meeting,
(b) Atta's subsequent visits to pharmacists for treatmenty of a rash on his hands (caused by caustic agents used in the home lab?) and his associate's visit to a doctor for treatment of persistant bad cold symptoms
4) This would explain the presence of 2 grades of anthrax seen in the aftermath:
(a) a primitve, non-centrifuged grade (The American Media anthrax and other instances) and
(b)one instance of the pure grade (Daschle's office and perhaps others).
5) Atta, once committed to his suicide flight, had no need to save the pure batch -- or else they saved the pure batch for the Senate and perhaps the White House.
6) Atta could have directed associates, still at large, to mail the anthrax one week after the Twin Towers crash.
7) The American Media batch may have been sent before the crash, as a test run. Since Atta lived nearby, perhaps he was observing (perhaps through an associate) to see whether any employees reported sick -- thereby confirming that the strategy would work. This would explain the choice of a near-by target for the trial run.
8) The crop-duster episodes, and Atta's interest in them, was perhaps an alternative strategy if the mail-strategy was a bust.
I suspect others have drawn similar conclusions -- please share.
Pretty tough without a PhD level lab and some unsuspecting or fanatical biology folk to process this stuff; it's much easier to get the spores from producers abroad in the bulk amounts needed, possibly of varying quality. I like the rest of your theory though.
I also think this may argue the point that whoever did this had a very limited amount of anthrax in their possession.