Investigators knew almost immediately that it wasn't part of any al Qaeda plot.
The first thing they did was track what killed Bob Stevens, and that was even before they knew there were any letters.
Stevens was killed by the Ames strain of anthrax, which is a RARE strain controlled and distributed by USAMRIID to just a few laboratories - 14 other labs in the U.S. and 3 outside of the U.S. (Canada, Sweden and England).
Then it became a matter of figuring out what lab it came from. They eventually proved that it originated at USAMRIID in Ft. Detrick, Maryland, and they even identified the specific flask it came from - flask RMR-1029 which was created and controlled by Bruce Ivins.
There's just no reasonable way that any al Qaeda member could have gotten his hands on that specific flask - particularly since there are many many other strains of anthrax around, including some that are more deadly than the Ames strain.
And, as I stated in another post, they even caught Ivins throwing away the code books for the "hidden message" in the media letters.
Anyone who still thinks al Qaeda did it just isn't looking at the facts. That was a dead idea nine years ago.
Who said anything about alqueda and anthrax??
And that strain was distributed all over the place....