I've heard so many conflicting reports, including the Iowa one, that I don't know what to beleive anymore. Given our lax immigration laws and PC sensibilities, I think it would be easy for a couple of swarthy males to make with some Anthrax out of Iowa. Just as a few "Asian-Americans" could slip our nuke secrets out of LosAlamos.
From this post:
"Scientists investigating the attacks say the bacteria used is similar to the 'Ames strain' of anthrax originally cultivated at Iowa State University in the 1950s and later given to labs throughout the world, including Iraq."