Compared to what we've seen, I'm still expecting to find out a 15-year-old kid with a chemistry set did it.
The folks that are running around yelping that we gave anthrax spores (well, usually they are even more vague for obvious reasons, they say "bioterror agents," or some such nonsense) to the Iraqis have no understanding that anthrax is a naturally-occurring agent. It's weaponizing it that is difficult, i.e., grinding it into a such fine powder that it can remain suspended in air, etc.
Since 9/11 everything rates that designation. At least now we finally know who was behind the Tylenol murders of two decades ago: Muslim terrorists.
"That's not what I'm getting from all the reports."
Then I urge you to read...
FBI's Theory on Anthrax Is Doubted, from today's Washington Post.
This is the best-researched, most complete article on anthrax yet done by the mainstream media. It effectively addresses your questions.