My guess, those Montana Militia guys,
Amish militants,
DAR radicals.
My guess, it's Iraqi made, since it's not resistant to antibiotics. Both the U.S. and Soviet Union were supposed to have been capable of producing genetically engineered, antibiotic resistant strains.
But Iraq is supposed to lack that genetic engineering technology.
First it was, then it wasn't, now it is again. I think our government is purposefully muddying up the waters about the anthrax source so as to confuse our enemies, and vicariously--to confuse us.