The Guardian writes about the FBI:
The Bureau is a fitting faith-based institution for the times. It has a definite and distinctive modus operandi: to decide upon unlikely suspects and then to pursue them with an unshakeable conviction of guilt regardless of the failure to win conviction. In a sadistic form of barratry, the Bureau treats each failure to secure a conviction as an opportunity to raise new and ancillary charges and all the time leaks to reporters in a way that would in most common law jurisdictions have the judge throwing the case out.
Plus more info from CargoCult with fun scientific spore details.
The only likely suspects are the ones the FBI has avoided: Dugway Utah and Battelle Memorial in West Jefferson Ohio. They had the means (they'd made the stuff before) and the motive (massive Project Bioshield contracts and expansion of the U.S. biowarfare complex).
Wall Street Journal Editorial says Ivins wasn't the Anthrax killer; and that the weaponized anthrax couldn't have been created in Ivins' lab.