Greg Cochran says, in defense of the much maligned FBI, that in 2001 the technology didn't really exist to sequence the anthrax found in mailed envelopes in the fall of that year. As you'll recall, the Human Genome Project had spent years sequencing Craig Venter's DNA, not finishing until about then.
By the middle of the decade, however, genome sequencing technology had improved so much that the FBI could hire biotech firms to sequence the evidence, which traced the terrorist anthrax to a particular batch accessible only to about ten people at Ft. Detrick. (That's assuming that the initial inspection of the evidence at Ft. Detrick in 2001 didn't contaminate the sample -- which may or may not be a Big If.)
What we don't know yet is how solid the links are to Ivins as the One of the Ten. He sounds like he was always pretty eccentric, and was fairly crazy at the end. Still, one concern would be: what if the FBI picked out the most eccentric of the ten for surveillance, and that, rather than guilt, drove him around the bend? Anyway, we should know more pretty soon.
It might not be a bad idea to buy out the other nine people at the lab who had access to the terror anthrax and pay them all to take early retirement.