We now know that the FBI learned in early 2005 from state-of-the-art gene sequencing that terrorist anthrax had to come from one of ten people at Ft. Detrick, and that Stephen Hatfill, the "person of interest" in this case, wasn't one of them.
How long did it take the FBI investigators to refocus themselves?
David Willman's breakthrough article in the 8/1/08 LA Times tells us:
Federal investigators moved away from Hatfill -- for years the only publicly identified "person of interest" -- and ultimately concluded that Ivins was the culprit after FBI Director Robert S. Mueller III changed leadership of the investigation in late 2006.
The FBI's new top investigators -- Vincent B. Lisi and Edward W. Montooth -- instructed agents to reexamine leads or potential suspects that may have received insufficient attention. Moreover, significant progress was made in analyzing genetic properties of the anthrax powder recovered from letters addressed to two senators.
The renewed efforts led the FBI back to USAMRIID, where agents first questioned scientists in December 2001, a few weeks after the fatal mailings.
By spring of this year, FBI agents were still contacting Ivins' present and former colleagues. At USAMRIID and elsewhere, scientists acquainted with Ivins were asked to sign confidentiality agreements in order to prevent leaks of new investigative details.
So, it looks like about a year and a half went by while the old FBI team continued to spin its wheels, stuck in the rut of blaming Hatfield. People don't like to admit they're wrong.
It was only in late 2006 when the FBI boss reassigned the old investigators and brought in a new team that the FBI began to make progress in finding a suspect that fit the genome sequencing data that they had had since early 2005. That year and a half lag may help explain why the government paid so much ($5.8 million) to Hatfill recently.
Clearly, much of the blame directed at Hatfield was because, like the bad guy in a Hollywood thriller, he had lived for a number of years in Rhodesia and South Africa. But there was some other circumstantial evidence -- he had a history of claiming advanced degrees he hadn't earned, he had been very interested in anthrax terrorism, he was taking Cipro at the time of the attacks for sinus surgery, and some minor coincidences. He was not a totally unreasonable suspect at first.