A month later, Ivins, who had been under constant surveillance by the FBI, was dead.
Ft. Detrick was the focus early on in the investigation because it is one of only a few labs known to work with the strain of anthrax used in the attacks.
Investigators narrowed their search further when they produced evidence that envelopes used in the attack were purchased at a post office near Ft. Detrick.
One theory the FBI has been pursuing is whether Ivins might have mailed the anthrax to further his research on anthrax vaccines. His research included classification of anthrax spores and tracking the success of anthrax vaccines administered to animals.
Duley said she feared for her life.
"I'm scared to death," she said on the courtroom audio recording.
And she made this chilling claim: "He has been forensically diagnosed by several top psychiatrists as a sociopath, homicidal killer," she said.
Ivins' lawyer said Friday that his client was innocent, and that he fully cooperated with the government's investigation.
The Justice Department remained tight-lipped on the investigation, releasing a statement Friday saying there have been "significant developments," but declining to elaborate. Next week, the FBI is expected to release its evidence, which is currently under court seal.
ABC News' Z. Byron Wolf contributed to this report.