FBI Closes Anthrax-Letters Case After 10,000 Interviews

The FBI has closed its investigation into the case of the Army microbiologist believed to be responsible for mailing anthrax-laced letters that killed five people and injured dozens of others in 2001.

In announcing Friday that the investigation was over, the bureau released a report detailing the evidence against Dr. Bruce E. Ivins, a researcher at the Medical Research Institute of Infectious Diseases at Fort Detrick, Md., The New York Times reported.

Ivins killed himself in 2008, as federal prosecutors were preparing to charge him with using a weapon of mass destruction.

The FBI report, which accompanies 2,700 pages of notes and documents, reveals the scope of the investigation, which included more than 10,000 interviews on six continents. According to the Times:

The report also describes the F.B.I.'s theory that Dr. Ivins, who was fascinated by codes, embedded a complex coded message in the notes that he mailed with the anthrax. The coded message, based on D.N.A. biochemistry, alluded to two female colleagues with whom he was obsessed, the bureau said.

The report describes how a hidden F.B.I. surveillance agent watched in 2007 as Dr. Ivins threw out a book and an article that might reveal his interest in codes, then came out of his house at 1 a.m. in long underwear to make certain that the garbage truck had in fact taken his trash.

"I can hurt, kill, and terrorize," Dr. Ivins wrote in a 2008 e-mail message to a friend. "Go down low, low, low as you can go, then dig forever, and you'll find me, my psyche."

The letters laced with anthrax were mailed to media companies and to two U.S. senators the week following Sept. 11, 2001. Investigators said Ivins included radical Islamist rhetoric to make it appear that the letters were connected to the terrorist attacks.