WASHINGTON (AP) -- Wrapping up one of its most vexing investigations, the FBI concluded that Army scientist Bruce Ivins acted alone in the 2001 anthrax mailings that killed five people and further unnerved a nation still reeling from the 9/11 attacks.
The agency formally closed the case Friday, ending the long, frustrating hunt for the killer after years of false leads, no arrests and public criticism.
Ivins killed himself in 2008 as prosecutors prepared to indict him for the attacks. He had denied involvement, and his family and some friends have continued to insist he was innocent.
Many details of the case have already been disclosed, but newly released FBI documents paint a fuller portrait of Ivins as a troubled researcher whose life's work was teetering toward failure at the time the letters laced with anthrax were sent. As the U.S. responded to the mailings, that work was given new importance by the government, and he was even honored for his efforts on anthrax.
The documents also describe what investigators say was Ivins' bizarre, decades-long obsession with a sorority. The anthrax letters were dropped in a mailbox near the sorority's office in Princeton, N.J.
The letters were sent to lawmakers and news organizations as the nation reeled in the aftermath of the Sept. 11, 2001, terrorist attacks. Postal facilities, U.S. Capitol buildings and private offices were shut for inspection and cleaning by workers in hazardous materials "space suits" from Florida to Washington to New York and beyond.
In closing the case, officials also released reams of evidence and a 92-page summary of their findings.
To the FBI's critics, the mountain of new documents could not paper over what they say are glaring holes in the case.
"The evidence the FBI produced would not, I think, stand up in court," said Rep. Rush Holt, a Democrat whose New Jersey district includes the Princeton mailbox used in the attacks. "But because their prime suspect is dead and they're not going to court, they seem satisfied with barely a circumstantial case."
Ivins' lawyer, Paul Kemp, said he saw nothing new in the findings. "All they have confirmed is that they suspected him belatedly after finding out he had psychological problems," he said. "Sadly, they substitute that for proof."
Authorities say Ivins' death capped a yearslong cat-and-mouse game with investigators, in which he repeatedly offered to help the FBI catch the killer, cast suspicion on his colleagues and tried numerous forms of subterfuge.
He passed a polygraph in connection with the probe in 2002, but investigators learned years later that he had been prescribed psychotropic medications at the time, and examiners who reassessed the results concluded he exhibited classic signs of the use of countermeasures to pass the test.
Authorities say Ivins nursed a secret fascination with the sorority Kappa Kappa Gamma that dated back decades, and at one point years ago, they say, he stalked a member of the sorority.
The new documents also present a novel theory why the anthrax notes featured block writing that highlighted specific letters within words.
Investigators believe Ivins' use of the letters was part of a secret code that had two possible meanings: pointing to a colleague or stating a specific dislike of New York. Two of the letters were sent to New York - one to the New York Post, another to NBC's then-anchor Tom Brokaw.
Investigators had tried earlier to build a case against biowarfare expert Steven Hatfill, who had worked for a time in the same military lab as Ivins, but ultimately turned away from that theory and had to pay him a multimillion-dollar settlement.
The anthrax spores killed five people: two postal workers in Washington, D.C., a New York City hospital worker, a Florida photo editor and a 94-year-old Connecticut woman who had no known contact with any of the poisoned letters. Seventeen other people were sickened.
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