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Case closed: FBI says researcher was anthrax killer

WASHINGTON -- The FBI sought to close the book on its long, frustrating hunt for the killer behind the 2001 anthrax letters Friday, formally ending its investigation and concluding a mentally unhinged scientist was responsible for killing five people and unnerving Americans nationwide.

After years of false leads, no arrests and public criticism, the FBI and Justice Department said Dr. Bruce Ivins, a government researcher, acted alone.

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.

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.

Many details of the case have already been disclosed, but newly released FBI documents paint a fuller portrait of Ivins as a troubled doctor 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, terror attacks. Postal facilities, U.S. Capitol buildings and private offices were shut down 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.