Bruce Ivins, a biodefence scientist, apparently committed suicide as prosecutors prepared to indict him on charges related to the mailing of anthrax-laced letters in 2001. (Frederick News Post/Associated Press)

An American judge unsealed hundreds of pages of secret FBI documents on Wednesday, shedding light on the dead scientist accused of orchestrating a string of deadly anthrax attacks in the U.S.

The documents, including more than a dozen search warrants, outline the mountain of evidence the government collected against army microbiologist Bruce Ivins, 62, who committed suicide last week as prosecutors prepared to charge him with murder.

"Based on the totality of the evidence we had gathered against him, we are confident that Dr. Ivins was the only person responsible for these attacks," said Jeffrey Taylor, U.S. attorney for the District of Columbia.

He said the documents clearly show that Ivins, an anthrax researcher who worked at a biological warfare lab in Fort Detrick, Md., had grown, purified and dried the anthrax that was loaded into envelopes and mailed to U.S. Senate offices, news media headquarters and other locations across the United States.

Five people were killed after coming in contact with the packages in the fall of 2001, and 17 were sickened. The case emerged only weeks after the Sept. 11 attacks on New York City and Washington.

Ivins had sole access to anthrax spores

Investigators linked the anthrax used in the attacks to a specific type of spore that Ivins created and had sole access to, Taylor said. He said Ivins was only one of a handful of scientists capable of creating such pure and concentrated spores, and he was one of the few people with access to the machine needed to dry them.

Taylor said at the time of the attacks, Ivins was working an "inordinate" amount of hours alone at his lab at night and on weekends, something he normally never did. When investigators questioned him about it, he failed to provide a satisfactory explanation, Taylor said.

He said the envelopes the anthrax was mailed in was sold in the post office near Ivins' home in Frederick, Md., and that Ivins had a history of writing to U.S. politicians and news organizations. Ivins also had a history of travelling long distances to mail a letter, Taylor said, which could explain why the anthrax was mailed in a mailbox that is a seven-hour drive from Ivins' home.

The unsealed documents show that FBI agents searched Ivins' home, his cars and his safety deposit boxes. Investigators took more than 20 swab samples and seized dozens of items, including family photos, video cassettes, written information about guns and a copy of the novel The Plague by Albert Camus.

Also seized was an e-mail Ivins wrote days before the Sept. 11 attacks, warning that al-Qaeda leader Osama bin Laden had anthrax and was declaring war on the United States and Israel. Inspectors noted that the language in that e-mail and others is similar to the words used in the anthrax letters.

Case will be closed

U.S. District Judge Royce Lamberth, the chief judge of Washington's federal courthouse, made the documents public on Wednesday after consultations with a national security prosecutor.

Victims and their families were briefed on the details first, then the documents were posted on the U.S. Department of Justice website.

Taylor said the government would not normally disclose evidence against a suspect who had not been charged because of the courts' presumption of innocence, but the "extraordinary and justified" public interest in the case compelled investigators to do so.

"Had Dr. Ivins been indicted, he would have been presumed innocent until proven guilty, as is the case with any other criminal defendant," Taylor said.

"We regret we will not have the opportunity to present the evidence to a jury to determine whether the evidence establishes Dr. Ivins' guilt beyond a reasonable doubt."

He said some legal matters still have to be worked out, and then the case will be officially closed. Its closure marks the end of a seven-year investigation that involved hundreds of thousands of hours of work by the FBI, prosecutors and postal service investigators.

Ivins would have been found not guilty: lawyer

Ivins's lawyer has maintained that the brilliant but troubled scientist would have cleared his name had he lived. Some of Ivins's friends and former co-workers at Fort Detrick said they doubted he could or would have unleashed the deadly toxin.

But Taylor noted that Ivins had a history of mental health problems, and had said in an e-mail to a co-worker that he feared he might not be able to control his behaviour, and that he was having "paranoid delusional thoughts at times."

Investigators have suggested that Ivins may have been motivated by a twisted effort to test a cure for anthrax. Ivins reportedly complained of the limitations of animal testing and was developing an anthrax vaccine.

Taylor noted that Invins was under stress because the vaccine appeared to be a failure.

With files from the Associated Press