Dr. Bruce Ivins, a US Army Scientist, who committed suicide in 2008, has been held responsible for mailing the anthrax-laced letters, which killed five people, sickened 17 others, jolted a nation reeling from the September 11 hijacked-plane attacks and resulted in one of the FBI's largest investigations ever.

Over 1,000 possible suspects had to face the scrutiny before "Amerithrax task force" of investigators finally concluded that Ivins, a biologist at the Army's Fort Detrick biodefense lab in Frederick alone committed the deadly attacks.

Some 10,000 witness interviews on six continents, more than 600,000 work hours, and about 6,000 items of potential evidence acquired, all went behind the investigation of the 2001 anthrax attacks.

"The evidence gathered in this seven-year investigation establishes that Dr. Bruce Ivins was the anthrax mailer", according to the documents, citing direct evidence about the anthrax spores.

The Justice Department officially ended its eight-year investigations with the release of hundreds of pages of documents that starkly portray the mental unraveling of the deceased Army scientist accused of committing the worst act of bioterrorism in U.S. history.