WASHINGTON Over 1,000 possible suspects faced scrutiny before investigators finally concluded a U.S. Army scientist alone committed the deadly 2001 anthrax attacks, according to Justice Department documents released on Friday.
Officially closing its investigation, the department said various steps taken in the past year only confirmed its earlier conclusion that the scientist, Dr. Bruce Ivins, who committed suicide in 2008, had mailed the anthrax-laced letters.
The letters 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.
In seven years after the attack, an "Amerithrax task force" of investigators spent more than 600,000 work hours, conducted some 10,000 witness interviews on six continents, and recovered about 6,000 items of potential evidence.
The documents for the first time detailed the scope of the work by the FBI and other investigators in scrutinizing more than 1,000 individuals, located both in the United States and overseas, as possible suspects.
They included physicians, scientists, researchers, a disgruntled foreign scientist, a microbiologist who committed suicide after the attacks and a microbiology student with alleged ties to al Qaeda's anthrax program.
But all of those suspects, as well an another U.S. Army scientist, Steven Hatfill, who had been an early focus of the investigation, were eventually ruled out and the attention shifted to Ivins.
By 2007, investigators conclusively determined that a single-spore batch of anthrax created and maintained by Ivins at his laboratory in Maryland was the parent material for the spores in the letters.
"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 and what it called "compelling circumstantial evidence."
Ivins committed suicide on July 29, 2008, just as prosecutors prepared to charge him with murder for committing the attacks. His attorney has maintained he was innocent.
Some of the evidence involved his suspicious behavior.
"Dr. Ivins was alone in his lab for long stretches of time in the evenings and on the weekends leading up to the anthrax mailing events. This picture is in stark contrast to his behavior before and after the mailings," the department said.
It said the suicide "was the result of his final downward slide" into depression and other mental health problems.
"Dr. Ivins profound mental health struggles provide both a context for his motives to commit the crime and an explanation for how he could commit such a horrific and tragic offense," the department said in a 92-page summary.
In the months after his suicide, investigators continued to review thousands of e-mails going back 10 years and examined additional evidence.
Investigators also obtained court orders allowing access to his mental health records and interviewed mental health providers who had treated Ivins.
(Editing by Jackie Frank)