FBI papers show a US scientist who killed himself last week was the sole person responsible for a series of deadly anthrax attacks in 2001.
Letters laced with anthrax killed five people, made another 17 sick and unsettled a nation traumatised by 9/11. Those killed were two postal workers in Washington, a New York hospital worker, a Florida photo editor and an elderly woman in Connecticut.
Dr Bruce Ivins, 62, died in hospital on Tuesday last week apparently after an overdose, shortly after being told he was about to be charged.
The FBI has been under pressure since his death to reveal the details of the investigation and the papers were unsealed by a judge on Wednesday.
Dr Ivins, 62, died shortly after being told he was about to be charged. Dr Ivins worked at the army biological weapons laboratory in Fort Detrick, Maryland.
FBI director Robert Mueller has briefed the victims and their families about the case.
US attorney for the District of Columbia, Jeffrey Taylor, said: "We consider Dr Ivins was the sole person responsible for this attack."
The papers say Dr Ivins became the focus of attention in 2007. The FBI says controlled flask RMR1029, which was used in the attack, could not account for unusual overtime in labs and issued death threats.
The papers say Dr Ivins had possession of anthrax spores with "certain genetic mutations identical" to those used in the attack.
The letters were sent to media offices and politicians on 18 September, 2001 - a few days after 9/11.