A US scientist who killed himself last week was the sole person responsible for the deadly anthrax attacks in 2001, new FBI papers allege.
Dr Bruce Ivins alone controlled flask RMR1029, used in the attack, could not account for unusual overtime in labs and issued death threats, the FBI says.
The anthrax-laced letters killed five people, made another 17 sick, and unsettled a nation traumatised by 9/11.
Dr Ivins, 62, died shortly after being told he was about to be charged.
The FBI had been under pressure since his death to reveal the details of the investigation and its papers were unsealed by a judge on Wednesday.
FBI director Robert Mueller briefed the victims and their families about the case before publication.
In a news conference later, the US attorney for the District of Columbia, Jeffrey Taylor, said: "We consider Dr Ivins was the sole person responsible for this attack."
Overdose
The papers say Dr Ivins had possession of anthrax spores with "certain genetic mutations identical" to those used in the sole deadly biological attack on US soil.