A US Army scientist who apparently committed suicide this week was close to being charged in connection with a series of deadly anthrax attacks in 2001, say federal law enforcement officials.
They said Bruce Ivins, 62, who worked for the last 18 years at government biodefense research laboratories at nearby Fort Detrick, Maryland, took an overdose of painkillers over the weekend and died on Tuesday in an apparent suicide.
A lawyer representing Dr Ivins said the scientist had fully cooperated with the government's anthrax investigation for six years, that he was innocent and they would have established that at trial.
Attorney Paul Kemp said in a statement that the relentless pressure of accusation and innuendo led to Dr Ivins' untimely death.
The finely powdered anthrax was sent through the mail to media organizations and politicians shortly after the September 11 attacks by al Qaeda militants in 2001.
The anthrax mailings killed five people, made another 17 ill, and shut down a Senate office building.
The only deadly biological attack to take place on US soil, it severely disrupted the national postal service, forcing billions of dollars in changes to its operations and turned ordinary envelopes into something to be feared.
The law enforcement officials said the death of Dr Ivins could lead to the end of the FBI's long-running and much-criticised criminal investigation.
Earlier, suspicion centered on another government scientist, Steven Hatfill, but he was not charged and the government agreed in June to pay him $US5.85 million to drop his lawsuit against the Justice Department.