UNITED STATES:US GOVERNMENT officials insist that a troubled bioweapons scientist acted alone in anthrax attacks that killed five people, a case that centred on a near-perfect match of anthrax spores in his custody and a record of his late-night laboratory work just before the toxic letters were mailed.
Federal investigators said on Wednesday they had uncovered e-mail messages written by bacteriologist Dr Bruce Ivins describing an al-Qaeda threat that echoed language in the handwritten letters mailed to Senate offices and media organisations in September and October 2001.
Dr Ivins, who worked in high-security labs at Fort Detrick, Maryland, had a motive because of his work validating a controversial anthrax vaccine that had been suspended from production, authorities said.
Even as justice department officials declared the worst act of bioterrorism in US history all but solved, scientists and legal experts noted that the evidence was far from foolproof.
Investigators were unable to place Dr Ivins in Princeton, New Jersey, on the days when the letters were dropped into a local postbox. They did not try to match his crabbed handwriting with the distinctive block print on the 2001 letters and they did not silence congressional critics who wondered whether one man could have carried out the elaborate attacks.
Some congressional sources said the FBI case was compelling but that doubts lingered, in part because of its lengthy and ultimately fruitless pursuit of former Fort Detrick researcher Steven Hatfill. In June, the justice department agreed to pay Mr Hatfill a $5.8 million settlement to resolve his privacy lawsuit.
Paul Kemp, a lawyer for Dr Ivins, said prosecutors had carried out "an orchestrated dance of carefully worded statements, heaps of innuendo and a staggering lack of real evidence - all contorted to create the illusion of guilt."
Authorities said they were compelled to present their case against Dr Ivins, who had been warned that he could face murder accusations but had not been charged, because of the "extraordinary public interest" after his death on July 29th by suicide.
Using sophisticated DNA techniques and gumshoe detective work, FBI agents and US postal inspectors picked apart discrepancies in Dr Ivins's accounts about the lethal bacteria he had cultured. Prosecutors say he offered different stories about when and how he learned that the anthrax cultures in his lab genetically matched the powder in the letters.
The FBI accused him of submitting "questionable" anthrax samples five years ago to keep investigators off his trail.
Investigators homed in on Dr Ivins for several reasons, according to a sworn statement last year from postal inspector Thomas Dellafera. Mr Dellafera said Dr Ivins could not justify his "late-night laboratory work," which peaked about the time of the mailings on September 18th and October 9th, 2001.
Authorities also made reference to e-mails Dr Ivins sent to a friend describing his rising stress loads, depression and feelings of "isolation - and desolation" in 2000 and through the September 11th, 2001, terrorist attacks.
- Los Angeles Times-Washington Post service