Yet colleagues and friends of the vaccine specialist remained convinced he was innocent. They contended that he had neither the motive nor the means to create the lethal powder that was sent by mail to news outlets and congressional offices in 2001. Mindful of previous FBI mistakes in fingering others in the case, many are sceptical that the FBI has it right this time.
"I really don't think he's the guy. I say to the FBI, 'Show me your evidence,"' said Jeffrey Adamovicz, formerly of the US Army Medical Research Institute for Infectious Diseases. But investigators are so confident of Mr Ivins's involvement that they have been debating since Friday whether and how to close the seven-year-old anthrax investigation. The move would amount to a strong signal that the FBI and Justice Department think they got their man - and that he had died, excluding the possibility of a prosecution.