Trail of Odd Anthrax Cells Led FBI to Army Scientist

Ivins normally worked with liquid anthrax spore solutions, not dry powders, investigators acknowledge. Ivins's colleagues insist that he had no experience with "dry aerosols" of anthrax spores and would not have known how to make them.

But drying the spores turned out to be no obstacle at all, FBI scientists said. It required only one more step, using a common laboratory machine known as a lyophilizer. Ivins had one in his lab.

"Because he grew spores on a daily basis, he was in a position to make [the powder], and no one would be the wiser," Montooth said.

Would the FBI's evidence have stood the challenge of a court trial? Paul Kemp, a lawyer who represented Ivins, dismissed the government's case as an "orchestrated dance of carefully worded statements, heaps of innuendo and a staggering lack of real evidence."

Bureau officials said they feel cheated at being deprived of the opportunity to prove otherwise. The resentment spilled over in the early hours of July 27, when investigators first learned of Ivins's drug overdose, said Montooth, who recalled getting 253 text messages from fellow agents within minutes after the news broke. For the next week, the members of his team barely slept, Montooth said, because they knew Ivins's suicide meant they "would never get to do what we wanted to do, which was to go to court."

The only solace, he said, came on the day the Amerithrax team sat down with family members of the victims of the attacks. In an FBI conference room, Montooth laid out the still-secret details of the seven-year investigation.

"They thanked us," Montooth said, recalling the families' reaction. "They said, 'We believe you got the right guy.' "

Staff researcher Julie Tate contributed to this report.