Trail of Odd Anthrax Cells Led FBI to Army Scientist

But while bureau officials view the evidence against Ivins as overwhelming, any chance at full certainty was lost when Ivins took his own life in July, said Ed Montooth, the FBI special agent in charge of the investigation the bureau dubbed "Amerithrax."

"We were truly disgusted after we knew he had killed himself," Montooth said, "because we knew the only way we'd have justice was to be in court."

Ivins's 'Ultimate Creation'

It was intended for garden-variety animal experiments, but the collection of anthrax spores known as RMR-1029 was anything but ordinary. Ivins, its creator, had devoted a year to perfecting it, mixing 34 different batches of bacteria-laden broth and distilling them into a single liter of pure lethality.

The finished product, a muddy, off-white liquid in a glass flask the size of a small coffee pot, was the greatest single concentration of deadly anthrax bacteria in the country, FBI investigators said.

Ivins began work on it in 1996 with the goal of creating a large repository of highly virulent Bacillus anthracis spores that could be used by his fellow scientists at the U.S. Army Medical Research Institute for Infectious Diseases, or USAMRIID, for years to come. To measure the effectiveness of new anthrax vaccines, the drugs have to be tested against a potent form of bacteria that remained the same from one experiment to the next.

The art of "spore preparation" is a tedious job often relegated to novices and technicians. But Ivins, a veteran researcher with decades of experience, was naturally good at it, according to FBI officials and USAMRIID scientists. With RMR-1029, Ivins established an anthrax gold standard.

"It was his ultimate creation," said Jason D. Bannan, an FBI microbiologist assigned to the Amerithrax case. "This was the culmination of a lot of hard work."

But Ivins could not have known that RMR-1029 contained genetic mutants, in relatively high numbers. A batch of spores like RMR-1029 might be expected to contain, at most, one mutated variant. But Ivins's flask, because of its unusual pedigree, contained five.

Without knowing it, Ivins had provided the FBI a rare clue that in time would lead them to his lab.

The Hunt for Mutants

Within days after letters laden with anthrax microbes reached New York and Washington, Fort Detrick had become the scientific epicenter of the FBI investigation. It had a resident corps of anthrax specialists as well as numerous biocontainment laboratories where deadly microbes could be handled. Dozens of the lab's white coats -- including Ivins -- joined FBI scientists in the search for the culprit.

The experts quickly established that the attacker had used the so-called Ames strain, a virulent form of anthrax bacteria that was the strain of choice within the Army's biodefense complex. They also concluded, by November 2001, that the attack strain had not been altered: The spores were not drug-resistant and contained no foreign additives to make them more lethal. It was a detail the FBI would not disclose publicly for six years.

Top FBI officials hoped that science could provide a link to the bioterrorist, but they soon grasped the difficulty of the task. They searched for traces of human DNA in the anthrax powder, and in the envelopes, but found none.