Trail of Odd Anthrax Cells Led FBI to Army Scientist

But what if there were something unique about the spores themselves? The anthrax experts who served as consultants weren't encouraging. Ames-strain bacteria was essentially identical wherever it was found, the advisers said.

"There is Ames and Ames and Ames," said Decker, the science team leader. If the investigators could find even one clear marker, "we'd be pretty lucky," he said.

The breakthrough the FBI sought came not from a big-name scientist but from a technician who had spent years studying anthrax bacteria under a microscope.

Terry Abshire had been tasked with growing colonies of anthrax bacteria from spores recovered from one of the mailings. When the 56-year-old Frederick resident studied the cells, she noticed that a few colonies were different in subtle ways, so she allowed the bacteria to grow for a longer period so as to check again.

"They looked different -- different colors, different textures," said Richard Langham, an FBI scientist who was assigned to work at the Fort Detrick lab. He said it was Abshire's 20 years of experience that allowed her to spot the subtleties.

"A new postdoc working with anthrax probably would not have noticed," he said.

The FBI was fortunate: Not only were there multiple mutations among the attack strain, but they also were the kinds that led to easily detectable physical changes.

Once the mutants were found, FBI scientists could begin pinpointing the subtle alterations in the spores' DNA code that caused them to morph. It took scientists until early 2004 to find all the altered genes and to develop special tests to help find the mutations in other samples of anthrax bacteria.

Even a single genetic mutation is unique, and the FBI had discovered five in the spores used in the anthrax attacks. Now investigators just needed to find the same genetic fingerprint in anthrax spores in the possession of a presumed bioterrorist, somewhere in the world.

The Search Narrows

While some FBI scientists were analyzing genetic mutations, others were scouring the planet for repositories of Ames-strain bacteria. To their surprise, Ames turned out to be quite rare, with only 15 U.S. institutions and three foreign ones possessing live, virulent Ames.

Samples of Ames were collected and added to a repository the FBI had established at Fort Detrick. In a process that ended only in late 2006, bureau scientists picked up 1,072 samples of anthrax bacteria and tested each for mutations identical to the ones in the bioterrorist's letters.

By early 2007, the FBI had a few direct hits, yet the results were perplexing. Each of the matching samples could be traced to Ivins's lab, but only indirectly. Ivins had shared anthrax bacteria with other researchers, and some of them had turned in samples containing the mutations. But Ivins's lab tested clean. He had given the FBI a vial of anthrax bacteria with no mutations.