Ever since its suspect in the anthrax attacks committed suicide, the FBI has been under pressure to convince the public and the scientific community that Army scientist Bruce Ivins really was behind the 2001 attacks.
The case against Ivins rests in part on a complex genetic technique. Scientists have been asking for more particulars so they can judge for themselves, and Monday, the FBI offered more details on the science it used.
FBI scientists spent more than two hours with reporters, doing their best to explain how DNA had led them to a vial of anthrax spores in Ivins' lab. The story that emerged is this: Early on, investigators noticed something unusual about the spores sent through the mail — they were not all identical.
"The spore preparations in the envelope had a specific phenotypic variation. That means spores that looked physically different than neighbors," said Vahid Majidi, assistant director of the FBI's weapons of mass destruction directorate.
Tracing The Source
Majidi said it was like a bowl of blue M&Ms that had mixed in it a few that were brown or green or red. The fact that those were in there was like a fingerprint — potentially a way to trace the anthrax in the letters back to its source.
Investigators had collected more than 1,000 samples from labs in the United States and abroad. When they tested them, eight had the genetic fingerprint. The other samples didn't match at all.
"What genetics allowed us to do was to determine that there are eight samples out there that exactly match the letters," Majidi said. The investigations led them to RMR-1029, the name of a flask in Ivins' custody, Majidi said.
The sample had been shared with other researchers, though, and investigators say at least one of the matching samples was at a different institution entirely. About 100 people had access to those spores, Majidi said.
Ivins' lawyer said this shows the FBI's case is weak, that scores of people had access to the same mixture of spores. Majidi responded that the FBI looked at those 100 people and ruled out everybody but Ivins.
'Like Cooking A Stew'
Questions have also been raised about whether Ivins had the necessary tools in his lab to make the finely powdered spores found in some of the letters. Majidi says the answer is yes. Investigators were able to do it. The FBI says it would take one person working for three to seven days.
The only thing they were not able to reproduce was a silicon compound that showed up inside the spores used in the attacks. But Majidi said that isn't surprising; it can be hard to duplicate someone's recipe.
"It's like cooking a stew in your kitchen. It's impossible to get the exact same taste twice in a row simply because of the variations of the material you add," he said.
Addressing Scientists' Questions
Majidi said the FBI's case is "very strong." But when the FBI first began talking about the case, scientists had a lot of questions. One group even put out a list of points it wanted clarified.
Thomas Inglesby is deputy director of that group — the Center for Biosecurity at the University of Pittsburgh Medical Center.
"I have a lot of confidence in the abilities of the FBI, and they are proceeding earnestly in disclosing information and should be commended for that," Inglesby said. "But given a case of this importance to the country, and given that this kind of science has never been used in a court of law before, it's going to be important to present this scientific evidence to an independent expert review."
Inglesby was not at the briefing Monday. But he says it sounds like some of his questions have been answered. He says the FBI should publish its work in a scientific journal. The FBI says it has done some of that already and more papers are in the works.