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Science falls short in anthrax investigation

Posted on behalf of Gwyneth Zakaib

When four letters containing anthrax killed five people and sickened 17 others in the United States in 2001, the Federal Bureau of Investigation (FBI) launched a massive effort to pinpoint the origin of the deadly spores.

Nine years on, there is not enough scientific evidence to provide a convincing answer, according to a National Research Council (NRC) committee report released today. The committee had reviewed the FBI’s scientific approaches and conclusions in the ‘Amerithrax’ case, as requested by the bureau in 2008 (see this Nature editorial on the need for a scientific review).

The FBI closed the case in February 2010, before the NRC review was completed, concluding that the mailer was Bruce Ivins, a microbiologist at the US Army Medical Research Institute for Infectious Diseases who committed suicide in 2008 before criminal charges could be filed.

But the NRC committee says that the evidence in the investigation isn’t strong enough to definitively link the anthrax spores in the letters to a particular flask, RMR-1029, from Ivins’ workplace.

For one thing, the repository of anthrax samples that the FBI created to compare with the envelope spores is unlikely to have been representative of the world’s stocks of that anthrax strain. Labs received unclear directions on how what documentation to provide about the source of their samples, and how they had been stored, which would make it difficult to know whether all the potential strains had been taken into account.

The FBI investigation found that certain genetic mutations in the anthrax spores in the letters were also present in the RMR-1029 sample, suggesting that this flask was the source. But the NRC report points out that RMR-1029 originally came from a mixture of anthrax cells in another lab in 1997, which could have contained all the same mutations in the parent material. The FBI should not rule out the possibility that tell-tale mutations in the mailed spores may have arisen in previous anthrax samples unconnected with Ivins, the report says.

In response, the FBI released a statement maintaining that it reached the correct conclusion in deciding Ivins was the perpetrator in this case, saying:

“…it was the totality of the investigative process that determined the outcome of the anthrax case. Although there have been great strides in forensic science over the years, rarely does science alone solve an investigation. The scientific findings in this case provided investigators with valuable investigative leads that led to the identification of the late Dr. Bruce Ivins as the perpetrator of the anthrax attacks.”

If a similar incident happened today, investigators would have faster, more accurate genetic analysis techniques at their disposal, points out Claire Fraser-Liggett, Director of the Institute for Genome Sciences in Baltmore, Maryland, who helped sequence different colonies of anthrax bacteria for the FBI. “I think we’re in a much better situation,” she says.

But others are disturbed that it’s proved so difficult to determine where the anthrax came from. “From a National Security perspective, we have a serious problem here,” says Randall Larsen, director of the Institute for Homeland Security. The report shows that potential terrorists “can reasonably assume that it will be extremely difficult, if not impossible to figure out who launched the attack.”


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