New DNA sequencing techniques convince FBI of Ivins's culpability

How strong was the case against Bruce Ivins, a leading anthrax researcher for the U.S. Army who killed himself last week after being told that the Justice Department was close to filing charges against him as the perpetrator of the fall 2001 anthrax attacks in the United States. Question about the strength of the evidence are justified, becasue the FBI was sure, for nearly five years, that they had their man — Steven Hatfill, another bioterror researcher whose lab was close to the lab where Ivins worked. Last month the U.S. government exonerated Hatfill and paid him $5.8 million compensation.

Information already publicly available suggests that the justice department expects that details to clinch the case will emerge from an unprecedented investigation over the past few years into the genetics of anthrax bacteria, using techniques not available in 2001. Sources familiar with the investigation support this idea. Shortly after the attacks, it emerged that the anthrax used was the “Ames” strain, identical to variants used in U.S. military research. Crucially, both the attack strain and samples from the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID) in Frederick, Maryland — where Ivins headed efforts to improve anthrax vaccine — had a string of 35 adenine bases (As) at the most variable region of their genomes. It was impossible, however, to narrow the suspicion down to a single lab or labs. Since then, techniques for sequencing microbial DNA have vastly improved and there has been a massive effort to sequence more anthrax samples. In April 2007 a new “ancestral” sequence for all Ames variants was posted in the public DNA database. It has 36 As at the crucial position, meaning Ames with 35 As may be less common than previously thought, and so easier to pin down. Debora McKenzie writes that the 2001 attacker used a pure, dry powder of spores. The army’s Dugway facility in Utah had made such powders since 1997 and sent samples to Ivins’s lab to be tested for viability. If the attack anthrax matches one or more Dugway batches genetically it would eliminate as suspects people without access to those batches. The Dugway powder was shipped as a wet slurry, so an attacker would have had to re-dry it. Dry powder would have been hard to contain at USAMRIID, which was not equipped to handle it. In late 2001 Ivins cleaned contamination, which confidential sources say was extensive, with anthrax matching the attack strain from his own and co-workers’ offices without initially reporting it.