Where did the tin come from?
Three scientists have raised that question in a new paper that attempts to poke holes in the U.S. government's case against Bruce Ivins, the deceased Army researcher who investigators hold solely responsible for the 2001 anthrax letter attacks. The paper, to be published in the Journal of Bioterrorism and Biodefense, says the Federal Bureau of Investigation (FBI) has been unable to explain the presence of tin and silicon in anthrax spores tied to the attacks—raising questions about whether Ivins could have prepared the spores.
The authors of the paper, led by Martin Hugh-Jones, an epidemiologist and emeritus professor at Louisiana State University, Baton Rouge, speculate that the anthrax may have been weaponized—made easier to inhale—by coating it with a silicon-based compound applied in the presence of a tin catalyst. That speculation, in turn, has raised questions about whether Ivins was indeed the mailer or if he was helped by somebody else because he did not have access to the equipment required to weaponize the spores as theorized in the paper.
These are not new questions, and two of the paper's authors, Barbara Hatch Rosenberg and Stuart Jacobsen, both of whom have been vocal critics of the FBI investigation, have raised similar questions before. And the presence of silicon in the anthrax has been a subject of controversy since 2001; the issue didn't die even after scientists at Sandia National Laboratories in Albuquerque, New Mexico, established through spectral imaging that the silicon was present in the spore coat and not on the spore surface—as might be expected from an external coating.
Not only did the Sandia researchers spot silicon, they also found tin, oxygen, and iron all within the spore. The researchers, led by Sandia chemist Joseph Michael, have presented their findings at various scientific meetings since 2008, reporting the presence of all the elements found. But because silicon had always been in the investigative limelight, tin never got much attention.
Until now. The new paper puts the spotlight on tin, which the authors claim has been brushed under the carpet by FBI investigators. The FBI has "avoided public mention of the extraordinary presence of Tin," the paper says.
As recently as March 2009, however, the FBI put out a press release discussing the chemical fingerprint of the attack material, which ran through a list of elements found with the anthrax. "Spores from the letters showed a distinct chemical signature that included silicon, oxygen, iron, tin, and other elements," the release said, quoting Christian Hassell, director of the FBI Laboratory in Quantico, Virginia. "Spores from Ivins' RMR-1029 flask did not contain those elements in quantities that matched the letter spores. This is not unusual considering that Ivins' RMR-1029 preparation had been submerged in water and other chemicals since 1997 and was a mixture of 34 different spore preparations. … Although the chemical fingerprint of the spores is interesting, given the variability involved in the growth process, it was not relevant to the investigation." Instead, investigators relied on the genetic fingerprint of the attack material to link it to the flask under Ivins's control at the U.S. Army Medical Research Institute of Infectious Diseases in Fort Detrick, Maryland.
Where did the tin come from? Sandia chemist Michael says it did not have to come from an additive, as hypothesized by Hugh-Jones and his colleagues. In a study he and his colleagues did a few years ago to validate their imaging methods, they found tin—as well as trace quantities of chromium, magnesium, and other elements—in anthrax spores grown by researchers at the Lawrence Livermore National Laboratory (LLNL) in California. The LLNL researchers had cultivated the spores in controlled conditions, yet trace quantities of foreign elements still found their way into the spores. "We were surprised at first, then we realized that the elements could have come from any number of sources—lab equipment, a residual cleaning solution, some other kind of contamination," Michael says. He and his colleagues published the work in Forensic Science International in 2008.
In the new paper, Hugh-Jones, Rosenberg, and Jacobsen do not offer such a simple explanation. Instead, they speculate that the attacker or attackers may have used a process similar to one used in applying coatings in the manufacture of drugs. They don't cite any literature or documented methods for weaponizing anthrax but offer that a "procedure of this kind can be envisioned for encapsulating B. anthracis spores." They write that "the ratio of Tin to Silicon in the attack spores is 'about right' for a Tin catalyst used to produce a silicone coating, according to a chemist in the field."
The FBI's investigation has previously been criticized by a National Academies review, which concluded that the science used to implicate Ivins was not as iron-clad as the FBI had claimed. Some lawmakers have called for reopening the investigation, and the new paper—regardless of its merits—will add to mounting pressure on the government from critics.
The Department of Justice isn't budging, however. "Speculation regarding certain characteristics of the spores is just that-speculation," DOJ spokesperson Dean Boyd told The New York Times. "We stand by our conclusion."