Sandia National Labs, along with the FBI, has released information about the science behind the 2001 anthrax attack investigation, which helps clarify our earlier post on the topic.
In fall of 2001, the FBI considered how to best investigate the anthrax letters. The agency convened two blue ribbon exploratory panels, and Sandia’s name came up during both panels for its expertise in electron and ion microscopies and microanalysis over the range of length scales from millimeters down to nanometers. The first spore material from the letters arrived at Sandia in February of 2002.
Joseph Michael, transmission electron microscopy (TEM) lab owner Paul Kotula, and a team of roughly a dozen others examined more than 200 samples in those six and a half years. They received samples from the letter delivered to the New York Post, to former Sen. Tom Daschle (D-S.D.), and to Sen. Patrick Leahy (D-Vt.). The samples looked different, in part because of how the samples were prepared, which made examination initially difficult.
When bacillus anthracis spores are weaponized, the spores are coated with silica nanoparticles that look almost like lint under the microscope. The “lint” makes the particles “bouncier” and less likely to clump and fall to the ground. That makes the spores more respirable and able to do more damage, says Michael. Weaponization of the spores would be an indicator of state sponsored terrorism.
“Initially, scanning electron microscopy [SEM] conducted at another laboratory, showed high silicon and oxygen signals that led them to conclude that the spores were a weaponized form, says Kotula. “The possible misinterpretation of the SEM results arose because microanalysis in the SEM is not a surface-sensitive tool,” says Kotula. “Because a spore body can be 1.5 to 2 microns wide by 1 micron long, a SEM cannot localize the elemental signal from whole spore bodies.”
Using more sensitive transmission electron microscopy (TEM), Kotula and Michael’s research indicated that the silica in the spore samples was not added artificially, but was incorporated as a natural part of the spore formation process. “The spores we examined,” Kotula says, “lacked that fuzzy outer coating that would indicate that they’d been weaponized.”
Sandia’s work was the first to actually link the spore material in the New York Post, the Daschle and the Leahy letters. The elemental signatures and the locations of these signatures, while not indicating intentional weaponization, did show that the spores were indistinguishable and therefore likely came from the same source. That conclusion was corroborated a few years later by the DNA studies.
Press release: FBI unveils science of anthrax investigation…
Flashback: Anthrax Investigation Highlights Modern Biomolecular Forensic Technology…
Images: Top: Bacillus anthracis spores as viewed in SEM (left) and TEM (right). Side:Sandia’s material characterization analysts (from left to right) Joseph Michael, Paul Kotula, and manager Ray Goehner.