Consensus Report

Review of the Scientific Approaches Used During the FBI's Investigation of the Anthrax Letters (2011)

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It is not possible to reach a definitive conclusion about the origins of the Bacillus anthracis in the mailings based on the available scientific evidence alone, this National Research Council report finds. Scientific analysis played a central role in the FBI’s investigation of the anthrax mail attacks. To help investigators narrow their search for the source of the attack anthrax, researchers used standard laboratory tests and developed new ones to characterize the physical, chemical, and biological properties of the anthrax. This report reviews the scientific approaches used during the investigation, and evaluates whether the FBI reached appropriate scientific conclusions from the use of these techniques.

Key Messages

  • The Bacillus anthracis (anthrax) in the letters was the Ames strain, and was not genetically engineered.
  • Multiple distinct colony morphological types, or morphotypes, of Bacillus anthracis Ames strain were present in the letters. Molecular assays of specific genetic sequences associated with these morphotypes provided an approach to determining relationships among evidentiary samples.
  • The FBI created a repository of Ames strain Bacillus anthracis samples and performed experiments to determine relationships among the letter samples and the repository samples. The scientific link between the letter material and flask RMR-1029 is not as conclusive as stated in the Department of Justice Investigative summary.
  • Silicon was present in the letter powders, but there was no evidence of intentional addition of silicon-based dispersants.
  • It is difficult to draw conclusions about the amount of time needed to prepare the spore material or the skill set required of the perpetrator.
  • Additional physical, chemical and radiological experiments were properly conducted to evaluate the samples for potential signatures connecting them to a source, but proved to be of limited forensic value.
  • There was inconsistent evidence of Bacillus anthracis Ames DNA in environmental samples collected from an overseas site. The committee believes that the complete set of data and conclusions concerning these samples, including all relevant classified documents, deserves a more thorough scientific review.
  • There are other tools, methods, and approaches available today for a scientific investigation such as this one.
  • Organizational structure and oversight are critical aspects of a scientific investigation. The FBI generated an organization structure to accommodate the complexity of this case and received the advice of prominent experts.
  • A review should be conducted of the classified materials that have been offered by the FBI and Department of Justice, including all of the data and materials pertaining to the overseas environmental sample collections.
  • The goals of forensic science, and realistic expectations and limitations regarding its use in the investigation of a biological attack must be communicated to the public and policymakers with as much clarity and detail as possible before, during, and after the investigation.