WASHINGTON - A National Research Council committee asked to examine the scientific approaches used and conclusions reached by the Federal Bureau of Investigation during its investigation of the 2001 Bacillus anthracis mailings has determined that it is not possible to reach a definitive conclusion about the origins of the anthrax in letters mailed to New York City and Washington, D.C., based solely on the available scientific evidence.

Findings of the committee's study include:

  • The FBI correctly identified the dominant organism found in the letters as the Ames strain of B. anthracis.
  • Silicon was present in significant amounts in the anthrax used in the letters. But the committee and FBI agree that there is no evidence that the silicon had been added as a dispersant to "weaponize" the anthrax.
  • Spores in the mailed letters and in RMR-1029, a flask found at the U.S. Army Medical Research Institute for Infectious Diseases (USAMRIID), share a number of genetic similarities consistent with the FBI finding that the spores in the letters were derived from RMR-1029. However, the committee found that other possible explanations for the similarities -- such as independent, parallel evolution -- were not definitively explored during the investigation.
  • Flask RMR-1029, identified by the U.S. Department of Justice as the "parent material" for the anthrax in the attack letters, was not the immediate source of spores used in the letters. As noted by the FBI, one or more derivative growth steps would have been required to produce the anthrax in the attack letters. Furthermore, the contents of the New York and Washington letters had different physical properties.
  • Although the FBI's scientific data provided leads as to the origin of anthrax spores in the letters, the committee found that the data did not rule out other possible sources. The committee recommended that realistic expectations and limitations regarding the use of forensic science need to be clearly communicated to the public.
  • Further development and validation of methods for analyzing environmental samples might have benefited this investigation and will be important in future investigations.

Following a required FBI security review of the committee's draft report in October 2010, the bureau asked to provide the committee with additional materials and briefings about its investigation. From these materials the committee learned more about the organization and oversight of the scientific investigation and about the collection and analysis of environmental samples.

Included in the new materials were results of analyses performed on environmental samples collected from an overseas site. Those analyses yielded inconsistent evidence of the Ames strain of B. anthracis in some samples. The committee recommends further review of the investigation of overseas environmental samples and of classified investigations carried out by the FBI and Department of Justice.

"The committee commends the FBI for reaching out to the scientific community for assistance early in the anthrax letters investigation," said Alice P. Gast, chair of the committee and president of Lehigh University, Bethlehem, Pa. "We believe this independent review -- done at the FBI's request -- will help strengthen the law enforcement and national security community's scientific and analytical capabilities in future investigations."

Immediately following the 2001 anthrax attacks, there was no clear organizational structure to assist the FBI in pursuing the scientific investigation. Over the course of its inquiry, the FBI worked to develop one. It found and engaged highly qualified scientists from both the government and private sector to give expert scientific advice on anthrax and the attacks. The bureau appropriately decided to establish a repository of the Ames strain of B. anthracis gathered from laboratories around the world against which to compare the anthrax used in the 2001 mailings. But problems with the repository, the committee found, limited the strength of conclusions that could be made using it.

During the last decade, new "molecular" scientific methods and insights relevant to this investigation also became available. "Using tools such as high-throughput, 'next generation' DNA sequencing could have strengthened or weakened the association between spores found in the mailed letters and spores from RMR-1029," said David A. Relman, vice chair of the committee and Thomas C. and Joan M. Merigan Professor, Stanford University School of Medicine, Palo Alto, Calif. "Such new technology will be important to similar investigations in the future."

The Research Council was asked to consider facts and data surrounding the scientific investigation based on documents and oral presentations provided by the FBI and others. Judging the conduct of the law enforcement inquiry was beyond the scope of this study. The committee was neither asked for nor offers findings on the possible guilt or innocence of individuals connected with the 2001 B. anthracis mailings. Moreover, authors of this report did not review classified materials about the case. Thus, they cannot comment on how classified information may have influenced the course of the FBI's inquiry, including the scientific investigation.