New Questions About the FBI’s Anthrax Case: Valid Concerns or Red Herring?

Was specialized equipment necessary to make the deadly powder used in the 2001 letter attacks, and, if not, what does that say about the ability of terrorists to perpetrate such attacks in the future?

Envelopes containing spores that cause anthrax
were mailed in September and October 2001.

According to recent press accounts, new evidence has called into question the Federal Bureau of Investigation’s (FBI) claim that the late Dr. Bruce Ivins, a microbiologist at the US Army Medical Research Institute of Infectious Diseases (USAMRIID) at Fort Detrick, Maryland, was solely responsible for the anthrax letter attacks in the fall of 2001 that sickened twenty-two people and killed five. Because Ivins committed suicide shortly before he was to be indicted for the crime, the evidence against him was never tested in a court of law.

The latest challenge to the FBI’s case against Ivins comes from depositions given by some of his former USAMRIID colleagues in a suit against the US government filed by Maureen Stevens, whose late husband, Robert Stevens, was the first victim of the anthrax letter attacks. Stevens worked in Boca Raton, Florida, as a photo editor for American Media, Inc., the publisher of the supermarket tabloid the Sun. He died of anthrax on October 5, 2001, after having been exposed to a letter containing deadly Bacillus anthracis spores. (The actual letter was never found.) The lawsuit brought by Stevens’s widow claims that by failing to secure the stocks of B. anthracis bacteria stored at USAMRIID, the US government was negligent. Although at first glance the court documents appear to raise serious doubts about the FBI’s case against Ivins, the scientists’ claims are based on assumptions that may well be false.

[Editor’s note: Jonathan Tucker died suddenly in late July, just days after submitting this article for publication. Jonathan was a valued member of the editorial board of the Nonproliferation Review. For many years before that, when he worked for the Center for Nonproliferation Studies, he served as an associate editor. Although I did not know him as well as many of my colleagues, in part because we never worked together in the same locations, we had a long and productive working relationship. I will always remember Jonathan as unfailingly professional and conscientious. I greatly valued his suggestions for topics and authors to pursue as well as, of course, his own articles, the most recent of which we published in November 2009. Jonathan wrote lucidly and quickly, and had the rare gift of being able to speak to the expert community on chemical and biological weapons and public health issues—a community of which he was a leading and valued member—while simultaneously making important but often complicated subjects readily understandable to non-specialists.On July 18, I e-mailed Jonathan, asking if he would like to write a short article for this online publication about some interesting developments regarding Bruce Ivins, the government scientist formally identified by the FBI as the suspect behind the 2001 anthrax mailings. Jonathan responded less than an hour later, saying he was “of course interested in the Ivins case” and requesting the opportunity to review the new documentation. Once he did, Jonathan generously agreed to write up his analysis, sending me his submission two nights later. He died before we finalized the article, but as was always the case with Jonathan’s writing, it required very little editing. It is one more example of Jonathan’s many analytical contributions to the field over the years. Despite the sad circumstances, we are pleased to publish it.
— Ronnie D. Terrell]

The Anthrax Letters

The 2001 anthrax attacks remain the only fatal bioterrorism incident to have occurred in the United States. Shortly after the al Qaeda attacks of September 11, 2001, a perpetrator mailed the tainted letters in two waves. The first set of letters, postmarked September 18, was sent to media outlets in New York City and Florida; letters in the second set, postmarked October 9, were addressed to two US senators in Washington, DC—Tom Daschle (D-South Dakota) and Patrick Leahy (D-Vermont).

Four letters containing B. anthracis spores were eventually recovered: two from the first wave, and two from the second. Physical examination of the spore preparations revealed a clear difference in quality between them: the powder from the New York letters was brownish and relatively coarse, while that from the Washington letters was finer and dispersed more readily. The differences between the two preparations have been attributed to variations in factors that affected their production, such as differences in humidity, temperature, and culture media.

Though finer, the powder in the second batch of letters did not consist of loose, individual B. anthracis spores alone but also included clumps of several spores. As the letters passed through high-speed mail sorting machines, these agglomerates broke into smaller particles. The microscopic spores then leaked through pores in the envelopes, infecting postal workers and others who came in contact with them. By cross-contaminating other pieces of mail, the escaped spores were transported to other victims.

Although the B. anthracis strain used in the letter attacks was quickly identified as the Ames strain, a highly virulent strain employed in biodefense research, its precise source was unknown. In an effort to trace the spores back to the original source, the FBI collected samples of the Ames strain from all laboratories in the United States known to be working with it. Scientists under contract to the FBI then performed advanced genetic testing to find a match between the laboratory samples and the letters’ B. anthracis, which had four unusual mutations. Of the more than one thousand samples of the Ames strain that the FBI collected, only eight had all four genetic mutations matching those in the mailed spores. These eight samples were traced back to a single flask of B. anthracis spores at USAMRIID, labeled RMR-1029, which Ivins had prepared for the testing of a candidate human vaccine in animals.

Once the results of microbial forensic analysis had narrowed the pool of possible suspects down to the roughly one hundred people who had access to RMR-1029, the FBI used traditional police investigative methods until all suspects were excluded, except one—Ivins. As for the motive, the FBI believed that because the safety of Ivins’s anthrax vaccine had been called into question in 2000, casting doubt over the future of his research, he had sought to heighten fears of bioterrorism by staging an actual attack.

Despite the close genetic match between the spores recovered from the letters and those in RMR-1029, some of the chemical constituents of the powdered spores found in the mailings, such as a high level of silicon, were not present in the source material. This indicated that the bacteria in the RMR-1029 flask had not been used directly for the letter attacks but had been grown in a separate culture medium, purified, concentrated, and processed into a powder. According to the theory of the case developed by the FBI, in the days preceding the two sets of mailings, Ivins had worked late at night and on weekends in the high-containment suite at USAMRIID to grow and dry the spore preparation. Nevertheless, because no spores were ever found in Ivins’s home or car, and no eyewitness saw him mail the letters from a mailbox in downtown Princeton, New Jersey, the FBI’s case was entirely circumstantial.

Questions Raised in the Depositions

The depositions taken from USAMRIID scientists and technicians as part of the lawsuit by Maureen Stevens were first disclosed on July 18 in a joint article by three news organizations: PBS Frontline, ProPublica, and McClatchy Newspapers. According to the article, testimony in the court documents suggests that Ivins did not have access to the specialized equipment and know-how he presumably would have needed to dry the spores into the high-quality powder sent through the mail, raising doubts about whether he was technically capable of committing the crime.

  • Microbiologist Patricia Worsham stated in her deposition that the existing facilities at USAMRIID could not have been used to produce a preparation of dry B. anthracis spores. “We did not have anything in containment suitable for drying down anything, much less a quantity of spores,” she said. “The lyophilizer [freeze-dryer] that was part of our division was in non-containment. If someone had used that to dry down that preparation, I would have expected that area to be very, very contaminated, and we had non-immunized personnel in that area, and I might have expected some of them to become ill.” Worsham also noted, “I have not seen any evidence of anyone [at USAMRIID] getting any training that would allow them to … produce dried material of that quality.”
  • Another USAMRIID scientist, Susan Welkos, said, “We don’t work with powders, just liquids, and in relatively small volumes. We don’t have the expertise to—to scale up and manufacture some kind of powder.” When asked if she thought Ivins had the necessary expertise, Welkos replied, “No. I don’t believe he did.”
  • A technician at USAMRIID, Stephen Little, stated that the lyophilizer in Ivins’ laboratory was outside the containment area and too large and heavy for him to move by himself into the air lock. Moreover, if Ivins had worked with dried powders of B. anthracis spores, the equipment would have been heavily contaminated, requiring the decontamination of the entire suite with heated paraformaldehyde gas—a complex and hazardous operation that must be performed overnight by building engineers, who keep meticulous records. When Little was asked if anyone at USAMRIID had the expertise to produce large quantities of dried B. anthracis spores, he replied, “Not large quantities at USAMRIID, no.”

Analysis of the Statements

While the scientists’ depositions appear compelling at first glance, many of the statements are misleading. First, much has been made of the specialized knowledge needed to prepare dry powders of B. anthracis spores, yet this factor may have been exaggerated. Early reports that the spores contained a high level of silicon suggested that they could have been deliberately “weaponized” by coating them with silica to reduce static clumping and facilitate their delivery as a fine-particle aerosol. FBI scientists later determined, however, that the silicon was not on the surface of the spores but had been incorporated into an inner layer called the endosporium when the anthrax bacteria were grown and induced to sporulate. Thus, Ivins would not have needed weapons-related expertise to process the spores.

Second, the depositions by Worsham and Little imply that the only way to produce significant quantities of dried B. anthracis is by using a lyophilizer, yet lower-tech approaches may also be feasible. On August 18, 2008, Dr. Vahid Majidi, the assistant director of the FBI’s WMD Directorate, gave a press briefing on the science behind the anthrax investigation. When asked about the process used to dry B. anthracis spores, he replied, “I think that a lot of folks focus on the issue of [the] lyophilizer. You can ask any of the folks and the panel members, and they will tell you that you can dry biological samples in one of dozens of ways. Lyophilizer is one of them. You can let the samples heat-dry. You can let … the water evaporate.”

The fact that the B. anthracis powder mailed to the two senators was so buoyant and dispersed so readily led many observers to conclude that it had been deliberately weaponized. Majidi said that this false belief resulted from the fact that very few scientists have experience with preparations of dried bacteria. Another official present at the FBI press briefing agreed, noting, “There is a misconception … that very simple spore preparation[s], simply spores washed in water, when dried, are not dangerous and friable.”When a reporter asked whether such a simple dried spore preparation would have to be milled, Majidi said no, although he declined to provide details of the process for security reasons. However, in response to the question whether the equipment in Ivins’s lab would have been sufficient to grow and dry the spores, Majidi said, “It would have been easy to make these samples at RID [USAMRIID].”

During the press briefing, FBI officials estimated that making the preparation of powdered B. anthracis spores could have taken one person between three and seven days of work. They also corrected false reports that the FBI had been unable to reverse-engineer the highly refined B. anthracis powder mailed to the two senators. When asked if the FBI’s powder behaved the same as the material in the letters, Majidi replied, “as far as our preparation goes, we were able to repeat almost everything except the silicant signal [the high silicon content of the spores]. … Can we make the same spore purity? Yes. Can we make the spore dry? Yes.”

Based on this information, it appears that Ivins could have dried the spores without the need for a lyophilizer by using a low-tech method, such as heat-drying the concentrated slurry on glass plates and then harvesting the dried material inside a sealed glove box. Indeed, the brownish discoloration and coarse texture of the first spore preparation suggest the use of a crude production method. The fact that the second spore preparation was so much better than the first may mean that Ivins was able to move quickly up the learning curve through a process of trial and error.

In sum, public statements by Majidi and other senior FBI officials suggest that the assumption underlying the more recent statements of the USAMRIID scientists—that specialized equipment, expertise, and tacit knowledge are required to produce a lethal preparation of dry anthrax spores—may be incorrect or at least exaggerated. Other analyses of this issue have been more equivocal, however. In February 2011, an expert committee convened by the National Research Council, the policy analysis arm of the US National Academy of Sciences, issued a report on the science behind the FBI’s anthrax investigation. The panel admitted, “Given uncertainty about the methods used for preparation of the spore material, the committee could reach no significant conclusions regarding the skill set of the perpetrator.”


Although the FBI’s circumstantial case against Bruce Ivins will never satisfy hard-core skeptics and conspiracy theorists, the mosaic of evidence is fairly convincing when viewed as a whole. At the same time, it is far from certain that a federal prosecutor could have persuaded a jury of Ivins’s guilt “beyond a reasonable doubt.” If the FBI is correct and Ivins did not need specialized equipment and know-how to make the highly refined preparation of dry B. anthracis spores that was mailed to the two senators, then the security implications are deeply troubling. In that case, producing a potent biological weapon agent involves far fewer technical hurdles than is generally believed, making this lethal technology relatively accessible to those with malicious intent.

Jonathan B. Tucker was the manager of the Biosecurity Education Project at the Federation of American Scientists. His edited book on the security challenges of dual-use technologies and how best to govern them, Innovation and Security: Preventing the Misuse of Chemical and Biological Technology, will be published by MIT Press in 2012.

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