Review of the Scientific Approaches Used During the FBI's Investigation of the 2001 Anthrax Letters (2011) / Chapter Skim
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4 Physical and Chemical Analyses
4 Physical and Chemical Analyses
Pages 75-96
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From page 75... ...
4.2 SPORE PREPARATION AND PURIFICATION One line of inquiry in the FBI investigation concerned the expertise, time, and technology needed to produce the material used in the attacks. That is, what skills, tools, or procedures would be needed to cultivate, purify, and dry the spores, and how long would the entire process take?
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From page 76... ...
Nonetheless, the Bureau inves tigated individuals without regard to their specific skill sets. The FBI further stated that the time for preparation and equipment used in preparation of the letter materials was difficult to ascertain because of numerous variables.
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From page 77... ...
, any of which could require several hours to several days. Drying of surrogate spore preparations using various TABLE 4-2 Estimates of Media Volume Required for Spore Preparation Total spores needed for Spores prepared on plates at 8 × 109 spores/plate all letters Spores prepared in liquid 1012 Low estimate = 3.7 × 463 plates 2.8 liters in a fermentor, based on Heine's (2010)
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From page 78... ...
anthracis from the Leahy letter as the starter source) (FBI Documents, B1M13D3)
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From page 79... ...
The Daschle and Leahy letter samples had bimodal particle size distributions, with one mode around 1.5 µm in diameter, corresponding to the size of an individual B anthracis spore, and another mode greater than 20 µm in diameter, corresponding to the size of clusters of large numbers of spores and other material 1 To remove the implication that autoclaving of letter samples was standard practice, the word "untreated" has been inserted into this sentence.
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From page 80... ...
Particle size distributions for the Dugway surrogate samples were reported as mean particle diameter, which unfortunately is a less informative indicator of particle size when the distribution is bimodal. Nonetheless, many of the Dugway preparations gave mean particle diameters in the same range as the letter samples, 2 to 4 µm, consistent with the notion that dispersants were not required to produce powders with these particle size distributions (DPG, 2006)
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From page 81... ...
dissolved in aqueous solution Scanning electron microscopy with energy Size-resolved elemental composition of a dispersive X-ray analysis (SEM-EDX) solid sample, with size resolution of about 1 µm or less Nanometer secondary ion mass Size resolved elemental and molecular spectrometry (nano-SIMS)
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From page 82... ...
Silicon dioxide remained a possibility and was investigated using SEM-EDX to probe the spatial distribution of elements in the samples. TABLE 4-4 Summary of Silicon Measurements in Evidentiary and Surrogate Samples Bulk silicon content SEM-EDX SEM-EDX % spores Samplea ICP-OES Analysis with Si in coat Leahy 1.4-1.8% 1-2% per spore 97/124 = 76% Daschle 1-2% per spore 73/111= 66% 10% 1-2% per spore 91/141 = 65% New York Post RMR-1029 0/98 = 0% 0/115 = 0% 0/191 = 0% RMR-1030 (shake 6/94 = 6% flask preparation)
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From page 83... ...
These results indicate that it is possible to prepare spores having a silicon content in the range of the Leahy letter sample without adding a dispersant (FBI Documents, B1M7)
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From page 84... ...
When this sample was mounted and analyzed in the same manner as the letter samples, silicon dioxide nanoparticles were clearly observed on the spore surface. Although this experiment indicates that a dispersant would have been detected if it were present in the sample, a more definitive experiment would have been to spike an actual letter sample with dispersant at levels comparable to the bulk silicon content.
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From page 85... ...
anthracis Ames strain spore preparation pro duced by and housed at USAMRIID. RMR-1030 did not resemble RMR-1029 or the letter spores in its physiochemical or genetic properties (FBI letter to the committee, December 7, 2009)
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From page 86... ...
Measurements were performed on a total of 57 spore samples that included existing samples provided by the Depart ment of Homeland Security and collaborating laboratories (Weber, 2009; FBI Documents, B1M1D7)
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no silicon was detected in the form of a dispersant in the exosporium. The bulk silicon content in the Leahy letter could be completely explained by the amount of silicon incorporated in the spores during growth.
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Detection of diatrizoate and meglumine in purified spore samples was first demonstrated with control samples of B cereus spores (FBI Documents, B1M12)
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In a validation study (FBI Documents, B1M10) , the agar and blood agar analyses were highly sample dependent and too sensitive to experimental condi tions for the FBI to draw any conclusions from these studies.
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From page 90... ...
and infrared spectroscopy to detect VOCs. Headspace GC-MS was performed only on the Leahy letter sample.
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It is apparent that the high δ18O value is inconsistent with the rest of the spore samples analyzed. In an attempt to understand the rela FIGURE 4-2 Stable isotope results 18O versus 2H.
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From page 92... ...
All gave consistent values around −45‰ for δ2H and −7.5‰ for δ18O. These results proved useful in providing starting water isotopic ratios as input for the interpretation of the spore sample isotopic ratios presented in Section 4.10.1 (FBI Documents, B1M9D1)
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From page 93... ...
The FBI further stated that there were too many variables to be able to quantify the time or specify the equipment used to prepare the letter materials. However, FBI officials indicated that inferences about required skills or time for spore preparation were never the sole criterion for eliminating suspects (FBI/USDOJ, 2011)
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From page 94... ...
Electron microscopy, aerosol particle size analysis, and bulk and spatially resolved elemental compositions were appropriate first steps for characterizing the samples. Follow-up experiments to determine the spatial distribution of silicon in letter material and the mechanism of silicon uptake also were appro priate, as were efforts to search for possible elemental and molecular signatures.
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From page 95... ...
Surrogate preparations showed that samples having bulk silicon content up to 5 percent could be prepared without intentional addition of silicon dispersant. However, none of the DPG surrogate preparations analyzed for silicon in the spore coat were similar to the New York Post, Daschle, and Leahy letter samples with respect to either the amount per spore of silicon incorporated in the coat or the fraction of spores observed to contain silicon in the coat.
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From page 96... ...
SEM-EDX measurements showed no silicon in the coats of spores taken directly from RMR-1029, whereas the majority of spores analyzed from the New York Post, Daschle, and Leahy letter materials contained silicon in the coat. Based on recent studies of the mechanism of silicon incorporation, silicon could have been incorporated in the coats of the letter spores only if spores from RMR-1029 were subjected to one or more subsequent growth steps.
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