These tests led to the conclusion that two separate production batches of anthrax were used for the New York and Washington, D.C. mailings because each contained differences in spore concentrations, color, contaminants, texture, growth media remnants, and observed debris. When coupled with the genetic analysis discussed in Section B, infra, investigators were able to conclude that the two distinct batches of anthrax used in the 2001 attacks shared a common origin.
Elemental mapping, using electron microscopy, detected an amorphous layer of silicon and oxygen below the exosporium, which was localized to the spore coat. This layer was present in the spores mailed to New York and the spores mailed to Washington, D.C., albeit in slightly different quantities.
The scientific review panels also assisted investigators in reaching three key conclusions. First, the perpetrator of the 2001 anthrax mailings acquired the Ames strain of anthrax from a laboratory, rather than from a new sample collected from a naturally occurring outbreak. The Ames strain has been isolated only once in nature, that being from a dead cow in Sarita, Texas in 1981. A second natural occurrence of the Ames strain in the environment has not been reported. Only 15 U.S. and three foreign laboratories were known to possess the Ames strain of anthrax prior to the attacks.
Second, the evidence demonstrated that the perpetrator was familiar with key items of laboratory equipment used in microbiology research. All of the Ames anthrax existing in the 15 U.S. labs prior to the attacks was in liquid slurry form or on vegetative cell slants, rather than in powder form. Consequently, it was not possible for the perpetrator to merely steal an existing quantity of Ames spore powder “off the shelf,” because none was known to exist in the holdings of any laboratory. Even if the perpetrator stole a quantity of liquid Ames anthrax slurry, it would still have been necessary to dry the anthrax in order to produce a product like the one recovered from the envelopes. This drying procedure would have required either the type of laboratory equipment, such as a lyophilizer or speed-vac system, that was present in each of the 15 labs, or considerable time and space to air-dry. Alternatively, if the perpetrator stole only vegetative cells or a small quantity of spores to use as seed stock, not only would the perpetrator have to dry the anthrax, he would also have to subject the anthrax to two separate culturing and washing operations using an incubator and centrifuge.
Third, the perpetrator almost certainly came into contact with aerosolized anthrax spores in committing the crime, and was probably protected against an anthrax infection by vaccination and/or antibiotics. One point of contact between the perpetrator and the anthrax spores occurred as the anthrax-laden envelopes were deposited into the mailbox. According to scientists, even assuming that the letters were transported to the mailbox in a sealed plastic bag or other containment device, the act of removing them from the bag or letting them drop from a bag into the mailbox would have generated sufficient kinetic energy to aerosolize some spores through the pores in the envelopes. A second likely point of exposure occurred as the perpetrator loaded the letters and envelopes with anthrax powder. Even if a sophisticated or improvised containment
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