FBI: Homing in on the Perpetrator of the 2001 "Anthrax Attacks"

According to Fox News, the FBI has shortened its list of suspects who perpetrated the 2001 "anthrax letter attacks" to about 4, and 3 of those suspects are scientists with links to the bioweapons research facility at Fort Detrick, Maryland (USAMRIID). The 3 USAMRIID suspects are described as a former deputy commander, a leading "anthrax" scientist, and a microbiologist, whose writing samples have been obtained by the FBI. The current short list apparently does not include former "person of interest" and USAMRIID scientist Steven Hatfill.

It is presently believed that the attacks were perpetrated by placing a "weaponized" powder version of Bacillus anthracis, which was taken from Fort Detrick, inside the mailed letters. Fox News obtained an e-mail (the date of which was not provided), in which USAMRIID scientists discussed how the B. anthracis powder that was provided by the FBI for analysis was "nearly identical" to that made by a colleague, whose name was deleted from the e-mail.

The B. anthracis strain identified in the 2001 anthrax attacks belongs to the Ames strain, and its genotype (62) indicates that it was originally obtained from a dead cow in Texas in 1981. According to leading B. anthracis investigators, the Ames strain is now apparently rare in nature but is in widespread use in laboratories. Consequently it is believed that the strain of the 2001 anthrax attacks was obtained from a laboratory involved in B. anthracis study.

The big trick in the investigation has been to narrow the attack strain to a single laboratory—a very big trick, since B. anthracis generally and the Ames strain specifically are highly genetically conserved. Just last year, B. anthracis expert Paul Keim and colleagues at Northern Arizona University published their identification of 6 single nucleotide polymorphisms* (SNPs) that merely distinguish the Ames strain from other B. anthracis strains, including close genetic relatives.

However, in a March 18 letter to the Letters in Applied Microbiology, the same investigators reported that they were able to identify 6 distinct genotypes of a single B. anthracis clone (obtained from a 2005 outbreak in South Dakota) by using 4 highly mutable single nucleotide repeat (SNR) markers. SNRs are variable-number tandem repeats in the DNA sequence that exhibit very high mutation rates. The authors concluded, "SNR markers are powerful tools for detailed tracking of natural B. anthracis outbreaks and could also prove useful in forensic investigations."

It seems logical that investigators would be using (or have used) SNR markers in an attempt to subtype various Ames strain isolates from different laboratories.

*Six SNPs were highly specific for the Ames strain: 4 were on the chromosome; 1 was on the pX01 plasmid; and 1 was on the pX02 plasmid.