To start, I have believed all along that Iraqi intelligence had their dirty hands on this event. Based on ISG findings that Iraq had apparently decided in 1994 to not attempt production, but rather only research to enhance "break-out" capability and that the Iraqi and Syrian intelligence services had formed an alliance to develop the field "in chemical and biological of mutual interest," I now suspect that Syria made the anthrax product with Iraqi Intelligence assistance. The cooperation included Iraqi scientists assisting the Syrians.
Much of what these authors say, I can verify. Iraq had air-freighted into Baghdad two Niro spray dryers that were of the type that would yield "plus or minus any particle size" the producer desired. One of these was located at Al Hakam and was destroyed under UN supervision in May/June 1996. The other one we were unable to locate (and, of course, Iraq did not know its whereabouts) until spring 1998. Within two weeks I had a sampling team in Iraq to thoroughly sample the 2nd dryer. Unfortunately, Iraq suddenly had an urgent need for the dryer and had thoroughly disassembled it, cleaned and sterilized it and then reassembled it. We were not able to get permission to destroy it but we kept tabs on it. However, UNMOVIC never checked for it and I believe the US did not after the war. It very well could have been moved to Syria .
Iraq did import 200 metric tonnes of aerosil from Germany in 1988. The silica was for the CW/BW weapons group. We, UNSCOM, believed the silica was intended for making dusty chemical agents, but it could also have been used for BW weapons. We know that Iraq had all the aerobiology technology necessary. It appears that the UN FAO also obtained 25 metric tonnes for Iraq "drug industry" in 2002 (of course this was after the anthrax letters). This also was not checked by UNMOVIC.
There is evidence that the Pasteur Institute in Paris had the Ames strain. We know that Iraq obtained from the Pasteur Institute several strains of anthrax but we were only able to confirm the identity of one strain (Pasteur A15, I believe. I could check it.) Thus one of the other strains might have been the Ames strain; in addition to the two possible sources cited by the authors.
Thus, the authors seem to have done a rather thorough analysis that the FBI should have done. There are some minor flaws in their data but I have not checked against their sources. There is no doubt that the material in the Daschle and Leahy letters as well as the AMI building contained a hydrophilic silica. The polyglass binder came from the FBI itself. I have learned of the addition of the weak like-charge from several sources including some on the inside of the investigations. The pharmaceutical industry is interested in this because, as the authors state it also increases retention of the small particles in the lung. Normally this retention is around 40%, but the like-charge increases this approaching 100%. I suspect this was the interest of whoever did this.