[keri]

With all due respect Mitchell, I think the "Brazil nut effect" is irrelevant. If all the spores were weaponized they would all very nearly be the same size. If they weren't, why would they be mixed in one container?

I can only say at this point the anthrax in FL and the DC anthrax did differ genetically. Ridge's report covered what was known at the time -- preliminary analysis revealed anthrax of the same strain -- and further genetic analysis with improved technique revealed the subtle genetic differences between the two. What those differences might mean I don't know. I don't know if they have been resolved or explained, for the private researchers cannot talk about their on-going investigation.

(I'll forgive your typos if you forgive my fatigue) Have a great evening.

[Mitchell]

Thanks very much for the information -- I appreciate it.

So there were at least two different strains of anthrax (FL and DC) and possibly a third (NY). The fact that the genetic difference between FL and DC is very small suggests that they had the same original source (making it very unlikely that there were two entire separate anthrax attacks, by two different groups with two different strains). Keim's work of a few years ago demonstrates that genetic variation in anthrax occurs naturally only very slowly. So it seems to me that there are two high-probability possibilities:

• Possibility 1. The preparer made a large batch (or multiple batches) of anthrax from the same original source. There would have to have been enough generations to yield, with high likelihood, the observed genetic variation.
• Possibility 2. The preparer intentionally induced mutations or other variation in the strain.

It's clear that the NY and DC letters are part of the same attack, because of the similarity of the letters and the handwriting. Since the NY anthrax is known to be clumpier than the DC anthrax (and therefore different from the DC anthrax), and since the FL anthrax is also known to be different from the DC anthrax [by genetic analysis], it's most likely that the NY anthrax is the same as the FL anthrax (since 2 preparations would be more likely than 3).

Also notice the different phrasings in the letters that accompanied the anthrax in NY and in DC. The two NY (lower-quality anthrax) letters said: "This is next. Take penacilin [sic] now." In contrast, the Daschle letter (with higher-quality anthrax) said: "You can not stop us. We have this anthrax. You die now." [My emphasis on the word this.] This seems to imply that this anthrax is different and more potent.