[Mitchell]

Possibly. But a few weeks back Keri suggested that they are beginning to believe that anthrax may mutate more rapidly than previously was thought.

Yes, that could be correct. But it's still hard to imagine rapid mutation while in the spore state. And the existence of genetic variation among the samples almost certainly would eliminate the idea that somebody simply stole a sample, doled it out into the envelopes, and mailed them out. In any case, Keim's earlier work showed anthrax to be among the most genetically stable organisms ever studied.

[Nogbad]

And the existence of genetic variation among the samples
almost certainly would eliminate the idea that somebody simply stole a sample,
doled it out into the envelopes, and mailed them out.

I think that possibility was discounted by serious people months ago.
As I have previously argued, genetic analysis is not necessary to establish that.