I did not attend either FBI briefing, and the comments below relate to multiple news reports of the briefing.
1. Either one flask or two contained the specific anthrax strain in the letters--it was reported both ways in different newspapers, and apparently there was disagreement at the meeting.
2. Two labs had this strain, but the name of the other lab is still a secret. Why? Was it a lab that manufactures anthrax in powder form, and thus might be easier to link to the crime than the USAMRIID lab, which officially uses liquid anthrax only?
3. Yes, 100 people did have access to the strain--but FBI ruled every one of them out, leaving Ivins as the sole suspect.
4. FBI says it did re-engineer the powder, and it had the same properties as the anthrax found in the Leahy/Daschle letters--but the easily produced, engineered powder did not contain extra silicon, as reported by the Armed Forces Institute of Pathology for the letter anthrax. No explanation was provided, making the FBI claim questionable.
5. No one reported on the mix of B. cereus and B. anthracis that was previously said to provide evidence of where the anthrax came from.
The additional scientific information reported fails to clarify any of the persisting questions in the case. Many other people had access to this strain, and the science is unable to pin it on any one individual.
Maybe the FBI unequivocably ruled out 100 people as the lone suspect, by an inability to place them at the mailing sites, for example. But despite two lame attempts last week to make it appear Ivins could possibly have mailed the letters in Princeton (the first claim putting him at the mailbox too early for the postmark), there has still been no evidence presented establishing he made such a trip.
However, if you concede that the letter attacks are much more likely to have been the work of more than one individual, then the 100 people "ruled out" by FBI (using unreleased criteria) jump back in as suspects. Because perhaps all one of them had to do was to supply a tiny amount of anthrax to someone else who produced the final product. It would be very hard to rule that out.
Furthermore, we know how readily the spores leaked out of envelopes. The person who mailed the Daschle/Leahy letters had to have contaminated themself, simply by the act of placing the letters in a mailbox. This contamination should have extended to their vehicle (unless they showered and changed clothes before driving off), so the lack of contamination is a serious problem in the case against Ivins as sole suspect. Dr. CJ Peters was asked about this issue, and confirmed this point in an August 20 article here.