Secrets are being kept.
Personally, I think there are at least three distinct possibilities ~ one of them is that the same people who attacked the USPS back in the 1970s shortly after the abortive Bulk and Foreign Facility strike in New Jersey. Their friends are among those who target Hatfill.
Another is that the Atta gang did it, and there are reports of some of them having anthrax infections.
Another is that the group associated with the Blind Sheikh (in jail for his part in the first WTC attack) did it ~ and that includes a former postal employee who worked in Staten Island.
Read link I posted above, it has been publically announced that they were not strains used foreign governments based on the anti-caking agents. Now think for a moment-- If it were US labs what would you see? No report in the news because that would almost certainly be classified for a number of reasons, but the FBI would know for sure and we would see a focus on USAMRID. They did, screening every scientist who had custody or knowledge of the process. Read between the lines.
As a group those are certainly suspicious characters. ;)