Researcher Meryl Nass quotes CBS:
It is unclear how the FBI eliminated as suspects others in the lab who had access to the anthrax. It's not clear what, if any, evidence bolsters the theory that the attacks may have been a twisted effort to test a cure for the toxin. Investigators also can't place Ivins in Princeton, New Jersey, when the letters were mailed from a mailbox there.
If I have time, I'll wander over to the document dump at the DOJ and see if it looks convincing. I have an open mind on this, but after Hatfill I think we should all consider the evidence carefully.