I have no theory.
I think we can agree that experts qualified to say whether a BL-3 versus BL-4 is required (or some other means) include Patrick, Alibek and Ezzell.
Dr. Patrick thought the FBI’s theory about loading the envelopes in ponds was stupid — because of the moisture problem. Drying is the key to making a good product. My military scientist says the FBI has underestimated the importance of drying skill in the process.