Note that one of the lines was "We have this anthrax." Not "I have this anthrax", some anthrax . . . having used 1st person plural rather than lst person singular as one would expect a loner to do.
I'm sure they are looking into every aspect of the Vietnamese woman's life, including how she came to be on the Embassy roof in Saigon when it was evacuated.
I read that she paid her bills by money order. I would think that when money orders are obtained in bulk and distributed to different outlets, such as convenience stores, there ought to be some sort of serial numbers on them, and some sort of accounting procedure, even crude, for where each batch went for sale. Surely they have looked into this angle as well.