There was a lead FBI investigator who referred to letters and trays as "boxes". Another lead FBI investigator actually told members of the media (who were equally ignorant) that he/she had no idea how anthrax could be spread through the mail unless there were more letters.
Stupidity like that - if not that very stupidity - killed two people in the Postal Service and allowed many others to be infected, and hundreds to be exposed.
CDC people actually thought anthrax particles as small as 1 to 5 microns couldn't migrate through paper envelopes. It turned out those envelopes have holes 100 microns in size. CDC people were also saying you had to breathe a minimum of 18,000 spores to develop inhalation anthrax. Later on they revised this number all the way down to 1 spore.
Postal managers were rightly criticized for having no contingency plan in case of an anthrax attack that infected postal equipment; on the other hand, both the CDC and the FBI had never examined that problem themselves, and when confronted with the reality, denied that it was at all a problem - except to Senator Daschle who was acting all so brave over it.
Lots and lots of bureaucrats in Washington should be sacked and replaced. Let's start with the CDC guys, then the FBI, and work our way through the Postal Service - but only after we get a few idiots suspended from the US Senate!
Doesn't this make it likely there are at least two individuals involved? Once you get two, doesn't it seem likely there are a bunch?