CLUE?
So, I contacted FBI through the internet website set up to collect such information AND I talked to several different Postal Inspectors about the matter, and included written material.
What that meant was the individual who addressed the anthrax letters in a rather peculiar format actually looked at that publication as his guide.
Believe it or not the three addresses recovered were in an absolutely unique structure ~ so once you find the publication (not sold on news stands) you simply go to the publisher and find the distribution list.
You then match that distribution list against persons with some professional relationship with anthrax (production or research) and you know where to start.
FBI's approach took them an additional 7 years to get to Dr. Ivins. My clue, if even looked at, would have cut that 7 years out of the process to get them to the same dead end, but 7 years earlier!
At that time witnesses memories would have been fresher, custody records more complete, casual conversations with other potential targets still remembered, etc.
Since I am sure the FBI has not yet gotten the perp I can hold out for getting the reward once they make an arrest. There are at least 2 other FREEPERS who have targeted others who may well have had access to the exact same anthrax source when it had the 4 mutations they believed they found.
I don't believe FBI thinks they've solved the case.