Try these;
http://www.truthout.org/docs_02/08.15C.kristof.anthrax.htm
http://www.amazon.com/exec/obidos/tg/detail/-/006052278X/104-5564700-2462367?v=glance
http://www.angelfire.com/ex/projecthatfill/seed.html
There was also a program on the history channel that discussed Hatfield's crusading nature on the subject of bio-terrorism and what he felt was the governments unpreparedness for an attack, among other things.
The fact that some of the anthrax envelopes contained warnings to take penicillin and warned that the envelope contained anthrax shows that the sender didn't intend to actually kill anyone, rather scare the government into greater awareness of bio-terror.
Many people in the bio-warfair field consider Hatfield the prime suspect. That is not to say it couldn't have been someone else, just that Hatfield seems far and away, most likely.
For Piasa. Most investigators and bio-warfair insiders think he did it. There are too many coincidences. The more you look into it the more convinced you will be too. His defenders are politically motivated. They gloss over things like his pathological lying by claiming he is just a big kidder.