A few short days after the Johnston/Broad article, the FBI narrowed its investigation to microbiologist Steven J. Hatfill. Through leaks to various news organizations, Hatfill’s involvement in research programs at Ft. Detrick appeared in numerous media. Camera crews were on hand to film the FBI hauling things away from Hatfill’s apartment near Ft. Detrick.

Stories revealed that Hatfill had been terminated from a research project at Ft. Detrick in August 2001. Hatfill says he was fired because of publicity about him being a possible suspect in the anthrax mailings. Other stories say his (top secret) security clearance either expired or was revoked for unknown reasons. (This, of course, would give a "revenge" motive, another part of the FBI "profile".)

Hatfill participated with William Patrick (said to be his mentor) in a 1999 study of the consequences of mailing anthrax. Some believe that study may have been the template for the anthrax mailings closely following the 9/11 terrorist attacks.

However the study was flawed in two respects. It did not contemplate the use of the "new" one trillion-spore concentration whose diameter is smaller than the pores in the average envelope. Nor did it take into account the pressure exerted by mail sorting machines.