The FBI appears to have run out of leads in their search for the anthrax killer(s):
Md. Pond Produces No Anthrax Microbes
FBI Sought Clues In Deadly Attacks
The Washington Post
Lab tests of soil samples taken from a Frederick pond that the FBI drained in June have shown no traces of anthrax bacteria, law enforcement sources said, a disappointment to authorities who were hoping the high-stakes gamble would pay off.
...
With the latest excursion in the Frederick Municipal Forest leading to a dead end, investigators are continuing to work with scientists to genetically code the anthrax bacteria in hopes of tracing it to a particular lab, law enforcement sources said.
Investigators also are retracing some steps in the probe and re-interviewing people, a common investigative technique used in hard-to-crack cases in need of fresh leads.
http://www.washingtonpost.com/wp-dyn/articles/A10591-2003Jul31.html