Bio-weapons researcher Dr. Steven Hatfill, sources confirm, remains the FBI's number one suspect in the attacks, even though round-the-clock surveillance and extensive searches have failed to develop more than what sources describe as a "highly circumstantial" case.
"I am not the anthrax killer," said Hatfill, denying the accusations.
And now one possible outcome, sources suggest, is that the government might take the unusual step of bringing charges against Hatfill unrelated to the anthrax attacks at all, if they become convinced that's the only way to prevent future incidents.
Not unlike, for example, the income tax evasion charges finally brought against Al Capone, when evidence of racketeering proved elusive.
Hatfill and his attorneys are aware of this possibility. They say they have always offered their full cooperation to the FBI, but declined to comment.
Van Harp is the senior FBI official in charge of the case. He's retiring this week and he also declined to talk specifics.
"I think we've made progress," said Harp of the anthrax case. "It's frustrating that it took so long. I think everyone involved in the investigation is frustrated over it."
Much of that frustration, investigators admit, has been the sheer volume of the science involved in not only identifying the strain of anthrax used, but then reverse engineering it and breaking down its DNA.
"We just can't hurry the science, nor would we want to. And we're making sure whatever the results are, that it's admissible," said Harp.
Admissible in the event, that is, that anyone is ever actually charged with the crimes.