As the FBI began draining an entire pond today in its 20-month-old anthrax probe, investigators remained focused on one man in the hunt for the perpetrator, ABCNEWS' World News Tonight reported.
And today's unusual move appears to be the FBI's last, best shot at proving what it so far has been unable to prove, that former government scientist Steven Hatfill was the anthrax killer.
Five people died and more than a dozen others were sickened in the rash of anthrax attacks targeting Congress and media outlets in the fall of 2001.
The decision to drain the pond in Maryland's Frederick Municipal Forest was based on what federal officials say is no more than a growing circumstantial case against Hatfill, federal law enforcement sources said.
The FBI's working theory, sources said, is that Hatfill, who lived eight miles away in Frederick, Md., next to U.S. Army Medical Research Institute of Infectious Diseases where he worked, used makeshift lab equipment to put finely powdered anthrax in envelopes, and then dumped the equipment in the pond.
Hatfill has vehemently denied any involvement in the anthrax attacks, and his spokesman reiterated that today.
"They can drain the Pacific Ocean and they're not going to find any evidence that Steve Hatfill was the anthrax killer because he's had no involvement whatsoever," said Hatfill spokesman Pat Clawson.
The Sweater Box Mystery
But the circumstantial case is continuing to develop. The FBI was led to the pond last year by bloodhounds, including one named Tinkerbell, tracking the scent picked up from Hatfill and the anthrax letters, federal sources said.
Over the Christmas holiday, FBI divers recovered what they think was a piece of the makeshift equipment used to load the anthrax, a plastic sweater box with two hand-sized holes cut in it, sources said.
Other circumstantial evidence that has sources said has led the FBI to continue its focus on Hatfill includes his presence in Florida, around the time an anthrax-laced letter was mailed to the American Media Co. in Boca Raton, Fla.
Also, sources said, Hatfill made an admission to the FBI that he was taking the powerful antibiotic Cipro at the time of the anthrax attacks, which he reportedly said was for a nasal infection.
Cipro is the treatment prescribed for suspected anthrax poinsoning, and was given preventatively to thousands of people at the peak of the anthrax attacks.
Still, none of that circumstantial evidence has produced an arrest, leaving the FBI draining a 1-acre pond, a process that is expected to take three to four weeks and cost $250,000.
"If the FBI had any facts tying Steve Hatfill directly into the anthrax case, I don't think he'd be out walking the streets right now," said Clawson.