It's the FBI's third search of Hatfill's Frederick, Md., apartment; they also polygraphed him months ago and combed through his storage space in Ocala, Fla., a month ago. This time, it's not anthrax spores they're looking for, but the FBI isn't saying much more, reports CBS News Correspondent Sharyl Attkisson.
"We are making progress in the case, but beyond that I can't comment on the ongoing activities of the investigation," said FBI Director Robert Mueller.
Hatfill, 48, was not questioned and no arrests in the case are imminent, a government official said.
Officials won't say what triggered the intensified interest in Hatfill. Though they're careful not to call him a "suspect," there's no question he's becoming an increasingly important figure in the investigation.
Federal investigators first searched Hatfill's home on June 25 and questioned him about last year's deadly anthrax mailings. During the search, FBI agents, some in protective clothing, removed computer components and at least a half-dozen garbage bags full of material from Hatfill's apartment.
But officials said no trace of anthrax was found in his home or at the storage unit he rented in Florida.
On Thursday agents searched Hatfill's apartment and the trash bins outside the building. A dark blue van was parked nearby with its back doors open and white cardboard boxes sat next to the bins.
Hatfill keeps a residence at the apartment building, but has not lived there since the first search, according to neighbors.
The apartment is a stone's throw from Fort Detrick, where Hatfill worked for two years for the Army Medical Research Institute of Infectious Diseases, center of the nation's biological warfare defense research.
While there he, like other scientists, had access to the strain of anthrax used in the post-Sept. 11 mail attacks. He's believed to have been vaccinated against the deadly anthrax.
He also caught investigators' attention because he once commissioned a study that mentioned an anthrax-laced envelope being opened in an office. Also, the fictitious return address on the letters used in the anthrax attacks was "Greendale School" and Hatfill once studied in Zimbabwe near a school called Greendale.
Hatfill is also said to have lost his government security clearance shortly before the attacks.
The FBI has identified Hatfill as one of 20 to 30 scientists and researchers with the expertise and opportunity to conduct the anthrax attacks, but investigators say he is not a suspect.
The bureau has searched about 25 homes or apartments after getting permission from the person interviewed, a federal law enforcement official said.
Hatfill has not spoken publicly about the searches. In March,
however, he denied involvement in the anthrax mailings and complained to The (Baltimore) Sun in a telephone message that he was fired from a recent job because of media inquiries.
"I've been in this field for a number of years, working until 3 o'clock in the morning, trying to counter this type of weapon of mass destruction, and, sir, my career is over at this time," Hatfill said.
Hatfill and another scientist, Joseph Soukup, commissioned a study of a hypothetical anthrax attack in February 1999 as employees of defense contractor Science Applications International Corp., said Ben Haddad, spokesman for the San Diego-based company.
Five people died from inhaling anthrax spores mailed last fall.