Washington ? FBI and Postal Service agents wearing protective gloves conducted a second search Thursday at the apartment of a former Army researcher considered a “person of interest” in the investigation of last year’s deadly anthrax mailings.

The FBI gained a search warrant to look inside Steven J. Hatfill’s residence at Detrick Plaza Apartments in Frederick, Md., according to two U.S. government officials who spoke on condition of anonymity.

Hatfill consented to the first FBI search on June 25 and no warrant was needed.

Federal agents also searched trash bins outside Hatfill’s apartment and a self-storage unit in Ocala, Fla., that Hatfill used, one official said. The unit also was searched in June.

It was unclear whether the FBI contacted Hatfill before gaining the warrant to search his home.

FBI Director Robert Mueller declined to say why a second search was conducted.

“We’re making progress in the case, but I can’t comment on ongoing aspects of the investigation,” he said.

Hatfill, 48, was not questioned and no arrests in the case are imminent, a government official said. Hatfill is not a suspect and no physical evidence links him to the letters, law enforcement officials said.

Five people were killed in last fall’s anthrax mailings. Federal investigators did talk to Hatfill about the case when his name first surfaced last winter, but no details of the interview have been disclosed.

During the first search, FBI agents, some in protective clothing, removed computer components and at least a half-dozen garbage bags full of materials from Hatfill’s apartment.

But officials said no trace of anthrax was found in his home or at the storage unit.

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 he has not lived there since the first search, neighbors said.

The apartment complex is outside 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.

Hatfill worked at the facility until September 1999. Although he probably had access to anthrax, his primary duties didn’t involve working with it, a spokesman for the base has 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.

The FBI has identified Hatfill as one of 20 to 30 scientists and researchers with the expertise and opportunity to conduct the anthrax attacks. The bureau has searched about 25 homes or apartments after getting permission from the person interviewed, a federal law enforcement official said.