The Justice Department on Tuesday revealed details of its anthrax (search) investigation to a federal judge who is considering a lawsuit brought by a scientist described as a "person of interest" in the case.

The information from Richard L. Lambert (search), the FBI's lead investigator in the October 2001 anthrax attacks, was provided to U.S. District Judge Reggie B. Walton (search). After the judge reviewed the document it was returned to the Justice Department and locked in a vault.

Walton is expected to decide soon whether to throw out parts of the lawsuit filed by Dr. Steven Hatfill (search) against Attorney General John Ashcroft (search) and others. Hatfill said his reputation was ruined when Ashcroft labeled him a "person of interest" in the anthrax attacks, which killed five people and sickened 17.

Hatfill has denied any wrongdoing.

A department spokesman declined to describe what details Lambert gave to the judge, noting the document was classified. The information was not given to defense lawyers for Hatfill.

Hatfill's lawyers, Tom Connolly and Mark Grannis, declined to comment.

The FBI considers the anthrax investigation its most complex ever. Letters laced with anthrax that were mailed to government and news media offices, including to Sens. Tom Daschle, D-S.D., and Patrick Leahy, D-Vt., and to The New York Post and NBC anchor Tom Brokaw. No one was charged.

Hatfill is a former government scientist and bioweapons expert who once worked at the Army Medical Research Institute of Infectious Diseases at Fort Detrick, Md. The facility housed the strain of anthrax found in the envelopes sent to the victims, though Hatfill maintains he never worked with the bacterium, bacillus anthracis, that causes the infectious disease.

FBI Director Robert Mueller has said the investigation, dubbed "Amerithrax," is focused on scientific tests to learn how the anthrax was made and who might have been capable of making it.

Walton previously decided to delay Hatfill's civil lawsuit until at least October. That decision came after Lambert told him a delay was "critical to the integrity and successful resolution" of the anthrax investigation. He warned that Hatfill probably will seek copies of sensitive internal FBI documents that would reveal names of people cooperating with investigators and other closely held details about evidence that has been collected.

Disclosing such information would provide "a voyeur's window" into the investigation, Lambert said, and give Hatfill or others ideas about destroying or hiding evidence, retaliating against witnesses or fleeing the country.

Hatfill's lawyers have described the government's assertions as a "parade of horribles" and said the information sought would not jeopardize the investigation.