A federal judge is prodding lawyers for a scientist investigated in connection with the anthrax attacks in 2001, Steven Hatfill, to escalate a battle with the press by insisting that reporters identify anonymous government sources who linked Mr. Hatfill to the probe.

Judge Reggie Walton issued an order last week warning Mr. Hatfill that he may lose his civil lawsuit over the leaks if he does not compel journalists to name their sources. “A wealth of case law suggests that in order to prove that a violation of the Privacy Act has occurred, the actual source of the information must be identified,” the judge wrote. “Whether the plaintiff can satisfy this requirement with circumstantial evidence alone is an endeavor the plaintiff assumes at his peril if he decides to not further identify the source or sources of the purported improper disclosures.”

Mr. Hatfill’s legal team has taken depositions from journalists at ABC, CBS, Newsweek, and the Washington Post. The scientist’s lawyers thought they had averted a First Amendment clash by crafting a deal under which the reporters withheld the names of their sources but divulged their affiliation with the FBI or Justice Department.

However, at a hearing on March 19, Judge Walton signaled that probably would not be good enough. “I understand the concerns the plaintiff has with compelling the press, but my inclination is that that’s going to have to be done,” the judge said, according to Legal Times.

Judge Walton, who recently saw several high-profile journalists on the witness stand as he oversaw the trial of I. Lewis Libby Jr., gave Mr. Hatfill until April 16 to decide whether to press the press to give up its sources. An attorney for Mr. Hatfill, Thomas Connolly, did not return a call seeking comment for this article.

Neither Mr. Hatfill nor anyone else has been charged with producing the anthrax-laden mailings, which are believed to have killed at least five people.