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A co-worker, Dr. W. Russell Byrne, who worked in the bacteriology division at Fort Detrick, told reporters that Mr. Ivins had been “hounded” by FBI agents who raided his home twice and had been removed forcefully from his job by local police over fears that he had become a danger to himself or others.

Dr. Byrne said the ongoing investigation led last month to Mr. Ivins’ hospitalization for depression. He said he did not believe that Mr. Ivins was involved in the anthrax attacks.

Sen. Charles E. Grassley, Iowa Republican and one among a number of members of Congress who had serious questions about the anthrax investigation, said Friday he was “looking forward to getting more detailed information about these reports directly from the FBI and other sources.

“It’s been frustrating that the FBI has essentially shut out Congress throughout its seven-year investigation. Now seems to be the opportune time for the bureau to brief Congress about whether the case is to be closed and justice will be served,” Mr. Grassley said.

“If it is, we must thoroughly examine the reasons why,” he said. “In the meantime, we should remember that a rush to judgment can be dangerous and expensive for everyone. The last person the FBI had in its sights in this case suffered for six years and just collected a $6 million settlement”

In December 2006 letter, 33 members of Congress described as “inappropriate” a decision by the FBI to refuse congressional requests for information on the investigation and criticized the bureau for a blanket prohibition on anthrax briefings because of concerns over the potential disclosure of sensitive information.

Mr. Grassley said at the time that the FBI was seeking to “thwart the constitutional responsibility of Congress” and that the bureau’s refusal to provide briefings to Congress following the 2001 anthrax attacks appeared to be “the rule rather than the exception.”

Rep. Rush D. Holt, New Jersey Democrat who was at the forefront of efforts to get information on the anthrax probe, said the attacks had harmed the “heath and livelihoods of my constituents and paralyzed the government and national commerce.” He said Americans deserved to know why the investigation “had made so little progress.”

Tom LoBianco contributed to this article.