WASHINGTON—Answers to one of the nation’s most high-profile unsolved mysteries are in documents that could be released as early as this week—and help explain how the government chased the wrong suspect for years.

Prosecutors were mulling this weekend whether to close the investigation early this week, possibly as early as Monday or Tuesday. If that happens, court documents detailing newly developed scientific evidence that recently led the government to Bruce E. Ivins may be unsealed.

Five people died and 17 others were sickened when anthrax-laced letters began showing up at congressional offices, newsrooms and post offices soon after Sept. 11, 2001.

After wrongly investigating Army scientist Steven Hatfill, the FBI more than a year ago began looking at Ivins, who worked at the same military lab. Ivins, a decorated scientist who was working on an anthrax cure, killed himself last Tuesday.

Two U.S. officials said victims and their survivors could be briefed as early as Tuesday on the final piece of the bioterrorism attacks that confounded the government.

The Justice Department attributed the break in the case to “new and sophisticated scientific tools” that cost the FBI about $10 million. Investigators said the science focused, in part, on how the anthrax strains were handled and who had access to it at the time of the mailings.

FBI scientists were able to isolate strains used in the attacks, and determined they were not as common as previously thought. And that led investigators to Ivins.

Had the same process been available years ago, it would have cleared Hatfill much earlier, according to two people familiar with the FBI investigation who spoke on condition of anonymity because the case is not officially closed.

David R. Franz, a former commander of the Army’s lab biological warfare labs at Fort Detrick, Md., where Ivins worked, said Saturday he thought it was “very important that the FBI present their case against Bruce and not just state that the investigation was over because it was him and he’s gone.”

Franz added, “I’m concerned about what closing this case without conclusive evidence might do to harm our life sciences enterprise. ... I think we as Americans need to see the proof.”

Initially, FBI profilers said they probably were looking for a loner with a scientific background. Maybe he had a grudge against the lawmakers and news organizations. Investigators also considered possible links to al-Qaida, the terrorist group behind the 9/11 attacks.

Intensive focus initially settled on Hatfill, who for years accused the government of unfairly targeting him. In late June, the government exonerated Hatfill and paid him a $5.82 million settlement.

With that, the government seemed no closer to solving the “Amerithrax” mystery. But, quietly, investigators were closing in on a different scientist, Ivins.

A murder indictment and the possibility of the death penalty could have produced a high-profile climax to the case. Shadowed by the FBI, Ivins died Tuesday from a Tylenol overdose, leaving the probe in limbo and a nation seeking answers.

“It’s a shame the man is not here with us. We might have known more,” said Maureen Stevens, whose husband, Bob, was the first anthrax victim.

Former Senate Democratic leader Tom Daschle of South Dakota, said: “I think the FBI owes us a complete accounting of their investigation and ought to be able to tell us at some point, how we’re going to bring this to closure.” Daschle’s office received a letter containing the deadly white powder in 2001.

Among the unanswered questions is why the anthrax was sent. The FBI was investigating whether Ivins, renowned for his work developing anthrax vaccines and treatment, released the toxin to test those cures. Ivins was one of several scientists named in an application for a vaccine patent 18 months before the attacks.

Another puzzle is what finally led the FBI to focus on Ivins a year or so ago. Ivins attracted some attention for conducting unauthorized anthrax testing in the six months following the anthrax mailings, but the FBI focus stayed on Hatfill.

As Ivins’ name emerged, so did a portrait of a conflicted, troubled man. His friends knew him as the man who played the keyboard at church, a Red Cross volunteer who was an avid juggler and gardener.

Others saw a darker side. Police recently removed him from work, fearing he was a danger to himself or others. Social worker Jean C. Duley filed for a restraining order in a Maryland court.

“Client has a history dating to his graduate days of homicidal threats, plans and actions towards therapists,” Duley wrote in court documents last week, adding that his psychiatrist had described him as homicidal and sociopathic.

Ivins’ brother, Tom Ivins, said he had not spoken to Bruce Ivins since 1985, but acknowledged the possibility his brother may have been the anthrax mailer.

“It makes sense, what the social worker said,” Tom Ivins said. “He considered himself like a god.”

Ivins’ lawyer, Paul F. Kemp, asserted the scientist’s innocence and said he would have proved it at trial. Kemp said his client’s death was the result of the government’s “relentless pressure of accusation and innuendo.”

Maryland’s chief medical examiner, Dr. David Fowler, confirmed Saturday that Ivins died Tuesday morning at Frederick, Md., Memorial Hospital; that the cause of death was found to be an overdose of acetaminophen, the active drug in Tylenol; and that it was ruled a suicide based on information from police and doctors.