WASHINGTON (CNN) -- Federal investigators will declare the 2001 anthrax case solved on Wednesday, when they make public their case against government researcher Bruce Ivins, a government source familiar with the case told CNN on Tuesday.
But the case will not be considered closed, because administrative details remain incomplete, said the source, who spoke on condition of anonymity because the investigation is ongoing.
Before making the information public, the FBI is expected to share the evidence of Ivins' involvement with survivors and relatives of victims in the anthrax attacks, the source said.
A lawyer for Maureen Stevens, the widow of Bob Stevens, the first victim of the 2001 attacks, said she was invited to the session and will attend.
The tabloid photo editor died after inhaling anthrax that investigators believe was in a letter sent to American Media Inc., the publisher of the Sun and National Enquirer tabloids, at its offices in Boca Raton, Florida.
Another source familiar with the investigation said Tuesday that in the fall of 2001, Ivins borrowed a machine that can convert wet anthrax, the kind used at Fort Detrick, into dry powder, which was found in the anthrax letters.
Such machines, called lyophilizers, are not usually used at Fort Detrick, where Ivins worked, though they are easy to obtain.
Experts said the report may have no significance.
"I wouldn't necessarily make the conclusion that, just because he had access to a lyophilizer and used a lyophilizer, that that provides a smoking gun, that he must be using this for sinister purposes," said Peter Hotez, chairman of microbiology at George Washington University in Washington.
Richard Spertzel, a former biodefense scientist who worked with Ivins at the lab at Fort Detrick, said there was "no way" a lyophilizer could have created the fine anthrax spores used in the 2001 letters.
Spertzel said a more advanced machine would have been needed, and that no one working at a U.S. government lab could have produced such high quality anthrax in secret.
Ivins, who is expected to be blamed for the mailings of the toxin, which killed five people and sickened more than a dozen others -- died July 27 at a hospital in Frederick, Maryland, from an apparent suicide attempt two days earlier.
No charges have been made public.
He became a suspect after investigators found DNA evidence from the 2001 anthrax mailings on a flask used in his laboratory at the U.S. Army Medical Institute of Infectious Diseases, said a source who is familiar with the investigation but not authorized to speak publicly about the case.
Ivins had worked for decades in the biodefense lab at Fort Detrick, where he was trying to develop a better vaccine against the toxin.
The FBI had traced the anthrax used in the attacks to the lab by using a new technology, a U.S. official familiar with the investigation said.
Authorities were looking at whether Ivins may have released anthrax to test a vaccine he was working on, another official said.
Some of the anthrax-laced letters, written in crude block letters, included the words, "Take penacilin (sic) now," according to photographs released by the FBI.
Since Ivins' death, suspicions about his involvement in the anthrax attacks have surfaced alongside questions about his sanity.
At the time of his death, the 62-year-old scientist was under a temporary restraining order sought by a social worker who had counseled him in private and group sessions. She accused him of having harassed, stalked and threatened her with violence.
The woman told the court in her complaint that Ivins had been treated at a mental health facility.
Steven Hatfill, another government scientist who was named by the Justice Department as a "person of interest" in the attacks, was never charged. He sued the department, which settled the case in June.
The skepticism in scientific circles about the strength of the case against Ivins heightens the importance of the government's unveiling of its evidence against the scientist, a former prosecutor said.
"I think the public and the survivors of the anthrax attacks are entitled to see the evidence before the grand jury," said Andrew McBride. "And if there was a draft indictment and they were ready to indict Mr. Ivins, they ought to see that as well."
CNN Producer Kevin Bohn contributed to this story.