One of the nation's top biodefense researchers has apparently taken his own life, just as the FBI zeroed in on him as a suspect in the deadly 2001 anthrax attacks.
Sources familiar with the investigation tell ABC News that 62-year-old Bruce E. Ivins, who worked at the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID) at Fort Detrick, Md., died at a Maryland hospital Tuesday of a prescription drug overdose. The story of the Ivins investigation was first reported by the Los Angeles Times.
A source familiar with the investigation told ABC News that the government did not officially notify Ivins that he was a target of the investigation or that he was close to being indicted.
Ivins' attorneys learned of the government's intent to move forward with the prosecution of their client after he died on Tuesday, but had suspected the case was headed in that direction based on investigators' focus on the scientist, the source said.
Ivins' death came as FBI agents had been aggressively interviewing friends, family and associates about the possibility he was responsible for a series of anthrax mailings in the fall of 2001 that left five dead, sickened 17 and terrorized a nation still reeling from the Sept. 11 attacks.
The Justice Department released a statement on the anthrax investigation Friday, noting that there have been "significant developments" in the joint DOJ, FBI and U.S. Postal Inspection Service probe, but declining to go into detail.
Though they were "able to confirm that substantial progress has been made in the investigation by bringing to bear new and sophisticated scientific tools," the statement added that the investigative agencies "have significant obligations to the victims of these attacks and their families that must be fulfilled before any additional information on the investigation can be made public."
Additionally, investigative documents in the case remain under seal, but the statement said investigators "anticipate being able to provide additional details in the near future."
"I think it's incredibly disheartening that we as victims and survivors will never be able to sit in a courtroom with this man -- if indeed he was the person responsible -- and face him, and share with him how he so dramatically traumatized us and forever changed our lives," victim Casey Chamberlain, a former executive assistant at NBC News, said in a statement.
"I will never stop thinking about this case as long as I live."
Ivins had actually helped the FBI in the anthrax investigation and had ties to the location in New Jersey where the anthrax was mailed. The toxin arrived via mail to Capitol Hill offices and at news organizations in Florida and New York.
In a statement released Friday morning, Ivins' attorneys, led by Paul F. Kemp, asserted his late client's innocence and said they are "disappointed that we will not have the opportunity to defend his good name and reputation in a court of law."
Ivins had cooperated with investigators and appeared before the grand jury "many times," but had consistently maintained his innocence, the source familiar with the investigation told ABC News. His defense team had noticed Ivins was under increasing strain as a result of the investigation, and there was concern about how he was handling the news, the source said.
The source described the investigation as a "circumstantial case," with no direct evidence against Ivins, who was one of at least 30 people who had access to the anthrax at various times. FBI officials had long targeted Fort Detrick as the possible source of the anthrax attacks because of the facility's intensive research on anthrax as a biological weapon, but some seemed skeptical of the case against their colleague.
One official went as far as to call the FBI's actions "irresponsible" and said of Ivins, "He was a nice guy. He did his work and kept to himself."
"The USAMRIID family mourns the loss of Dr. Bruce Ivins, who served the Institute for more than 35 years as a civilian microbiologist," read the official statement from Fort Detrick.
The statement also made mention of the fact that in 2003, Ivins received the highest possible civilian honor from the Defense Department, the Decoration for Exceptional Civilian Service. "We will miss him very much," it ended.
Investigators obtained warrants to search the Ivins home twice, and they had taken a sample of his DNA, the source said.
"For six years, Dr. Ivins fully cooperated with that investigation, assisting the government in every way that was asked of him," Kemp's statement said.
Noting his years of service as a military scientist, Kemp added, "The relentless pressure of accusation and innuendo takes its toll in different ways on different people, as has already been seen in this investigation. In Dr. Ivins' case, it led to his untimely death."
Even before his death, court records obtained by ABC News from the District Court of Maryland for Frederick County paint a picture of a man who had recently been displaying the effects of that pressure.
A social worker named Jean Duley had filed a protection order against Ivins last month, alleging that he had made "threats of homicidal intent" in mid-July. The court documents also indicate that Ivins had been admitted to a hospital in the area and was under psychiatric care.
"Client has a history dating to his graduate days of homicidal threats, actions, plans threats & actions toward therapist [sic]. Dr. David Irwin his psychiatrist called him homicidal, sociopathic, with clear intentions," a handwritten page submitted with the application stated.
"Will testify with other details FBI involved, currently under investigation & will be charged w/ 5 capital murders. I have been subpoena [sic] to testify before a federal grand jury August 1, 2008 in Washington, D.C."
A judge granted the petition, ordering Ivins stay away from Duley's home, work and not to contact her, but the court officially dismissed the case Thursday because of Ivins' death.
According to the source familiar with the case, a police officer filled out the paperwork not to secure the order, but rather to get an emergency evaluation for Ivins. Duley, who worked in Ivins' psychiatrist's office, recounted what Ivins said in the course of therapy to the officer, the source said.
ABC News attempted to speak to Duley at her Williamsport, Md., home Friday, but a man who answered the door would not identify himself, confirm that Duley lives at the residence or comment on the information contained in the court documents.
Earlier Friday afternoon, policemen responded to the Ivins residence in Frederick -- just across the street from Fort Detrick -- to speak to Ivins' widow, Diane, about a complaint she had called in about the media presence outside her home.
Dozens of reporters and camera crews lined the street outside the small two-story home with dark red shutters and white plastic siding.
Diane Ivins has not spoken to the media gathered outside her home. "While understanding the job that you guys have to do, she just doesn't want to be bothered," Frederick Police Department Det. Sgt. Bruce DeGrange said after he spoke to her.
"She seemed fine," he added. "She's a little upset about the attention, but she seems fine."
In regards to the anthrax case, which has frustrated government investigators for years, FBI Director Robert Mueller said in a recent interview with ABC News that he was confident the case would be solved.
"We've made progress in the investigation -- I'm comfortable that the investigation is on course and that ultimately it will be successful," Mueller said.
But there have been major missteps in this case, and the FBI has thought it was close before.
In June, the government settled a lawsuit with another scientist from Fort Detrick, agreeing to pay Steven Hatfill nearly $6 million amid allegations he was unfairly targeted and humiliated by leaks to the press. In August 2002, then-U.S. Attorney General John Aschcroft named Hatfill as a person of interest in the mysterious mail attacks, but he has never been charged in connection with the case.
As for the ongoing investigation into the attacks, the anthrax task force is currently comprised of 17 FBI special agents and 10 U.S. Postal Service inspectors. As part of the probe, known as "Amerithrax," investigators have "executed approximately 75 searches and conducted more than 9,100 interviews in the relentless pursuit of the perpetrator of these attacks," according to the Justice Department.
The bureau has not commented extensively on the investigation, but in the fall of 2006, FBI scientist Doug Beecher, a member of the bureau's Hazardous Materials Response Unit based at the its laboratory at Quantico, Va., wrote in an article that no specialized equipment or specialized knowledge of bioengineering was needed to pull off the 2001 attacks.
Beecher's article, which appeared in the journal Applied and Environmental Microbiology, is a rare example of the FBI disclosing information on the anthrax investigation.
According to Homeland Security officials, President Bush occasionally asks how the investigation is proceeding during his morning intelligence briefing.
ABC News' Jason Ryan contributed to this report.