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.