WASHINGTON (CNN) -- An anthrax researcher who committed suicide Tuesday had threatened his therapist and recently outlined a plan to kill his co-workers, according to audiotape of court testimony.
Biodefense researcher Bruce E. Ivins, seen here in 2003, died from an apparent suicide Tuesday.
Therapist Jean C. Duley testified on July 24 that Bruce E. Ivins described a "detailed homicidal plan" to kill his co-workers after learning he was going to be indicted on capital murder charges.
Sources told CNN that prosecutors might have sought the death penalty against Ivins, who killed himself after learning he was going to be charged in the 2001 anthrax mailings.
Five people died and dozens more became ill after letters containing the anthrax bacteria were sent to congressional offices and media organizations soon after the September 11, 2001, terrorist attacks.
Duley testified that Ivins had been diagnosed as a "sociopathic, homicidal killer" by several top psychiatrists.
During a recent group therapy session, Ivins said he had bought a bullet-proof vest and obtained a gun after learning of the pending charges, Duley said.
"He was going to go out in a blaze of glory," testified Duley, who said that Ivins also threatened her.
Frederick County District Judge W. Milnor Roberts issued a temporary protective order on July 24, ordering Ivins to not to contact Duley and to stay away from her workplace.
He was due in court Thursday.
Two sources familiar with the investigation said that on Tuesday, the day Ivins died, lawyers were to meet and discuss a possible plea deal for him. Watch a report on the researcher and the investigation »
The meeting took place between prosecutors and a defense attorney even after authorities learned of Ivins' death, one of the sources told CNN on Saturday.
It is not known what was discussed. But sources said some of the government's key scientific evidence was going to be shown to Ivins' attorney at the meeting, which had been scheduled for some time.
Neither the Justice Department nor defense lawyer Paul Kemp would comment.
On Friday, sources told CNN that prosecutors might have sought the death penalty for Ivins' role in the anthrax mailings. They could not confirm a report published Saturday in The Washington Post that part of the proposed deal would take the death penalty off the table.
Ivins worked for decades in the U.S. Army Medical Institute of Infectious Diseases' biodefense lab at Fort Detrick, Maryland. He was trying to develop a stronger vaccine against the deadly anthrax toxin.
The FBI had traced the anthrax used in the attacks to the lab using a new genetic technology, a U.S. official familiar with the investigation said.
The Ames strain of the anthrax spore that was used in the 2001 attacks was commonly used in U.S. government labs. Scientists said creating a "weapons grade" form of anthrax is a complex process requiring extensive professional expertise.
Authorities were looking at whether Ivins may have released anthrax as a way to test a vaccine he was working on, another official said.
Kemp, who said his firm had represented him for more than a year, said he was disappointed that Ivins "will not have the opportunity to defend his good name."
"For six years, Dr. Ivins fully cooperated with that investigation, assisting the government in every way that was asked of him," Kemp said.
Kemp said Ivins was innocent and blamed his death on the investigation.
"The relentless pressure of accusation and innuendo takes its toll in different ways on different people, as has already been seen in this investigation," Kemp said. "In Dr. Ivins' case, it led to his untimely death."
Early in the investigation, then-Attorney General John Ashcroft publicly identified former civilian anthrax researcher Steven Hatfill as a "person of interest" in the investigation.
Hatfill, who also worked at the biodefense lab at Fort Detrick, denied involvement and sued the Justice Department for violating his privacy by leaking his name to the media in connection with the investigation.
The department settled in June with Hatfill, who is to receive a one-time payment of $2.8 million and $150,000 a year for life.
Other scientists who worked at government laboratories said they, too, came under unwarranted suspicion.
The FBI had at least two dozen agents working the case as of two years ago, conducting more than 9,000 interviews, but investigators told CNN in 2006 the case had gone cold.
CNN's Kevin Bohn, Kelli Arena and Mike Ahlers contributed to this report.