Ivins, 62, took a fatal dose of acetaminophen last month as prosecutors prepared to indict him for murder.
Top FBI officials and a handful of prominent scientists who aided the investigation presented more - but not all - of the scientific case against Ivins in a two-hour-and-fifteen-minute news conference to try to quell suspicions of outside scientists, some of whom were friends of the suspect.
At times the officials and scientists contradicted themselves, even down to the number of flasks containing the anthrax Ivins had. They eventually agreed it was one one-liter triangular flask capped with cheesecloth that linked Ivins to the attacks.
"There were a lot of lessons learned," FBI Assistant Director Vahid Majidi said. "Were we perfect? Absolutely not. We've had missteps, and those are the lessons learned. ... It was over the last few years that we were able to incorporate all of the lessons learned that we have throughout this investigation."
The complete genome mapping of the unique killer strain - the cornerstone of the forensic case - won't be public for months, maybe more than a year, because it will be published in peer-reviewed scientific journals that take time. The outsiders who had questions about the government's case wanted to see the complete genomic map sooner.
"There are still many nagging questions about this," said Dr. Michael Stebbins, who directs the Federation of American Scientists' biosecurity project and wasn't at the Monday's briefing. "Unfortunately a lot of them are not going to be able to be answered in the immediate future."
Majidi understands that: "I don't think, No. 1, we're ever going to put the suspicions to bed. There's always going to be a spore on the grassy knoll."
FBI officials spent much of their time going into more detail about the specific four mutations in the strain of anthrax that led back to Ivins' Army lab at Fort Detrick, Md. They weren't easy to find, rare like red or green M&Ms in a flask mostly full of blue candies, Majidi said.
FBI officials and scientists had to come up with a technique for looking at the DNA of anthrax to whittle down the list of labs and suspects who could have produced it, creating a new field of forensic microbiology. That scientific technique to connect a lab with a unique strain wasn't available until after the FBI had destroyed its first sample from Ivins.
In February 2002, the FBI sent subpoenas around the world to labs handling the Ames strain of anthrax, which was the strain that killed five people in 2001. They got 1,070 samples and destroyed only one: the first one from Ivins. It was destroyed because Ivins didn't use the proper test tube and growth medium so it may have not been useful as evidence in court, officials said.
Ivins was one of the first to respond to FBI subpoenas, but his sample was deemed useless and he was asked to submit another. He gave investigators a second sample of anthrax from his lab in April 2002 to comply with standards in a subpoena issued in the case. But that sample contained a different strain than what he submitted two months earlier in what prosecutors call an attempt to deceive or confuse investigators.
When Ivins sent his initial sample to the FBI, a duplicate went to the lab of Dr. Paul Keim, a geneticist at Northern Arizona University in Flagstaff, Ariz.
Keim still had his RMR-1029 sample in 2006 when the FBI realized it could match Ivins to two batches of anthrax-laced letters that were mailed in the weeks after the Sept. 11, 2001, terror attacks.
Stebbins said the fact that Keim kept his sample was key in building the case, something Keim played down after the news conference.
FBI officials and scientists also played down any significance of the element silicon in the killer anthrax strain, saying it seemed more of a natural occurrence than deliberate weaponizing as once theorized early in the investigation.
One of the targets of the letters was former Senate Democratic leader Tom Daschle, who on Monday called the evidence against Ivins convincing - even if he is not completely sure the investigation focused on the right person.
In an interview, Daschle praised the investigation and said his two-hour FBI briefing last week was "complete and persuasive." Still, he said, there are some open questions. He said the evidence should be scientifically reviewed.
Daschle said the most compelling evidence to him is the odd, extended hours that the Army scientist kept shortly after the Sept. 11 attacks.
"He had no real explanation for the significant increase," Daschle said. "His only response was that he wanted to hang out there, which was not a very compelling reason."
Daschle and fellow Democratic Sen. Patrick Leahy of Vermont both received anthrax-laced letters in their Senate offices. Both senators have received recent briefings from FBI Director Robert Mueller on the evidence against Ivins.