Editor's note: In the wake of the 9/11 attacks, the United States faced a second wave of terrorism: anthrax-tainted letters. The investigation lasted seven years, and meandered along a path that included phony leads, blind alleys, and scientific hurdles. Could it happen again? Watch "CNN Presents: Death by Mail" on Sunday, Oct. 2 at 8p/11p ET.
(CNN) -- Nancy Haigwood's career as a scientific researcher in Seattle was on the rise in 2001, when her memory of a sorority-obsessed university classmate helped lead federal investigators to the man they say was responsible for the anthrax attacks in the months following 9/11. But for the first four and a half years, her tip was low priority.
Ten years ago, anthrax-laced letters began showing up at the U.S. Capitol and news agencies in Florida and New York. The anthrax attacks in the fall of 2001 killed five people and sickened 17 others.
In the beginning, the anthrax letters seemed like the work of Islamist extremists. They were postmarked within weeks of the September 11 attacks, and the letters sent to then-Senate Majority Leader Tom Daschle and Sen. Patrick Leahy declared "Death to America. Death to Israel."
But based on a recurring mixture of Arabic and English expressions in the letters ("Allah is Great") and the high quality of the anthrax spores that spilled out of the envelopes, the FBI announced in November 2001 that it was looking for a rogue insider.
The suspect was not an al Qaeda jihadist, the FBI believed, but more likely someone from within the biotech industry.
The FBI e-mailed members of the American Society for Microbiology in January 2002 asking for help. The feds suspected the anthrax mailer could be a researcher or technician with legitimate access to deadly germs and a high degree of technical knowledge.
"It is very likely that one or more of you know this individual," the FBI's e-mail said.
Out of 43,000 e-mails, only one person responded: Nancy Haigwood.
"It was as though something clicked," she said in a recent interview from her lab in Portland, Oregon where she directs one of eight National Primate Research Centers. "I just thought I might actually know the person."
The Kappa connection
Haigwood had met Bruce Ivins in the mid-1970s during graduate school at the University of North Carolina at Chapel Hill. She recalled his incessant questions about her sorority, Kappa Kappa Gamma.
Having joined the sorority as an undergraduate, Haigwood stayed involved as the adult adviser at the UNC chapter. Ivins, she says, always asked her for information about Kappa Kappa Gamma.
"Every time I talked to him, nearly, he would mention it," says Haigwood. "And finally I said, 'You know, Bruce, that's enough!'"
Ivins' obsession with Haigwood and her sorority continued years after they graduated from UNC. Ivins had started his job at the U.S. Army Medical Research Institute for Infectious Diseases -- USAMRIID -- at Fort Detrick, Maryland, in 1980. Haigwood, too, was living and working in suburban Washington.
One day in 1982, she came home to find her sidewalk, fence and car spray-painted with red graffiti: "K K Γ" -- the Greek letters of her sorority.
"Because of the Kappa connection, I immediately thought of Bruce Ivins," Haigwood said.
Five months later, the Frederick News-Post published a letter to the editor under Haigwood's name. The author, purporting to be "a member of Kappa Kappa Gamma," defended fraternity and sorority hazing by as a way to "strengthen the mettle of pledges" and "build loyalty ... in the all-important weeding-out process."
Nothing could have been further from Haigwood's true beliefs, she says.
After calling the newspaper to disavow the letter, Haigwood called Ivins to confront him. "I said, 'This can only be you and you have to stop'" Haigwood says. "He said he didn't do it. But, of course, then, I knew he was lying."
Ivins investigates the crime
In 2001, as the anthrax letters terrorized the country, Ivins still worked at Fort Detrick's bio-weapons defense institute, USAMRIID, as a civilian microbiologist and one of the agency's top anthrax experts.
The institute houses the Pentagon's main laboratories for developing vaccines to protect against biological weapons.
Former colleague Gerry Andrews described Ivins as an "outgoing, friendly guy" with a "wry sense of humor."
Ivins was "quirky, socially awkward," according to Lt. Col. Jeffrey Adamovicz, a retired Fort Detrick microbiologist.
But none of his colleagues seemed to know that Ivins had a secret, double life plagued by mental health problems so severe that psychiatrists would later describe him as "a predator."
When the anthrax letters first started showing up, federal agents turned to Fort Detrick researchers for help with their investigation.
But realizing that the scientists with the expertise to solve the crime also had the expertise to commit it, investigators administered polygraph exams to some of the USAMRIID staff.
Ivins seemed to pass, although experts would later question those results.
He was soon hard at work analyzing the deadly powdered anthrax spores.
On November 14, 2001, Ivins e-mailed photos of himself to Nancy Haigwood, as well as former colleagues and family members, that showed him working with what he called "the now infamous" strain of anthrax used in the attacks.
The e-mail was striking, says Haigwood, because "we publish our work. We talk about it at conferences. [But] we don't e-mail photos with anthrax."
To Haigwood, it seemed that Ivins "wanted his former colleagues and friends to know that he was doing important work.
"To me, he was projecting, 'Look at me, I'm working with anthrax, in case you forgot,'" she said.
One picture stood out: a photo of Ivins without gloves supposedly handling a sample of anthrax. Haigwood interpreted this lack of the most rudimentary protection as a bragging message from Ivins, "a sign [that] 'I'm immune.'"
"It was more an 'Oh, no!' than an 'Aha!' moment," she says.
That's what triggered her call to the FBI in February 2002.
"We didn't know [then] how it related to the crime," says Thomas Dellafera, the U.S. Postal Inspection Service team leader on the anthrax investigation. "So, at that time, it sort of was tabled, if you will."
He says her information "was put in ... the Bruce Ivins file" and she was asked to stay in touch with Ivins and keep everyone posted.
Meanwhile, federal investigators began focusing on former USAMRIID researcher Steven Hatfill.
The wrong man
At the time of the anthrax attacks, Steven Hatfill worked at SAIC, a government contractor. Before the attacks, he had proposed a study on the risk of anthrax being sent through the mail, which included PowerPoint presentations about a "single letter" being sent to "government agencies" and "news agencies."
"That was very interesting to us," said Dellafera of the U.S. Postal Inspection Service. "That is what happened. Almost prescient, right?"
Hatfill said the material was for his consulting work training first responders, doctors and Army medics in how to handle biological threats.
But, according to the government, eight people flagged Hatfill to investigators as a possible suspect. Federal agents searched his apartment in June 2002, and two months later, then-U.S. Attorney General John Ashcroft labeled him a "person of interest."
"I am not the anthrax killer," Hatfill declared in a statement to the news media. "I have never, ever worked with anthrax in my life."
But, adding to the suspicion, Hatfill had a series of prescriptions for Cipro, the antibiotic of choice for treating anthrax. The government would eventually acknowledge that Hatfill used the Cipro to treat a recurrent sinus infection.
In 2003, Hatfill sued the government for leaking information about him to the news media, alleged violations of the Privacy Act. Five years later, the government settled the case by paying Hatfill $5.8 million. As for the criminal investigation, the government would later acknowledge that Hatfill was innocent.
FBI closes case, but questions still linger
After a lull in the case, investigators in 2006 turned their attention to Bruce Ivins.
"Those years, he was not an apparent suspect, not a serious suspect," Nancy Haigwood said, referring to the more than four years after she first alerted the FBI about Ivins. "And then the vise started to squeeze."
Federal agents had documented a pattern of Ivins' after-hours work in his lab, alone, shortly before the anthrax letters were mailed. Scientists hired by the FBI had matched four genetic mutations in the attack anthrax to the same mutations in a flask of anthrax in Ivins' lab, labeled RMR-1029. And investigators noted Ivins' own words, referring in his e-mails to his deep psychological problems -- "being eaten alive inside" by what he called "paranoid, delusional thoughts."
More than six years into the anthrax investigation, according to investigators, Ivins would admit to authorities that he had written the letter to the Frederick News-Post under Nancy Haigwood's name. He also admitted to vandalizing her home in 1982 and breaking into two Kappa Kappa Gamma houses to steal material on the sorority's secret codes and rituals.
Ivins told investigators, "It's more than an interest in KKG; it's an obsession," according to Edward Montooth, the then-FBI Inspector in charge.
Federal agents say Ivins traced his twisted relationship with Kappa Kappa Gamma back to his college days at the University of Cincinnati. By his own account, Ivins was turned down for a date by a fellow undergraduate, a member of the sorority, and his resentment festered for 40 years.
Investigators were beginning to make a connection between his sorority obsession and the anthrax letters.
Ivins denied having anything to do with the anthrax letters. And investigators had no direct evidence linking Ivins to the crime: no DNA on the letters, no fingerprints, no eyewitness.
"How [the anthrax] was made, how it was prepared, where it was done, over what period of time -- there's a total void of evidence," Ivins' attorney, Paul Kemp, said in a recent CNN interview.
Many of his former colleagues say Ivins could not have made that much dried anthrax at the Fort Detrick facility without being detected.
But by July 2008, federal prosecutors believed they had enough circumstantial evidence to indict Ivins for use of a weapon of mass destruction -- a potential death-penalty crime.
They theorized that his motive was to boost interest and funding for a new anthrax vaccine he had helped to invent, which he apparently feared had become a low priority.
Before Ivins could be charged, he took an overdose of an over-the-counter painkiller. He was pronounced dead on July 29, 2008.
In 2010, federal authorities formally closed their investigation, summarizing that "Ivins alone mailed the anthrax letters."
Prosecutors were convinced they had solved a crucial aspect of the mystery: why the anthrax letters were mailed from Princeton, New Jersey. The nondescript but heavily contaminated drop box was on Nassau Street -- across from Princeton University.
It had taken several years from the time Nancy Haigwood first contacted the FBI about Bruce Ivins for investigators to make what they believe to be the critical connection:
The mailbox on Nassau Street was just a few doors from a building that leased office space to a sorority: Kappa Kappa Gamma.