Illustration: Goñi Montes

Finally, the investigation was over. The riddle solved. On August 18, 2008—after almost seven years, nearly 10,000 interviews, and millions of dollars spent developing a whole new form of microbial forensics—some of the FBI’s top brass filed into a dimly lit, flag-lined room in the bureau’s Washington, DC, headquarters. They were there to lay out the evidence proving who was responsible for the anthrax attacks that had terrified the nation in the fall of 2001.

It had been the most expensive, and arguably the toughest, case in FBI history, the assembled reporters were told. But the facts showed that Army biodefense researcher Bruce Ivins was the person responsible for killing five people and sickening 17 others in those frightening weeks after 9/11. It was Ivins, they were now certain, who had mailed the anthrax-filled letters that exposed as many as 30,000 people to the lethal spores.

The FBI unraveled the mystery, officials said, thanks in part to the microbiologists seated at a U-shaped table in the front of the room. Among them was Paul Keim, who first identified the anthrax strain used in the attacks, and genetic specialist Claire Fraser-Liggett, who led the team that sequenced the DNA of the anthrax in the letters, tracing the spores back to their genetic match: a flask of superconcentrated, ultrapure anthrax held by Ivins. Several of the researchers at the table had previously counted Ivins as a peer and even a friend. Now they were helping brand him a monster.

Between the officials and the scientists, it was a convincing display. It had to be. Ivins had killed himself three weeks earlier. There would be no arrest, no trial, no sentencing. Absent a courtroom and a verdict to provide a sense of finality or some measure of catharsis, all the FBI could do was present its findings and declare the case closed.

No one involved that day expressed any doubt about Ivins’ guilt. But things are not always as clear-cut as they may seem in an FBI presentation. Two years later, sitting in her office overlooking West Baltimore, Fraser-Liggett concedes she has reservations. “There are still some holes,” she says, staring out her window in discomfort. Nearly 2,000 miles away in Flagstaff, Arizona, Keim has his own concerns. “I don’t know if Ivins sent the letters,” he says with a hint of both irritation and sadness. Even agent Edward Montooth, who ran the FBI’s hunt for the anthrax killer, says that—while he’s still convinced Ivins was the mailer—he’s unsure of many things, from Ivins’ motivation to when he brewed up the lethal spores. “We still have a difficult time nailing down the time frame,” he says. “We don’t know when he made or dried the spores.” In other words, it’s been 10 years since the deadliest biological terror attack in US history launched a manhunt that ruined one scientist’s reputation and saw a second driven to suicide, yet nagging problems remain. Problems that add up to an unsettling reality: Despite the FBI’s assurances, it’s not at all certain that the government could have ever convicted Ivins of a crime.

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