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 Bruce 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.