This century’s most notorious bioterrorism case might not be clinched as tightly as FBI investigators would have us think. There's renewed interest in the 2001 anthrax attacks that killed five people and sickened others in the wake of two reports—one by scientists and another by a collaboration of media outlets. One implication of the reports is that the true culprit in the attacks might still be free.

The reports take aim at a lengthy FBI investigation that eventually zeroed in on Bruce Ivins, a U.S. Army Medical Research Institute of Infectious Diseases microbiologist. The FBI named him the lone suspect responsible for mailing letters containing anthrax spores to U.S. senators and several media outlets. Ivins, who committed suicide in 2008, was never indicted, but the FBI maintained his guilt and closed the case last year.

That conclusion has been questioned by some in the scientific community, including a National Academy of Sciences committee and, most recently, the authors of a report posted Saturday in the Journal of Bioterrorism and Biodefense.

“Critical scientific questions, some of which have already been indicated in this paper, must be answered before the anthrax case can be laid to rest,” the authors write. “That will require scientific expertise and political neutrality, ideally with full access to all that the FBI knows.… Indeed, further scientific investigation may be the only way to bring the facts of the case to light.”

The report’s authors—anthrax expert Martin Hugh-Jones, biologist Barbara Hatch Rosenberg, and chemist Stuart Jacobsen—say their analysis casts enough doubts on the FBI case to reopen the investigation, according to the New York Times. Among those doubts is skepticism that Ivins could or would have produced anthrax spores with a “tin-silicon coating” like that found on the mailed spores.

“It indicates a very special processing, and expertise,” Hugh-Jones told the Times, adding that the process was “far more sophisticated than needed.”

Other scientists and the FBI disagree. They say the authors, who have been outspoken critics of the investigation, aren’t allowing for the fact that the tin and silicon could just as easily be contaminants from lab containers, water, or disinfectants.

“Speculation regarding certain characteristics of the spores is just that—speculation,” Justice Department Spokesman Dean Boyd told the Times. “We stand by our conclusion.”

Hugh-Jones and colleagues focused on the chemical signature of the spores, but the FBI’s scientific evidence against Ivins is mainly genetic tests linking the mailed anthrax to anthrax Ivins created in a flask labeled RMR-1029. While a genetic link isn’t in dispute, the National Academy of Sciences report states that the parentage of the spores didn’t conclusively tie Ivins to the mailings. Paul Keim, a geneticist who examined some of the anthrax samples for the FBI, ascribed the inconclusiveness of the investigation to Ivins' premature death.

“The results were consistent with RMR-1029 being the source,” he told the Los Angeles Times. If the case had gone to court, he said, “I believe that additional work would have been done to make the linkage stronger.”

Science notwithstanding, other aspects of the FBI case have come into question, thanks to an exhaustive examination by ProPublica, PBS Frontline, and McClatchy. The joint project presents evidence poking holes in several FBI opinions, including that Ivins’ work hours before the anthrax mailings was suspicious, that the pending demise of the anthrax vaccination program gave him motive, and that Ivins—who initially worked with the FBI to solve the case—mislead investigators with altered samples.

The Government Accountability Office is also reviewing the FBI case, but many of those unconvinced of Ivins’ guilt are equally unconvinced that the case will be reopened. Iowa Senator Charles Grassley, a vocal critic of the investigation, told ProPublica that even Congress was no match for the will of the FBI.

“I would question my capability of raising enough heat [to reopen the case] when you're up against the FBI,” he said. “And I've been up against the FBI.”

The matter could be farther reaching than a little bureaucratic recalcitrance. It could, as one genetics consultant on the case points out, be an instance of wishful thinking meets willing ignorance—with the end result of compromising public safety.

“For an awful lot of people, there is a desire to really want to say that yes, Ivins was the perpetrator. This case can reasonably be closed,” Claire Fraser-Liggett is quoted as saying in the collaborative piece. “But I think part of what's driving that is the fact that, if he wasn't the perpetrator, then it means that person is still out there.”