The Justice Department and the FBI identified Maryland scientist Bruce E. Ivins as having single-handedly carried out the attacks that killed five people and seriously sickened 17 others. The department was on the verge of seeking an indictment in 2008 when Mr. Ivins took his own life.

Doubts lingered about Mr. Ivins's guilt, in part because the FBI had had its sights on a different Maryland scientist for several years before admitting he was not the culprit. Now, a report by the National Academy of Sciences (NAS) raises new questions about whether Mr. Ivins was wrongly accused.

The lengthy report cites several instances in which the Justice Department appears to have overstated the strength of the scientific evidence against Mr. Ivins. For example, the department concluded that anthrax spores derived from the RMR-1029 vial in Mr. Ivins's lab were used in the deadly attacks. The report takes exception. "We find the scientific evidence to be consistent with their conclusions but not as definitive as stated," said Lehigh University President Alice Gast, who led the NAS committee. The report insinuates throughout that FBI failure to perform more tests or to be more precise could have erroneously eliminated other suspects or prematurely settled on Mr. Ivins as a suspect.

Yet the report itself is at times misleading. Take, for example, the FBI's assertion that Mr. Ivins deceived investigators by providing a sample purported to be from RMR-1029 but that the FBI concluded could not have come from that particular batch. "The genetic evidence that a disputed sample submitted by the suspect came from a source other than RMR-1029 was weaker" than stated by the Justice Department, the committee said. How much weaker? The NAS panel concluded that there was a 1 percent chance that the sample came from the key vial; that answer could be found only deep in the bowels of the document.

The NAS committee should not be blamed for nitpicking over the test results; that is essentially what it was tasked to do by the FBI, which commissioned its report. But the result is not satisfying - nor is it conclusive.

Congress should convene a nonpartisan commission staffed with individuals experienced in law enforcement to probe all of the evidence in the case, including that which the FBI claims shows Mr. Ivins had the opportunity and the wherewithal to carry out the 2001 attack. The inquiry should explore why and how the Justice Department eliminated other scientists who had access to RMR-1029 as suspects, and it should examine the security protocols at repositories for biological weapons. The exploration also should focus on the country's preparedness to deal with such an attack in the future.