Over the past week the media was gripped by the news that the FBI was about to charge Bruce Ivins, a leading anthrax expert, as the man responsible for the anthrax letter attacks in September/October 2001.

But despite the seemingly powerful narrative that Ivins committed suicide because investigators were closing in, this is still far from a shut case. The FBI needs to explain why it zeroed in on Ivins, how he could have made the anthrax mailed to lawmakers and the media, and how he (or anyone else) could have pulled off the...