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 attacks, acting alone.

I believe this is another mistake in the investigation.

Let's start with the anthrax in the letters to Sens. Tom Daschle and Patrick Leahy. The spores could not have been produced at the U.S. Army Medical Research Institute of Infectious Diseases, where Ivins worked, without many other people being aware of it. Furthermore, the equipment to make such a product does not exist at the institute.

Information released by the FBI over the past seven years indicates a product of exceptional quality. The product contained essentially pure spores. The particle size was 1.5 to 3 microns in diameter. There are several methods used to produce anthrax that small. But most of them require milling the spores to a size small enough that it can be inhaled into the lower reaches of the lungs. In this case, however, the anthrax spores were not milled.