Laramie, Wyo.

ON Wednesday, the United States Justice Department revealed its evidence that Dr. Bruce E. Ivins, on his own, committed the worst act of bioterrorism in the country’s history. This 18-year veteran scientist of the United States Army Medical Research Institute of Infectious Diseases at Fort Detrick in Frederick, Md., is accused of killing five people and sickening 17 others in the fall of 2001. Dr. Ivins died on July 29 of an apparent suicide without a chance to give his side of the story.

After reading the affidavits and listening to the Justice Department briefing, I was both disheartened and perplexed by the lack of physical evidence supporting a conviction.

Dr. Ivins was a friend and colleague of mine for nearly 16 years. We worked together at Fort Detrick. He was a senior scientist, and I was, first, a bench scientist and, from 1999 to 2003, the chief of the bacteriology division.

The Justice Department has presented different types of evidence to support its argument that Dr. Ivins was the person who mailed anthrax to Tom Brokaw, Tom Daschle and others in September and October of 2001. Much of this evidence is outside the realm of science: Dr. Ivins’s alleged fixation with a sorority; strange comments in excerpts from his e-mail messages; a connection to a Greendale school that might or might not explain the fictitious return address on anthrax mailings. I will not address these points beyond noting that they are highly circumstantial.