The investigation of the 2001 anthrax attacks ended as far as the public knew on July 29, 2008, with the death of Bruce Ivins, a senior biodefense researcher at the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID) in Fort Detrick, Md. The cause of death was an overdose of the painkiller Tylenol. No autopsy was performed, and there was no suicide note.

Less than a week after his apparent suicide, the FBI declared Ivins to have been the sole perpetrator of the 2001 Anthrax attacks, and the person who mailed...