In September 2001, just a week after the 9/11 attacks, another wave a fear began to grip the nation. It wasn't from a hijacked plane or a bomb, but from letters sent in the mail, and the white powder inside. The five envelopes were filled with a powder laced by the anthrax bacteria killed five people and sickened 17 others. It was the most notorious act of bioterrorism the country had ever seen. In 2008, Dr. Bruce Ivins, the key suspect of the nine year federal investigation committed suicide under the pressure of the intense scrutiny. After his death, investigators explained their belief that Dr. Ivins acted alone in distributing the deadly virus.

Dr. Claire Fraser-Ligget, director of the Institute for Genome Sciences at the University of Maryland, whose lab did work for the FBI in this investigation, and Michael Kirk, producer of the new PBS Frontline documentary "The Anthrax Files," re-examine this closed case to see whether FBI indicted the right suspect.