In the fall of 2001 envelopes carrying deadly anthrax were delivered to U.S. Senate offices, network news divisions and a tabloid newspaper. Now, new questions are being raised about the most expensive and complex investigation ever undertaken by the FBI. FRONTLINE, in a co-production with ProPublica and McClatchy Newspapers, takes a hard look at the FBI's investigation of the country's most notorious act of bioterrorism.
—Anonymous