One week after the attack on the World Trade Center on September 11, 2001, powdered anthrax spores were sent through the public mail system to addresses in the United States, resulting in 22 cases of anthrax with 5 deaths. This act of bioterrorism was perpetrated using letters addressed to public media headquarters, including the major television networks. The first letters were followed a few weeks later by letters sent to the offices of senators Thomas Daschle of South Dakota and Patrick Leahy of Vermont. The infections and deaths sent a wave of fear throughout the American public, and the investigation that followed has yet to lead to conclusive results about the perpetrator(s) of this act of terrorism.