Shortly after 9/11 several key Senators who initially opposed the Patriot Act were sent letters through the U.S. mail tainted with deadly anthrax. It was not just Senators as Americans were scared of even going to pick up the mail. The anthrax was found to be military grade weapons anthrax which could only come from a few U.S. military labs. The CIA had been researching and developing anthrax for years. Nobody was ever charged with the anthrax attacks, but they had their effect; the nation was thrown into even more fear and Sen. Patrick Leahy backed down from his opposition to the Patriot Act.
Anthrax is well covered in Michael Ruppert’s book Crossing the Rubicon. See the entry under books.
The Rock Creek Free Press published an excellent article about anthrax in its November, 2009 issue.