WASHINGTON (CNN) -- Cookies mailed to the U.S. Supreme Court last year contained enough rat poison to kill all nine justices, retired member Sandra Day O'Connor said at a conference last week. Barbara Joan March, a 60-year-old Connecticut woman, was sentenced last month to 15 years in prison. She sent 14 threatening letters in April 2005 -- each with a baked good or piece of candy laced with rat poison -- to a variety of federal officials: the nine Supreme Court justices; FBI Director Robert Mueller; his deputy; the chief of naval operations; the Air Force chief of staff and...