Zachary T. Fardon, the former top federal prosecutor in Chicago, is returning to the international firm King & Spalding to launch and lead a new office in the city.Fardon will serve as the managing partner and head of litigation of the new office, which is expected to open in a permanent location in the West Loop in September.Fardon became the U.S. attorney for the Northern District of Illinois in 2013 and resigned in March along with 45 other U.S. attorneys who were asked to do so by the Trump administration.After …