The building lost several major tenants in the early 2000s due in part to perceived terrorism risk following the September 11 attacks . In June 2006 , seven men were arrested by the FBI and charged with plotting to destroy the tower . Deputy FBI Director John Pistole described their plot as " more aspirational than operational " . The case went to court in October 2007 ; after three trials , five of the suspects were convicted and two acquitted . The alleged leader of the group , Narseal Batiste , was sentenced to 13 ½ years in prison . Meanwhile the building 's largest tenant at this time , Ernst & Young , moved to North Wacker Drive in early 2009
September 11 attacks
September 11 attacks
Willis Tower