Sweden\'s top prosecutor revealed Tuesday that his office opened a preliminary investigation of two Americans suspected of spying in 2009. Tomas Lindstrand said the men, believed to be working for the U.S. Central Intelligence Agency, were discovered conducting illegal undercover terror investigations, the Swedish news agency TT reported. The Swedish intelligence service Sapo reported the two were tracking people under investigation by Sapo for suspected terror links. Lindstrand said the investigation of the Americans was dropped when they left the country after their spying was reported by a Swedish newspaper. He said the CIA had diplomatic immunity which means its employees can be investigated but not charged.  Swedish Foreign Minister Carl Bildt said the suspected U.S. spies were not formally kicked out of Sweden.