Assessing the fallout from an exposed spy operation can be difficult, but the episode was considered particularly damaging. The number of American assets lost in China, officials said, rivaled those lost in the Soviet Union and Russia during the betrayals of both Aldrich Ames and Robert Hanssen, formerly of the C.I.A. and the F.B.I., who divulged intelligence operations to Moscow for years.
The previously unreported episode shows how successful the Chinese were in disrupting American spying efforts and stealing secrets years before a well-publicized breach in 2015 gave Beijing access to thousands of government personnel records, including intelligence contractors. The C.I.A. considers spying in China one of its top priorities, but the country’s extensive security apparatus makes it exceptionally hard for Western spy services to develop sources there.
At a time when the C.I.A. is trying to figure out how some of its most sensitive documents were leaked onto the internet two months ago by WikiLeaks, and the F.B.I. investigates possible ties between President Trump’s campaign and Russia, the unsettled nature of the China investigation demonstrates the difficulty of conducting counterespionage investigations into sophisticated spy services like those in Russia and China.
The C.I.A. and the F.B.I. both declined to comment.
Details about the investigation have been tightly held. Ten current and former American officials described the investigation on the condition of anonymity because they did not want to be identified discussing the information.
The first signs of trouble emerged…