(NBC NEWS) — A former CIA officer who was charged Tuesday with unlawful possession of secrets is suspected of a much worse crime: betraying U.S. informants in China, sources familiar with the case told NBC News.

The former officer, Jerry Chun Shing Lee, 53, was arrested Monday after flying into New York on a Cathay Pacific flight from his home in Hong King, federal authorities announced.

Lee, who is a naturalized U.S. citizen, was charged with a single count of unlawfully possessing national defense information, based on a 2012 search that found him to be in possession of two notebooks containing the true names of CIA assets and covert facilities, which are some of the agency’s most closely guarded secrets.

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