(CNN) A former CIA case officer was sentenced to 19 years in prison this week for conspiring to provide sensitive US information to the Chinese government.

Jerry Chun Shing Lee, 55, worked for the agency for 13 years in several locations, and had intimate knowledge of its classified information and names of covert CIA officers in China.

In May, he pleaded guilty to conspiring to commit espionage on behalf of the Chinese government. At the time, his defense team said he was not a Chinese spy.

But court documents detailed how he communicated with two Chinese intelligence officers who'd send him envelopes with requests for secret information in exchange for cash. The Chinese intelligence officers asked him for 21 different pieces of information, mostly about CIA matters, court records show.

A thumb drive with secret information

In May 2010, in response to requests by the Chinese intelligence officers, Lee created a document that provided locations in which the CIA would assign officers and a sensitive operation that the CIA would assign officers with certain experience, according to court records.

After Lee created this document, he transferred it from his laptop to a thumb drive. The document included US national defense information that was classified as secret.

FBI agents who searched his Hawaii hotel room in 2012 found the thumb drive with the document. Lee told federal investigators he never delivered the thumb drive to the Chinese.

"The search also revealed that Lee possessed a day planner and an address book that contained handwritten notes made by Lee that mostly related to his work as a CIA case officer prior to 2004. These notes included, among other things, intelligence provided by CIA assets, true names of assets, operational meeting locations and phone numbers, and information about covert facilities," the Justice Department said in a statement.

A cash offer and a promise

Lee left the CIA in 2007 and moved to Hong Kong. That's where the two Chinese intelligence officers approached him three years later and offered to pay him for national defense information he'd acquired as a CIA case officer. They offered him $100,000 cash and a promise to take care of him "for life" in exchange for his cooperation, court records show.

Almost immediately after, he started receiving requests for information from the Chinese intelligence officers. Most of the requests asked for sensitive CIA information, including national defense information, court records show.

Between May 2010 and December 2013, he deposited hundreds of thousands of dollars into his bank account, according to records.

"Americans entrusted with our government's most closely held secrets have a tremendous responsibility to safeguard that information," said G. Zachary Terwilliger, US attorney for the Eastern District of Virginia.

"Instead of embracing that responsibility and honoring his commitment to not disclose national defense information, Lee sold out his country, conspired to become a spy for a foreign government and then repeatedly lied to investigators about his conduct."