(CNN) A Virginia jury Friday found former CIA case officer Kevin Mallory guilty of transmitting secret and top secret documents to Chinese spies, according to a spokesman for the US attorney in the Eastern District of Virginia.

Mallory was also convicted of lying to investigators. He faces up to life in prison.

John Demers, the assistant attorney general for national security, reacted to the verdict by saying, "it is a sad day when an American citizen is convicted of spying on behalf of a foreign power."

He added, "this act of espionage was no isolated incident. The People's Republic of China has made a sophisticated and concerted effort to steal our nation's secrets."

Mallory, a 61-year-old Virginia man, was arrested last year and charged with delivering defense information to aid a foreign government and making false statements. He entered a plea of not guilty.

During the trial that began at the end of May, a jury heard prosecutors and Mallory's defense attorneys offer up divergent explanations for a fact that Mallory admitted to: sending four pages of documents to Chinese men and receiving from them thousands of dollars that he did not properly declare on customs intake paperwork.

Prosecutors alleged that Mallory betrayed the US by selling classified information to the Chinese, while Mallory's lawyers said that he had "fallen on hard times," but remained a "loyal and patriotic American who has served his country with distinction throughout his life."

The defendant's attorneys said that he became suspicious that he was dealing with intelligence operatives and "tried to string the Chinese agents along" and warn the CIA.

Mallory is slated to face sentencing in September.