In a case of international industrial espionage, a former GM engineer and her husband attempted to steal trade secrets about hybrid technology and sell $40 million worth of information to a Chinese automaker.

The married couple, Shanshan Du and Yu Qin, both U.S. citizens from Troy, Mich., was indicted in federal court on July 22 on conspiracy, fraud and unauthorized possession of trade secrets. They face up to 20 years of prison, along with a series of heavy fines if convicted.

According to several reports, the couple had been under investigation since 2006. Du, who began work at GM in 2000, requested a transfer three years later to get greater access to hybrid technology. GM offered Du a buyout in 2005.

Before accepting it, she began systematically copying thousands of pages of GM documents to an external computer hard drive belonging to Millennium Technology, according to prosecutors. Qin then proposed selling that hybrid technology to Chery Automobile, a Chinese automaker.

According to Assistant U.S. Attorney Cathleen Corken, GM learned about the alleged theft late in 2005 and called the FBI.

“Theft of trade secrets is a threat to national security,” said Andrew Arena, head of the FBI in Detroit, in a statement. The FBI says the technology never reached Chinese hands.

Du and Qin have entered not-guilty pleas and were released on $10,000 bonds.