Two people have been indicted on charges related to the theft of an estimated $40 million worth of trade secrets at General Motors.

According to a federal indictment that was unsealed on Thursday, former GM engineer Shanshan Du deliberately asked for a transfer three years after she started working for the automaker in order to gain access to its hybrid technology. Du allegedly began copying documents about GM's hybrid technology in late 2003, and continued to copy documents even after receiving a severance offer from the automaker in 2005. Du's husband, Yu Qin, is also charged in the case.

The indictment noted that Qin told people in 2005 that he had a deal to provide hybrid technology to the Chinese automaker Chery Automobile. In addition, Du and Qin had created their own company, known as Millennium Technology International.

Despite the alleged theft of information related to GM's hybrid technology, there is no evidence that the Chinese benefited, said Assistant U.S. Attorney Cathleen Corken. Du and Qin have pleaded not guilty to the charges against them, which include conspiracy and fraud. They could face up to 20 years in prison if convicted.