Federal prosecutors have charged a former Apple employee with stealing trade secrets related to Apple's autonomous vehicle program.

Xiaolang Zhang allegedly worked on Apple’s secretive self-driving-car project. Zhang left Apple in April saying he was going to work for a Chinese electric vehicle company called Xpeng Motors. He is accused of copying more than 40 GB of Apple intellectual property to his wife's laptop before leaving the company, according to court documents. The documents do not accuse Xpeng Motors of wrongdoing.

In a statement, Xpeng said it was "stunned and outraged" by the charges against Zhang, who had joined the company in May. Xpeng said it conducted an investigation, advised by the law firm Morrison and Foerster, and "very quickly thereafter, terminated Xiaolang's employment for cause." Apple did not respond to a request for comment.

Apple has been reported to be developing self-driving-vehicle technology for several years, though the company has been tight-lipped about its plans and ambitions. Bloomberg reported in January that the company had registered 27 self-driving test vehicles with California’s Department of Motor Vehicles. CEO Tim Cook acknowledged last year that the company was developing autonomous-car technology; that followed reports that Apple had given up on plans to build its own car.

Zhang’s arrest comes amid growing tension between the US and China, largely around the treatment of intellectual property. China requires foreign tech firms that want to do business in the country to partner with domestic companies and share or license their intellectual property with those partners. Many companies believe that Chinese companies use this process, called technology transfer, to steal their trade secrets. The Trump administration's tariffs are in part a response to this practice, but China has thus far refused to end it.

The Zhang case highlights other ways that Chinese companies could still get their hands on US companies' IP.

LEARN MORE The WIRED Guide to Self-Driving Cars

According to the court documents, Zhang was hired by Apple to work on the autonomous vehicle project in 2015. In April, Zhang took paternity leave and traveled to China. On April 30, he informed Apple that he was resigning from the company and planned to return to China to be closer to his family and work for Xpeng Motors.

During an internal investigation, Apple discovered that Zhang had downloaded "copious" pages of information, including Apple IP from company databases, in the days before his resignation and, against company policy, had taken Apple property during his paternity leave.

Zhang admitted to Apple's security staff that he had taken home a Linux server belonging to Apple and had transferred data to his wife's laptop. He said he wanted to review the data for his own education, hoping it would help him secure another job within Apple. He returned the server and brought the laptop into Apple for examination.

Zhang was arrested July 7 at Mineta San Jose International Airport. He had booked a flight to Hangzhou, China.

According to its website, Xpeng Motors was founded in 2014 and is headquartered in Guangzhou, China. It received an investment from Chinese ecommerce giant Alibaba last year, according to Tech in Asia, as well as Huawei, Xiaomi, and Foxconn, according to PanDaily. The company announced a car with "self-parking" and other autonomous car features at the Consumer Electronics Show in January.

UPDATE, July 10, 11PM: This article was updated to include a statement from Xpeng.

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