For about two years, Xiaolang Zhang was privy to information to which many in the tech world can only dream of having access: the inner workings of Apple’s secretive autonomous car research.

During the weekend, the former Apple engineer was arrested by U.S. authorities at San Jose International Airport while preparing to board a flight to China and charged with stealing proprietary information related to Apple’s self-driving car project. At the time of his arrest, he said he was working for a Chinese start-up that is also developing autonomous vehicles, according to a criminal complaint filed in federal court in San Jose on Monday by the FBI and the U.S. attorney’s office.

Zhang, who started working at Apple in December 2015, was accused of downloading files that included engineering schematics and technical reports before leaving to work for Xiaopeng Motors, a Guangzhou-based company also known as XMotors, documents said.