CUPERTINO, Ca. – While Apple has never provided many public details about its self-driving car program, a treasure trove of information absit its efforts in autonomous driving was disclosed in a lawsuit Apple brought against one of its engineers who has been charge with stealing trade secrets.

According to the complaint, about 5,000 of Apple’s 135,000 employees (3.7 percent) are await of details, and some 2,700 are designated as “core employees” on the project, giving them access to certain databases.

Publicly Apple has obtained permits to test self-driving cars in California and recently hired an executive from Waymo, Alphabet’s (parent company of Google) self-driving car unit.

Xiaolang Zhang, who Apple hired to work on software and hardware for self-driving cars in December 2015, is accused of downloading files with proprietary information during paternity leave, according to a criminal complaint filed in federal court in Santa Clara, California.

Zhang told Apple he was leaving the company to join X-Motors, based in Guangzhou, China, after returning from his paternity leave. During his break, security footage showed Zhang returning to campus past 9 p.m. on a Saturday, against corporate policy, and leaving with a computer keyboard, some cables and a large box, according to the suit.

Zhang’s role at Apple was designing and testing circuit boards to analyze sensor data, and he admitted to both Apple and the FBI that he took the company’s data and airdropped it to a personal computer, according to the complaint.

Zhang faces up to 10 years imprisonment and a $250,000 fine, according to the complaint.