Xiaolang Zhang was arrested at the San Jose International Airport on 7 July as he was about to board a plane bound for Hangzhou.
Zhang had worked at Apple from December 2015 on a project to develop software and hardware for use in autonomous vehicles, according to the chargesheet filed by the FBI and uploaded by the site MacRumors.
He took paternity leave in April this year and visited China. On his return, he told Apple that he wished to resign as he wanted to be closer to his mother who he claimed was ill.
He also told his supervisor that he would be working for a company known as XMotors, a Chinese start-up that deals in electric vehicles and autonomous vehicle technology.
It was found that he had been accessing sections of the network reserved for those with security clearances, and downloading numerous files containing confidential information.
Zhang was also found to have been on the Apple premises at 9.14pm on 28 April, at a time when he was still on leave.
During another meeting in May, he admitted to copying material from the company's network to his wife's computer. A search of this computer revealed about 40GB of data that had been copied.
Zhang was sacked on 5 May and was said to be working for XMotors at their California office in Mountain View. He informed Apple that he would be soon relocating to Guangzhou.
Anaylsis of the files found on his wife's computer found one PDF which had electrical schematics for a circuit board that is part of Apple's proprietary technology for its self-driving car project.
The FBI based its criminal charge on this single file. The computer is in the possession of the agency after having being seized from Apple after a warrant was issued for the machine.