The complaint said that the former employee, Xiaolang Zhang, disclosed intentions to work for a Chinese self-driving car startup and booked a last-minute flight to China after downloading the plan for a circuit board for the self-driving car. Authorities arrested Zhang on July 7 at the San Jose airport after he passed through a security checkpoint.

"Apple takes confidentiality and the protection of our intellectual property very seriously," Apple said in a statement. "We’re working with authorities on this matter and will do everything possible to make sure this individual and any other individuals involved are held accountable for their actions."

Tamara Crepet, a lawyer provisionally appointed to represent Zhang, did not immediately respond to a request for comment.

The criminal complaint says Zhang was hired to develop software and hardware for Apple's autonomous vehicle project, where he designed and tested circuit boards to analyze sensor data.

In April, Zhang took paternity leave following the birth of a child and traveled with his family to China, according to the complaint filed in the U.S. District Court for the Northern District of California.

When Zhang returned near the end of April he told his supervisor he planned to resign, move back to China and work for Xiaopeng Motors, an intelligent electric vehicle company headquartered there with offices in Silicon Valley, the complaint says.

Zhang's supervisor called in Apple security officials, who discovered that Zhang had run extensive searches of secret databases and had come on to Apple's campus on April 28, when he was supposed to be on paternity leave, the complaint alleges.

While on campus, the complaint alleges, Zhang took circuit boards and a computer server from a self-driving car hardware lab, and his Apple co-workers showed him a "proprietary chip."

The complaint did not state whether the chip was intended for self-driving cars. About 5,000 of Apple's 135,000 employees were allowed access to information about its self-driving car project, but only 2,700 of them had access to the secret databases that Zhang had access to, according to the complaint.

Zhang told Apple officials he had taken the hardware from the lab because he wanted to transfer to a new position within Apple and thought it would be useful to him, the complaint states.

Zhang also allegedly downloaded data to a personally owned computer, including a 25-page secret blueprint for circuit board for a self-driving car, which investigators described as "the single file" that "serves as the basis for the instant criminal charge."

Agents for the Federal Bureau of Investigation questioned Zhang and served a search warrant at his house on June 27, according to the complaints. Agents learned he had purchase a "last-minute, round trip airline ticket with no co-travelers" destined for China on July 7 and arrested Zhang at the airport, according to the complaint.