The recent arrests came right after the FBI had defeated a Chinese attempt to illegally obtain carbon fiber for their new fighter jets. The item in question is M60JB carbon fiber, which sells for $2,000 a kilogram (nearly twice what silver goes for these days) and is an essential component of China's stealth fighters (the J-20 and J-31) which are still in development. Obviously China has already obtained some of this carbon fiber but in this case was negotiating to obtain two tons of the stuff.
A Chinese citizen, Ming Suan Zhang, was charged with trying to illegally export the fiber and could get up to 20 years in prison, unless he makes a deal with the U.S. government to provide more information on Chinese smuggling operations. China has been illegally obtaining materials and devices for decades. While Internet based espionage makes it easier to steal documents, there is often a need for more tangible items, like two tons of carbon fiber.