The case was unprecedented: On Oct. 10, Belgium extradited a Chinese intelligence officer to the United States after an Ohio court had indicted the operative on charges of "economic espionage involving theft of trade secrets from leading U.S. aviation companies." Belgian authorities arrested Xu Yanjun, a deputy division director of the Sixth Bureau of China's State Security Ministry in Jiangsu, on April 1 in Brussels based on an arrest warrant issued in connection with a U.S. criminal complaint. Once Belgian authorities extradited Xu to the United States on Oct. 10, American authorities unsealed the indictment and the initial criminal complaint....