“In spy-speak it is known as a ‘walk-in’—an unsolicited approach to a diplomatic mission by a foreigner claiming to have sensitive information. And when an agitated former police chief, Wang Lijun, entered a U.S. consulate in early February with an eye-popping tale about the death of a British citizen, the stakes could hardly have been higher.”
Source: As Scandal Shook China, Quiet Spy Game Unraveled – WSJ.com