Earlier this year, one of the most prominent North Korean defectors, Yoo Woo Sung, walked out of his apartment building in Seoul and found four South Korean government vehicles waiting for him.
Authorities hauled Yoo away and arrested him on charges of espionage. They had learned of his alleged crime, court documents show, thanks to testimony from his sister, who said Yoo had been sent on a mission by North Korea's secret police to infiltrate the defector community and pass back information about the people he met.
Yoo, 32, is being held at a detention center on the outskirts of the South Korean capital, his case a reminder of how this peninsula's messy and sometimes covert conflict has left the South on edge, with people here unsure whom they can trust.