Since being arrested and charged with espionage last January, Yoo Woo-seong has figured as the main character in what is arguably South Korea's biggest spy-case in recent years.

Yoo, originally from North Korea, is accused by the South's National Intelligence Service (NIS) of having systematically handed personal information about more than 200 defectors living in the South to North Korean authorities – coveted information for a regime known for punishing the families of escapees.