He is sometimes known under his pseudonym Nam Hong-chul, which he used to maintain his anonymity while in northeast China working to help fellow defectors reach South Korea.
[2] While in China, he worked at odd jobs in construction and manual labour; eventually, he grew weary of living in fear of arrest and deportation to North Korea by Chinese police, and gave up his son to the custody of a family of ethnic Koreans with Chinese citizenship, hoping to give him a better life.
With the assistance of defector aid organisation Durihana, he was able to locate his son, and make arrangements for people smugglers to bring him out of China to Mongolia and from there to Korea.
Yoo's grief led him to convert to Christianity, and also to pledge to help smuggle fellow defectors out of China.
[2] In October 2007, he was arrested in a Chinese police operation aimed at dismantling the escape network, and threatened with repatriation to North Korea, despite his South Korean citizenship.