"I could not erase the sense of helplessness of that man and young girl who saw their families sold right before their eyes," he recalled. "It tormented me."
An additional 350 wait in his safe houses north of the winding Tumen River, which forms the border. On one side is North Korea, a land where famine has killed an estimated 2 million people in the last decade. On the other is northeastern China, where markets groan with beef, apples, bananas, green vegetables, spices and the Korean staple, kimchi.
North Korea comes clearly into view from some vantage points on the Chinese side. Occasionally, a soldier can be seen sitting on the riverbank. Along one bend, a huge portrait of Kim Il Sung stares down from a bucolic railroad station. Bald mountains, stripped of trees for firewood, expose their bulging ribs.
The North Korean town of Namyang, seen through a pay-per-view telescope, seems eerily unpopulated; its low-slung buildings appear to be mostly empty.
Refugees say daily existence there is filled with horrors. They report that they subsisted on roots and leaves boiled into putrid soups; witnessed authorities shooting people who stole corn from the fields; saw loved ones starve to death and buried them in old rice sacks on mountain slopes packed with bodies.
In order to get out, North Koreans might use a watch, trinket or the equivalent of a few dollars to bribe the bedraggled guards sitting sentry every few hundred feet. Or they might evade the guards and then wade or swim to the sparsely guarded Chinese side. In winter, they can trot across the river's icy bends.
Once in China, poor and malnourished children have prowled the open-air market in Tumen to beg for food. Adults sought out work on farms or in factories. Some have been desperate enough to storm into diplomatic missions in a bid to gain sanctuary.
Their presence has become increasingly uncomfortable for authorities, and China has been cracking down. China considers the North Koreans economic, rather than political, refugees--people who, like millions around the world, simply seek a better life elsewhere. It has a treaty with North Korea, traditionally an ally, to return the refugees. North Korean soldiers also have crossed the porous border to round them up.
Although refugees can blend in physically because the area is heavily ethnic Korean, those who can't speak at least rudimentary Mandarin rarely venture outdoors.
The underground railroad is one of the few ways out of this predicament. Refugees know that it is largely run by Christian missionaries. Even though it is an alien concept for people brought up in an atheist society, they know that it improves their odds if they are religious -- or at least pretend to be.
They also learn that the South Korean government provides each defector a relocation bonus of about $28,000, housing, and job training -- an astounding package for people who have earned at most a few hundred dollars their entire lives.
Divorced with two children in their early 20s, Chun, 46, has an easy laugh and a quick wit that he uses to put edgy refugees at ease. He worked his way up from waiting tables to managing a hotel in Seoul, which he did for 17 years. Flush with success, he launched ventures that boomed and failed, including a golf equipment business in Tokyo and a Japanese-style restaurant in Seoul. The failed ventures saddled him with $200,000 in debt. He sold his home and furnishings and sent his children to live with friends.
For months, he subsisted on noodles and scraped together subway fare. He contemplated suicide and kept a bottle of pills handy. He gradually came to view the tough times as a sign from God that he wasn't meant to be a capitalist. He is studying now to be a Presbyterian minister.
Drawn to helping North Koreans and the idea of unifying the two Koreas, he established a mission he named Durihana, meaning "two become one." It survived on donations from about 600 subscribers. Providence seems to smile on him just when he is most desperate, Chun says. Once when he had run out of money, one of the largest churches in Seoul, Durae Presbyterian, gave him $10,000 to help the North Koreans.
Chun's mission pays for safe houses in China. For food. For train tickets to the border. And for Korean-language Bibles. He takes most of the refugees through Mongolia, but has routes through the jungles of Vietnam and on to sympathetic, non-Communist countries such as Thailand and Cambodia.
Maps of the escape routes decorate the walls of the modest apartment four flights above a restaurant that serves as both Chun's home and Durihana's offices.
Before heading to China to pick up a group of refugees, he quietly lays the groundwork with the South Korean government. The underground railroad is so sensitive that top South Korean officials say little about it on the record. It is not clear how they feel about Chun. However, Chun says five government agents regularly tail him in Seoul.