Kim Seung-chul was a 31-year-old North Korean laborer, working as a logger in Siberia.

As a graduate of the Hamhung University of Hydraulic Engineering, he was overqualified, but he took the rare opportunity to leave the country as North Korea's collapsing economy made life increasingly difficult.

He worked 13-hour days, seven days a week. For a month of work he received about $20. That was what remained after the North Korean government took its cut.

After nearly two years, he had had enough. On a cold Saturday in January 1993, he walked out of his dormitory and spent the next year hiding in Russia, Uzbekistan and Kazakhstan. In spring 1994, tired of running, Kim went to the South Korean Embassy in Kazakhstan.

Today, in Seoul, Kim runs North Korea Reform Radio, which he founded in 2007. It broadcasts programming into North Korea aimed at influencing higher-level officials to turn against the regime of Kim Jong Un.

Kim Seung-chul also receives footage, audio and documents regarding North Koreans laboring abroad, as he once did, from contacts inside the foreign work sites. He has traveled to some of them in an effort to document the workers' living conditions.

These laborers are among the few North Koreans ever allowed to leave the country. Their role is to build up the coffers of Kim Jong Un's regime. Analysts say the government takes in anywhere from $200 million to $2 billion a year.

"These are North Koreans of good 'songbun,' North Korea's ­loyalty-based system of social classification. These are people who come from a family background that's seen as safe," said Greg Scarlatoiu, executive director of the Committee for Human Rights in North Korea.

"These are married men with at least one child, even better, two children. Of course the families are kept at home as hostages, as insurance to make sure that these workers do not defect," he said.

With at least 60,000 North Korean workers in 20 countries, according to Scarlatoiu, Kim Seung-chul has his work cut out for him.

Kim shared some of the items he has gathered with The Washington Post, including undercover footage and a ledger book from a work site in Russia, and footage taken by Kim of a conversation with two laborers in Mongolia.

The footage and documents provide a rare glimpse inside North Korea's global moneymaking scheme, which has helped Kim Jong Un's regime defy international sanctions and advance the country's nuclear weapons and ballistic missile programs.

The ledger book from Russia, which along with the footage is from 2015, shows how the on-site managers collected the regime's cut from the workers' salaries.

Page after page, written in scrawled Korean, lists monetary targets and the names of workers who have fallen behind.

One page seems to offer instruction on keeping order. "Controlling the workers is possible only by fines not by monitoring. Workers pay attention only when you talk about their money in the pocket," it reads. "It might have been possible to just kill time and get paid in other work but it's different here. This company is where people have to make money and submit their targets. Wake up."

Although North Korea has been hit with round after round of international sanctions, the overseas worker program had been left out until August and September when the U.N. Security Council directly targeted the program.

In response to the sanctions, countries including Kuwait and Qatar have expelled North Korean workers or announced an end to new work visas. Poland ended visas last year.

But with at least 50,000 workers in Russia and China combined, any real hit to the scheme will be decided by how these two permanent members of the Security Council implement the sanctions.

In the past, China granted "livelihood exemptions" allowing some trade to continue in an attempt to ease the burden of sanctions on ordinary North Koreans.

But Beijing is starting to lose patience, increasing economic pressure as North Korea's ballistic missile and nuclear tests threaten to upend regional stability.

Russia, though, seems to be picking up the slack. About 29,000 North Korean laborers work there in construction and logging.

North Koreans were documented working on a stadium in St. Petersburg for the 2018 World Cup, Human Rights Watch said.

Both Russia and China pushed back against a strict draft resolution put forth at the United Nations by the United States that would have banned the laborer program altogether.

The language that was agreed upon allows North Korean workers to stay in a country for the remainder of their contracts.

"Standard contracts range from three to five years, but can be extended,indefinitely, depending on the worker's performance and loyalty, " Scarlatoiu said.

The softer language also allows North Koreans to work overseas for "humanitarian purposes," which are ill-defined.

But even if all the North Korean laborers overseas are sent home, there is concern over what awaits them in the totalitarian state.

Under a normal reintegration plan with a known number of citizens returning, former workers are placed under strict surveillance for three years, according to North Korean defectors interviewed by Scarlatoiu.

"Despite the fact that they may have been in the dormitories for most of their time, they have certainly sensed freedom, seen things that they probably did not see in their country," said Jae H. Ku, director of the U.S.-Korea Institute at Johns Hopkins University.

"If that becomes an issue, what would the regime decide to do with these tens of thousands of workers who come back?"

For now, North Koreans around the world are still making money for the regime.

And as long as they're toiling overseas, Kim Seung-chul will continue his mission to expose the poor working conditions.

"I hope that one day they'll receive fair pay and live like human beings," he said.

Joyce S. Lee contributed to this report.

Read more:

How Russia quietly undercuts sanctions intended to stop North Korea’s nuclear program

UAE stops issuing new visas for North Korean laborers

U.N. agrees to toughest-ever sanctions against North Korea

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