(CNN) -- Living at the China-North Korea border, I had the unique opportunity to train under two North Korean tae kwon do masters. While I told people I was there to learn the rare North Korean martial art from some of their best instructors, I was secretly helping North Korean refugees on the 6,000-mile modern-day underground railroad from the Hermit Kingdom to South Korea, for food and a better life. In 2004, I traveled to North Korea to see the country, even though many people warned me not to take the risk. One of our detained Chinese workers later said that North Korea had a file on me, but did not know my name. I lived with the fear of being detained, abducted or assassinated by the North Korean government for many years. Whenever I hear of another American detained, it reminds me of that anxiety.
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Mike Kim helped North Koreans escape at China border, lived with fear of being kidnapped
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He says interview with American citizens was move to get high-ranking U.S. official to visit
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Kim: Regime wants to impress its people with message "Look at how powerful we are"
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Kim: North Korea walking a fine line: The world is sick of its games, its people wising up
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@placeholder has been collecting American citizens and planning for this very moment.
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How North Korea may be using @placeholder detainees as 'bargaining chips'
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It wants to use the three @placeholder as bait but not anger the United States so much that a high-ranking envoy will not come to the negotiating table.
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Phones connected to @placeholder cell towers are being used along the border to relay messages in and out of the country.