The late "Great Leader" Kim Il-sung reportedly viewed him as a valuable N. Korean asset in Europe. Song was playing a honest "dissident" while surreptitiously feeding N. Korean lines to Koreans in Europe.
The former N. Korean diplomat mentioned in the article was assigned as Song's handler while posted at the N. Korean interest section in E. Berlin. He later defected to U.S., bringing with him large quantities of documents. It is some of these documents which provided conclusive evidences to his connection with N. Korea. One of them is about changing his code name, Kim Chul-soo, after Mr. Hwang Jang-yop outed him in S. Korean presses several years ago, saying that Kim Chul-soo is actually Song Du-yul's code-name. At the time, Song had the nerve to brint suit against Mr. Hwang for defamation in S. Korean court.