SEOUL, South Korea — He was the poster boy for human rights atrocities in North Korea; a soft-spoken survivor of the North’s cruel gulags who eventually met such dignitaries as John Kerry in his campaign to focus attention on the North’s abuses. His harrowing tales of life in a prison camp — including being forced to watch his mother and brother being executed — stunned even those steeped in defectors’ stories and made him a star witness for an unprecedented United Nations’ investigation of abuses by the North’s rulers.

Now, that survivor, Shin Dong-hyuk, is retracting central facts of his life story, memorialized in a 2012 book, “Escape from Camp 14,” by a former Washington Post reporter that has been published in 27 languages.

Mr. Shin, who gives his age as 32, now says that the key fact that set him apart from other defectors — that he and his family had been incarcerated at a prison that no one expected to leave alive — was only partly true, and that he actually served most of his time in the less brutal Camp 18. He also said that the torture he endured as a teenager, instead happened years later and was meted out for very different reasons.

Mr. Shin’s confession has raised fears among other prison camp survivors and South Korean human rights activists that it could stall an already difficult campaign by the United States and other nations to get the Security Council to push for an investigation at the International Criminal Court. Other camp survivors also testified before the United Nations investigators, recounting being tortured and starved, but activists worry that Mr. Shin’s recanting will help China and other North Korea supporters fight against opening a court case.