In a courtroom in Zharkent, Kazakhstan, in July 2018, a former kindergarten principal named Sayragul Sauytbay calmly described what Chinese officials continue to deny: a vast new gulag of “de-extremification training centers” has been created for Turkic Muslim inhabitants of Xinjiang, the Alaska-sized region in western China. Sauytbay, an ethnic Kazakh, had fled Xinjiang and was seeking asylum in Kazakhstan, where her husband and son are citizens. She told the court how she had been transferred the previous November from her school to a new job teaching Kazakh detainees in a supposed “training center.” “They call it a ‘political camp’…but in reality it’s a prison in the mountains,” she said. There were 2,500 inmates in the facility where she had worked for four months, and she knew of others. There may now be as many as 1,200 such camps in Xinjiang, imprisoning up to a million people, including Kazakhs, Kyrgyz, and especially Uighurs, who make up around 46 percent of Xinjiang’s population.

Sauytbay’s testimony provided the first dramatic public evidence from a Chinese citizen of the expanding gulag in Xinjiang. But news of it has been emerging since 2017, thanks to remarkable reporting by Gerry Shih (now at The Washington Post) for the Associated Press and Josh Chin, Clément Bürge, and Giulia Marchi for The Wall Street Journal, as well as important early stories from other researchers and correspondents, including Maya Wang (Human Rights Watch), Rob Schmitz (NPR), and Megha Rajagopalan (BuzzFeed News). Especially important is the Washington, D.C.–based Radio Free Asia Uighur service, which has for years provided detailed, accurate coverage despite notorious controls on information in Xinjiang.

At first, officials in the People’s Republic of China (PRC) denied there were any camps. Then state media briefly floated a story that 460,000 Uighurs from southern Xinjiang had been “relocated” to “jobs” elsewhere in the Xinjiang region. There have been no further announcements about that jobs program, and the explanation seems to have been dropped. When confronted at an August 2018 UN hearing by Gay McDougal, a member of the UN Committee on the Elimination of Racial Discrimination, the Chinese delegation denied that there were any “reeducation” camps, while admitting that there were “vocational education and employment training centers” and other “measures” to counter “extremism.” When pressed again at the UN Human Rights Council’s universal periodic review in November 2018, the PRC representative accused “a few countries” of “politically driven accusations” and repeated that the camps were simply providing vocational training to combat extremism.

People outside Xinjiang first began to learn about the camps in 2017. Uighurs abroad grew alarmed as friends and relatives at home dropped out of touch, first deleting phone and social media contacts and then…