Grose starting hunting down evidence in the spring. Step one was running a search for “reeducation center” using Baidu, the Chinese equivalent of Google. He said that led him to news reports that described how local officials, under a policy known as qu jiduanhua gongzuo (“de-extremification work”), were “reeducating” Muslim ethnic minorities—notably Uighurs and Kazakhs—in the northwestern Xinjiang region, which Beijing has long viewed as a breeding ground for extremism and separatism. Step two was using that policy’s name as a search term in Baidu, which he said led him to government websites. Step three was seeing what those websites said about the centers’ activities and locations.

Using this simple process, Grose said he found photos of a ribbon-cutting ceremony at a recently built facility in Xinjiang, along with a local government press release. “They have officials standing in front of a gate, and the gate quite clearly says in Chinese and Uighur ‘reeducation center,’” he said. “So there we have physical proof.” After finding photos like this or other documentation, Grose would save the material as PDFs or upload them to the digital archive known as the Wayback Machine, and post the contents on Twitter.