TOKYO — Last summer, Halmat Rozi, a Uyghur Muslim living in Japan, received a video call from his brother in China’s western Xinjiang region. His brother said he had someone he wanted Mr. Rozi to meet: a Chinese security officer.China’s top leader, Xi Jinping, had been invited to Japan, and the officer had some questions. Were Mr. Rozi and his fellow Uyghur activists planning protests? Who were the group’s leaders? What work were they doing? If Mr. Rozi cooperated, his family in China would be well cared for, the officer assured him on a second video call. …
