Tashpolat Tiyip, president of Xinjiang University and one of China’s best-known geographers, was last seen at a Beijing airport in spring 2017 on his way to the opening of a research center in Germany. On that day he disappeared without a trace. A few months later, his wife Venira of 37 years, a college professor, learned that Tiyip was kidnapped by Chinese security forces and secretly tried as a “two-faced” Uighur separatist who has “poisoned the minds” of his students. He was sentenced to death with a two-year reprieve that expires about now. Over a thousand geographers from 50 countries signed a letter to Chinese President Xi Jinping asking him to halt the execution.

Tiyip was born in the Xinjiang Uighur region of China, attended a school, and worked as a tractor driver before enrolling in the geography program at Xinjiang University. Upon graduation he worked as an instructor for five years and then entered a doctoral program at the University of Tokyo, where he earned Ph.D. in applied geography. In 1993 he returned to his alma mater, became chairman of the geography department, and eventually rose to become university president in 2010.

Tiyip’s work on satellite sensing of ecosystems brought him international prominence. A charismatic leader with powerful intellect and enormous energy, and fluent in a number of foreign languages, he built close ties with numerous universities throughout the world. His students and colleagues were stunned by the news of his arrest and death sentence. According to them, Tiyip has never shown any disloyalty toward China.

Many believe that he became a victim of his high visibility at the time when China wanted to erase any reference to Uighur culture. A Uighur rising from a tractor driver to the Doctor Honoris Causa of Sorbonne in Paris was more than the government could swallow. He shared the fate of hundreds of Uighur intellectuals that disappeared in recent years.

Economics professor Ilham Tohti was sentenced to life in prison in 2014. This year he has been nominated for the Nobel Peace Prize by a bipartisan group of U.S. lawmakers. In December 2017, anthropology professor Rahile Dawut was snatched by security forces from a train to Beijing. She has not been heard from ever since. In January 2018, security forces raided the home of literature professor Abdulqadir Jalaleddin and took him to an undisclosed location with a hood over his head.

These cases represent the tip of the iceberg.

About 11 million Uighurs belonging to ethnic Muslim minority live in the western Xinjiang region. After China granted it an autonomous status in 1955, the government grew increasingly intolerant toward Uighur culture and language. In recent years it has shown determination to get rid of those who it views as beacons of Uighur identity and to reeducate the rest. Since 2015, China has been compiling a massive DNA database with a focus on its Muslim citizens. High resolution cameras have been installed in public areas and connected to supercomputers that use artificial intelligence for facial recognition of Uighurs to track their movement.

As many as 2 million Uighurs, close to 20% of their population, may have been detained in the internment camps. China denied the existence of such camps until 2018, finally succumbing to satellite images. It calls them reeducation camps. People have been detained in these camps indefinitely, women permanently separated from men, children from adults. A handful of inmates that managed to get out tell horror stories of torture and death. The scale of it brings Nazi concentration camps to mind.

Uighur American academic Elnigar Iltebir has been recently appointed by the Trump administration to the National Security Council. Chinese leaders must get the message, release Uighur academics, and close “reeducation” camps. If in doubt, reading about the Nuremberg trials may help.

Eugene M. Chudnovsky is a distinguished professor at the City University of New York and chairman of the Committee of Concerned Scientists.