China stands accused of a gruesome trade in human organs. It’s difficult to prove, because the victims’ bodies are disposed of and the only witnesses are the doctors, police and prison guards involved. Even so, the evidence supports a damning verdict.

The charge is that many prisoners of conscience—Falun Gong members, Uighur Muslims, Tibetan Buddhists and “underground” Christians—have been subjected to medical testing and had their organs forcibly removed. Those organs have fed an enormous trade in organ transplants.

Patients in China—including foreigners—are promised matching organs within days. Former Canadian politician and prosecutor David Kilgour, lawyer David Matas, American journalist Ethan Gutmann and a team of researchers have confirmed this by posing to Chinese hospitals as patients. Dr. Huang Jiefu, China’s former vice minister for health and chairman of its organ-transplant committee, ordered two spare livers as backups for a 2005 medical operation. They were delivered the next morning. In most advanced Western countries, patients wait months or even years for transplants.

In 2016 Messrs. Kilgour, Matas and Gutmann published a report, “Bloody Harvest/the Slaughter: An Update,” building on research that dates back to 2006. In this latest version, the authors estimated that between 60,000 and 100,000 organs are transplanted each year in Chinese hospitals.

Where are the organs coming from? China claims it has the “largest voluntary organ donation system in Asia” and stopped using prisoners in 2015. But the country has no tradition of voluntary organ donation.