BERLIN — Many people around the world may just now be learning that around a million Uighur Muslims and other minorities have been locked up in extrajudicial internment camps in the region of Xinjiang, in western China. There is a reason for that: Xinjiang is remote and the Chinese government has expended considerable effort to keep the news hidden, from harassing foreign journalists to seizing family members of activists to censoring information within its own borders.

Herbert Diess, however, should have no excuse.

Mr. Diess is the chief executive of Volkswagen, which opened a plant in Xinjiang in 2013 that employs almost 700 local workers and can make up to 50,000 cars a year. In an interview with the BBC in April, Mr. Diess said he was not aware of the system of camps or the Muslim minorities subject to mass detention, even though his company’s factory is within a 90-minute drive from four such detention centers. (The company issued a new statement saying it did, in fact, know about the treatment of Uighurs in Xinjiang and was committed to human rights.)

What excuse do the other chief executives and board presidents use?

I have found that about half of the largest 150 European companies had some presence in Xinjiang, an area that Amnesty International has described as “an open-air prison.” Their investments merit far more scrutiny from both regulators and the public, and European governments need to form standards for companies dealing with Xinjiang.

At the top of the list of companies that deserve a thorough review is Siemens. This large German conglomerate collaborates on advanced technologies in automation, digitization and networking with China Electronics Technology Group Corporation, a state-owned military contractor that has developed a policing app used in Xinjiang that, according to Human Rights Watch, has led some people to be sent to the camps.