Verifying facts is what journalists are supposed to do. But because the atrocity in Nanjing during the Sino-Japanese War has become a cornerstone of Chinese nationalism, and thus of the Communist Party of China’s propaganda, any critical scrutiny of what precisely happened is seen as criticism of the Chinese government.
Perhaps this needs some explanation. Until the death of Mao Zedong in 1976, official Chinese accounts paid little attention to the Nanjing Massacre. History under Mao was instead a heroic tale of communist victory over fascist and bourgeois oppressors. Nanjing had been the Chinese Nationalist capital at the time of the Sino-Japanese War. The massacre was thus a story of Nationalist defeat, not communist heroism.