structural:summarization
Evidence collection

The Japanese either destroyed or concealed important documents, severely reducing the amount of evidence available for confiscation. Between the declaration of a ceasefire on August 15, 1945, and the arrival of American troops in Japan on August 28, "the Japanese military and civil authorities systematically destroyed military, naval, andgovernment archives, much of which was from the period 1942–1945." Overseas troops in the Pacific and East Asia were ordered to destroy incriminating evidence of war crimes. Approximately 70 percent of the Japanese army's wartime records were destroyed. In regards to the Nanjing Massacre, Japanese authorities deliberately concealed wartime records, eluding confiscation from American authorities. Some of the concealed information was made public a few decades later. For example, a two-volume collection of military documents related to the Nanjing operations was published in 1989; and disturbing excerpts from Kesago Nakajima's diary, a commander at Nanjing, was published in the early 1980s.

During his time in China, Bernhard Arp Sindberg, an amateur photographer and friend to several foreign journalists, always had his camera with him, taking graphic photos of the civilian massacres and extensive destruction. Sindberg smuggled the unprocessed film out of China with the help of his company, and had entrusted the development of the film to his colleagues. After the war, he retrieved his photos, producing one of the few photographic records documenting the Nanjing massacre.

Ono Kenji, a chemical worker in Japan, curated a collection of wartime diaries from Japanese veterans who fought in the Battle of Nanking in 1937. In 1994, nearly 20 diaries in his collection were published, which became an important source of evidence for the massacre. Official war journals and diaries were also published by Kaikosha, an organization of retired Japanese military veterans.

In 1984, in an attempt to refute Japanese war crimes in Nanjing, Kaikosha, the Japanese Army Veterans Association, interviewed former Japanese soldiers who had served in the Nanjing area from 1937 to 1938. Instead of refuting the massacre, the interviewed veterans confirmed that a massacre had taken place and openly described and admitted to taking part in the atrocities. In 1985, the interviews were published in the association's magazine, Kaiko, along with an admission and apology that read, "Whatever the severity of war or special circumstances of war psychology, we just lose words faced with this mass illegal killing. As those who are related to the prewar military, we simply apologize deeply to the people of China. It was truly a regrettable act of barbarity."

In early 1980s, after interviewing Chinese survivors and reviewing Japanese records, Japanese journalist Honda Katsuichi concluded that the Nanjing Massacre was not an isolated case, and that Japanese atrocities against the Chinese were common throughout the Lower Yangtze River since the battle of Shanghai. The diaries of other Japanese combatants and medics who fought in China have corroborated his conclusions.