Short answers, pulled from the story.
The Nanjing Massacre began on the 13th of December 1937, when Japanese troops entered the Chinese capital. Traditional historiography dates it as unfolding over six weeks, but atrocities in the Nanjing area persisted until late March 1938, ending with the establishment of the collaborating weixin zhengfu government on the 28th of March 1938.
Estimates of the death toll vary widely. The International Military Tribunal for the Far East estimated more than 200,000 killed. Newer estimates range from 100,000 to 200,000. Other figures range from a low of 40,000, confined to the city itself, to a high of over 340,000 encompassing the entire Shanghai-Nanjing region.
John Rabe was a German businessman and Nazi Party member living in Nanjing who was elected leader of the International Committee for the Nanking Safety Zone. His Nazi Party membership gave him standing with the Japanese forces under the German-Japanese Anti-Comintern Pact. The Safety Zone he helped establish is credited with saving between 200,000 and 250,000 Chinese lives, and his diaries are among the most detailed firsthand records of the massacre.
Prince Yasuhiko Asaka, installed as temporary commander, issued an order to "kill all captives" before the city's capture. He arrived at the front on the 8th of December 1937, after preliminary negotiations suggested the Chinese garrison might surrender. After the war, Asaka was granted immunity from prosecution as a member of the imperial family and was never tried.
The Nanking Safety Zone was an area in the western quarter of Nanjing demarcated with Red Cross flags, established on the 22nd of November 1937 by a 15-person International Committee of Western residents. It is credited with saving at least 200,000 lives. The Safety Zone was forcibly renamed the Nanjing International Rescue Committee on the 18th of February 1938, and its last refugee camps closed in May 1938.
Between the ceasefire announcement on the 15th of August 1945 and the arrival of American troops on the 28th of August, Japanese military and civil authorities systematically destroyed military, naval, and government archives. Imperial General Headquarters dispatched enciphered orders to field commands across the Pacific and East Asia to burn incriminating evidence. Professor Tanaka Hiromi estimated that less than 0.1 percent of the material ordered destroyed survived, and Japan's director of Military History Archives confirmed in 2003 that approximately 70 percent of wartime records were destroyed.