Many countries are guilty
I think that Japan was not the only country responsible for killings, during a war casualties are inevitable, even killings of innocent (unfortunately), there are are other countries too which are responsible for world war 2 except Japan, Germany killed millions of people during world war 2 , and Stalins victims are tens of millions therefore blaming only Japan is something inacurate from the historical point of view.
Japanese Views on Nanjing/2nd Sino-Japanese War 1931-1945
Acknowledging Bob Tadashi Wakabayashi's research "The Nanking 100-Man Killing Contest Debate," Gregory Smits of Penn. State Univeristy states, "the sheer quantity, wide variety and high quality of evidence available today that attest to this massacre makes it more difficult than ever for anyone with intellectual integrity to dismiss or minimize it."
Japanese Views of the Second Sino-Japanese War:
Through the lens of the Nanjing Massacre and Events Connected with It by Gregory Smits
Above page with extensive, informative links was built as part of
Making Japan: Modern Japanese History at Penn. State Univ. by Gregory Smits
Other material in topics of histories of Japan and China to be found at main page
East Asian History Textbooks, Gregory Smits