米国が1938年1月11日には南京での日本軍による中国軍捕虜に対する大量処刑を把握していたという記録

The Ambassador in China (Johnson) to the Secretary of State
Hankow, January 11, 1938—2 p.m.
[Received January 11—12:10 p.m.]

I am even convinced that the action of Japanese soldiers at Nanking who carried out mass executions of Chinese soldiers that had given up their arms to certain foreigners of the committee which organized the safety zone for noncombatants, was partly motivated by a desire to convince the Chinese that they must not depend upon white intervention in their opinions. We appear to face a group of young Japanese ronin who tolerate no control from Tokyo and who will be found to be recklessly contemptuous of any adverse effect which their actions in China may have upon Japan’s relations with Western Powers, in the belief that the rest of the world is not prepared to do more than register a protest against violation of treaties relating to the Far East and to the rights and interests of third powers.

https://history.state.gov/historicaldocuments/frus1938v03/d13