Dai Toa Senso sakusen nisshi

Dating from 1940, the so-called Imoto diary was written by Imoto Kumao. Imoto Kumao was a high ranking military official in the Japanese headquarters in Nanjing. From 1940-1942 he was responsible to keep contact with the biological warfare Unit 731 in Ping Fan. His working diary contains a reference to the plague attack on Quzhou on 4 October 1940. The Imoto diary was uncovered by a Japanese historian in the early 1990s, but when he published his findings, the Japanese government classified the document.
Reference: http://www.sunshine-project.org/pingfan/pf9.html