After the Japanese surrender, he was tried and convicted in British Singapore as a war criminal for his role in the Sook Ching massacres.

Nishimura served as presiding judge at the court-martial of army officers responsible for the assassination of Prime Minister Inukai Tsuyoshi in 1932.

During the Battle of Muar, the Imperial Guards killed 155 Australian and Indian prisoners of war in an event known as the Parit Sulong Massacre.

Nishimura himself was often at odds with the commander of the 25th Army, General Tomoyuki Yamashita, at times engaging in conduct that seemed deliberately insulting.

From February 1944, Nishimura was appointed Japanese military Governor of Sumatra, a post he held until the end of the war.

After the end of the war, Nishimura was tried by a British military tribunal in Singapore for the events related to the Sook Ching massacre.

[4][5] Ward also claimed that Godwin took no action on the testimony of Lieutenant Fujita Seizaburo, who reportedly stated that he was directly responsible for the Parit Sulong massacre.