On the morning of May 21, 1938, thirty people died within roughly an hour in Kaio, a small community in Nishikamo village, a mountain district of Okayama Prefecture that is now part of the city of Tsuyama. The deaths are attributed to Mutsuo Toi, a 22-year-old man from the same community, who died by suicide that morning. He left written notes. Because he was dead before any arrest could be made, no one was charged, no trial was held and no court made a finding. The police inquiry was opened and then closed within days.
In Japanese the case is called the Tsuyama thirty-person killings, after the nearest town. It was a single event of one night, and it ranks among the deadliest episodes of its kind in the country's modern history.
Kaio lay in the hills near the border between Okayama and Tottori prefectures, in the district then known as Nishikamo village. It was a farming settlement, and in May its households were busy with raising silkworms. About 111 people lived in the hamlet, so the dead amounted to roughly a third of its residents.
Toi was 22 and had grown up in the community. Later accounts of how the village treated him are interpretations written decades afterward, and no court weighed them.
The killings took place in the early hours and were over in about an hour. Thirty residents of Kaio and of the neighboring Sakamoto area died. They ranged widely in age and included both men and women, and some families lost several members.
He died by suicide that morning. The notes he left were written before the events and shortly before his death.
Police opened an inquiry into the thirty deaths. With the suspect dead, it was closed without a formal conclusion on the questions a trial would have tested. On May 23, 1938, two days after the events, prosecutors announced that they would not seek an indictment because the suspect had died.
There is therefore no indictment, no verdict, no sentence and no appeal in this case. Toi was never before a court at any stage, and the legal status of the deaths attributed to him is that they are attributed, uncharged and unadjudicated.
The case was on the front pages of national newspapers at the time, even though Japan was then engaged in the Second Sino-Japanese War.
Within Kaio, surviving relatives of the dead mostly stayed in the area, and farmland left without owners was divided among those who remained. The episode was treated for decades as a subject the community did not discuss.
The police report on the case was withheld from public view for many years after the war. In the 1970s and 1980s two widely read books became the main public accounts, and later researchers found that parts of one of them were invented. A copy of the official report was later traced to a university library in the United States and used for a 2024 book-length reconstruction. Later films and novels have drawn on the events; they are fiction.
The count is thirty dead. The cause of the events, and the weight to give to the community's treatment of Toi and his personal circumstances, are matters of interpretation, because no court heard evidence.
May 21, 1938, early hours: thirty residents of Kaio and Sakamoto, in Nishikamo village, die within about an hour.
May 21, 1938, morning: Toi dies by suicide.
May 23, 1938: prosecutors announce they will not seek an indictment because the suspect has died.
1970s to 1980s: two widely read books become the main public accounts of the case.
2024: a new book-length reconstruction is published, drawing on a copy of the police report.