The Tsuyama massacre, known in Japan as the Tsuyama jiken (津山事件), remains one of the most horrific mass killings in the nation’s history. On the night of May 21, 1938, 21-year-old Mutsuo Toi unleashed a brutal attack on the rural village of Kamo, near Tsuyama in Okayama Prefecture. Armed with a modified shotgun, a katana, daggers, and an axe, he killed 30 people—including his own grandmother—and seriously injured three others before taking his own life. To this day, it stands as the deadliest shooting carried out by a single gunman in Japan.
Background
Kamo at the time was a secluded farming community of just 23 households and around 111 residents. Like many rural Japanese settlements of the era, it was insular, with long-standing local relationships and few newcomers. Over the decades, the village was gradually absorbed into larger surrounding municipalities due to depopulation, but in 1938 it remained a tight-knit—and ultimately vulnerable—community.
The Perpetrator: Mutsuo Toi
Mutsuo Toi was born on March 5, 1917, in Okayama’s Tomata District. Orphaned early by tuberculosis, he and his sister were raised by their strict grandmother, who limited their social interactions. Toi excelled in primary school and was initially outgoing, but his development took a downturn when he was denied further education and his sister married out of the household when he was 17. Social withdrawal soon followed.
In his late teens, Toi developed health problems, including pleurisy, which prevented him from doing agricultural work. He drifted academically, became fascinated by sensational crime stories—particularly the case of Sada Abe—and even attempted writing a novel titled Yūtokaiōmaru. He also engaged in yobai, or “night-crawling,” an illicit local custom involving young men secretly entering women’s bedrooms in hopes of sexual encounters.
A turning point occurred in 1937, when Toi reported for military conscription during the Second Sino-Japanese War. Diagnosed with tuberculosis—a feared and incurable disease at the time—he was declared unfit for service. Soon after, the women with whom he had previously had premarital relationships began distancing themselves. This rejection, combined with his illness, fed a growing sense of humiliation and resentment.
Toi had previously acquired a hunting license and firearms for pest control, but after an incident in which he attempted to administer medicine to his grandmother and was falsely suspected of poisoning her, police confiscated his weapons and revoked his license. Determined to rearm, he secretly acquired a second-hand Winchester Model 1897 shotgun, a katana, knives, and other weapons through private channels. He also modified his shotgun into a higher-capacity firearm that could hold nine shells instead of five.
Lead-up to the Massacre
The exact trigger for Toi’s rampage remains uncertain, but many historians believe the timing was not random. Two married former lovers had recently returned to the village to visit relatives, potentially provoking Toi’s anger. His suicide notes indicate a deep obsession with perceived slights, social rejection, and shame tied to his illness.
On May 20, the night before the killings, Toi cut the village’s power lines, plunging Kamo into darkness. The stage was set for what would become one of the most devastating mass murders in Japanese history.
The Massacre
At approximately 1:30 a.m. on May 21, 1938, Toi began his attack by killing his 76-year-old grandmother as she slept, decapitating her with an axe. He later wrote that he killed her to spare her the shame of being associated with a murderer.
Strapping two flashlights to his head, armed with his shotgun, katana, daggers, axe, and carrying 200 rounds of ammunition, Toi moved through the sleeping village. Using the familiarity gained from years of yobai, he entered home after home, targeting residents with ruthless precision. Many victims were shot; others were slashed or bludgeoned. The attack lasted roughly 90 minutes and left 29 villagers dead, two fatally wounded who later succumbed to their injuries, and three others seriously injured. Nearly half of the tiny village was wiped out.
By dawn, Toi retreated to a nearby mountain and ended his life by shooting himself in the chest.
Suicide Notes and Motive
Toi left behind several lengthy suicide notes. They offer critical insight into his mental state during the months leading up to the massacre. Central to his writings was the stigma of tuberculosis. In the 1930s, the disease carried profound social implications—fear of contagion, assumptions of weakness, and ostracism. Toi believed that once villagers learned of his diagnosis, they no longer saw him as a desirable young man but instead viewed him with disgust.
He also described feeling mocked and shamed for being “hypersexual,” a label he believed villagers used behind his back following his earlier romantic relationships and participation in yobai. Whether these judgments were real or perceived remains uncertain, but to Toi, they were deeply wounding.
His notes reveal a mixture of resentment, self-pity, and a desire for revenge. He wrote that he had been insulted, rejected, and pushed to the margins of village life. Killing his neighbors, he believed, was the only way to retaliate against the humiliation he felt. Yet he also expressed selective restraint: there were individuals he wished to kill but refrained from attacking because doing so would require harming innocent people nearby.
Aftermath and Legacy
The massacre shocked Japan and drew nationwide scrutiny. Newspapers of the time devoted extensive coverage to the killings, exploring Toi’s motives, weapon modifications, and the failure of authorities to recognize his growing danger. The case also sparked debate about mental health, social isolation, and rural customs such as yobai, which many urban readers viewed as archaic and troubling.
Long after the event, the Tsuyama massacre remains a grim landmark in Japanese criminal history—not only because of the sheer number of casualties but because it exposed underlying tensions within rural society. Toi’s blend of illness-related stigma, personal grievances, and access to weapons created a tragic convergence that devastated an entire community.
Today, the Tsuyama massacre is still studied as a case of extreme social alienation and remains the deadliest lone-gunman shooting Japan has ever experienced.
