Ikuya Hatakeyama was born around 1944 in Japan. His early life was marked by instability after the death of his mother during his childhood. Following her death, Hatakeyama was raised by his aunt. Despite these circumstances, he was regarded as a diligent and capable student. He performed well academically and graduated from an agricultural high school, after which he successfully passed the national civil service examination administered by the Ministry of Construction.

Hatakeyama began his professional career working for construction offices in Kōchi and later Iyo‑Mishima. Colleagues described him as quiet and reserved, with noticeable difficulty forming social connections. Over time, his mental health deteriorated. In 1972, Hatakeyama was admitted to a psychiatric institution after exhibiting signs of emotional instability. He was diagnosed with depression, and as a result of his condition, the Ministry of Construction retired him from civil service.

Hatakeyama remained hospitalized for treatment and was discharged approximately three months before the shooting. After leaving the hospital, he obtained employment at a toothpick factory in Ioki, attempting to reintegrate into civilian life. During this period, there is no documented evidence of prior violent behavior toward others, though he legally purchased a 12‑gauge shotgun and approximately 100 rounds of ammunition around eight months before the attack.

At approximately 8:40 p.m. on 6 November 1975, Ikuya Hatakeyama exited his home in Aki, Kōchi Prefecture, carrying his 12‑gauge shotgun. He stepped onto the street and began shouting incoherently at a nearby neighbor, who was the principal of the local junior high school. Without warning, Hatakeyama opened fire, initiating a shooting spree that would become one of the deadliest mass shootings in Japanese history.

After the initial attack, Hatakeyama entered a neighboring residence where he shot Hiromichi Ushimade, a 46‑year‑old man, killing him at the scene. Ushimade’s 27‑year‑old wife, Kimiko, was critically wounded. Their son, hearing the gunshots, ran downstairs and immediately contacted the police. Hatakeyama then moved on to another nearby home, where he fatally shot a 27‑year‑old woman and her young daughter.

Continuing through the neighborhood, Hatakeyama entered two additional houses. In these attacks, he killed a 51‑year‑old man and a 58‑year‑old woman, mortally wounded a 51‑year‑old woman, and seriously injured another resident. By the end of the rampage, Hatakeyama had fired more than a dozen rounds, leaving six people dead and two critically injured.

The gunfire alerted nearby residents, who rushed toward Hatakeyama and managed to disarm him. Despite being subdued momentarily, Hatakeyama escaped the scene before police arrived.

The Kōchi Prefectural Police launched a large‑scale manhunt, assisted by members of the local fire brigade. Hatakeyama evaded capture overnight and was discovered hiding on a hill behind a park, approximately two kilometers from the crime scene. He was arrested shortly after 11:00 p.m. on 7 November 1975, roughly one day after the shooting.

The Aki shooting was widely reported as the deadliest mass shooting in Japan since the 1938 Tsuyama massacre, drawing national attention and prompting renewed scrutiny of gun ownership regulations and mental health oversight.

During police interrogation, Hatakeyama stated that he carried out the shooting because he was severely depressed and had an overwhelming desire to kill people. He told investigators that he bore no personal resentment toward his victims and that their identities were irrelevant to him at the time of the attack.

At trial, prosecutors acknowledged that Hatakeyama was suffering from mental health issues but argued that he retained sufficient awareness of his actions and should therefore be held criminally responsible. However, three psychologists testified that Hatakeyama was suffering from schizophrenia and paranoia and concluded that he was legally insane at the time of the shooting. Based on this assessment, Hatakeyama was acquitted by reason of insanity in September 1981.

The prosecution appealed the verdict, and a retrial was ordered. On 4 December 1984, Hatakeyama was found criminally responsible and sentenced to life imprisonment. This ruling was final, and no further appeals were permitted.