Ayumi Kuboki, a nurse, worked at a hospital in Yokohama when three elderly inpatients died there in September 2016. In November 2021 the Yokohama District Court, sitting with lay judges, found all the charged facts proven and sentenced her to life imprisonment. Prosecutors had asked for the death penalty. On June 19, 2024 the Tokyo High Court dismissed appeals from both the prosecution and the defense and left the sentence in place.
The three people named in the indictment were Asae Okitsu, 78, Sozo Nishikawa, 88, and Nobuo Yamaki, 88. They were among 48 patients who died at the hospital between July 2016 and the point when the case came to light, a number on which the courts made no finding beyond the three deaths on trial. Kuboki herself spoke of a larger number of victims during questioning, but those statements were not tested in court and she did not repeat them at trial.
The hospital stood in Kanagawa Ward, in the city of Yokohama. From July 2016 an unusual number of its inpatients died. By the time the matter was treated as a criminal case, 48 patients had died in a period of roughly three months. Charges were brought in only three of them.
The first of the three deaths to draw attention was that of Nobuo Yamaki, 88, on September 20, 2016. His death was treated as suspicious. The deaths of Asae Okitsu, 78, and Sozo Nishikawa, 88, also fell in September 2016, and all three were later charged as murders. Kuboki worked on the ward where they were patients.
For nearly two years the case had no suspect in custody. Kuboki was questioned by the Kanagawa Prefectural Police on a voluntary basis. At first she denied involvement. On June 30, 2018, during her second voluntary interview, she admitted what she had done. Police arrested her on July 7, 2018, and prosecutors indicted her on December 7, 2018.
Before the indictment, a psychiatrist working for the prosecution diagnosed mild autism spectrum disorder and took the position that she had full criminal responsibility. The question of her mental state became the main contest at trial.
Kuboki was charged with murder in the deaths of the three patients and with preparation for murder in connection with other patients. At the first hearing on October 1, 2021 she told the court that the charges were correct in every respect. The defense did not dispute the facts. It argued that she had been in a state of diminished capacity, and her lawyers pointed to schizophrenia in support of a reduced sentence. Prosecutors said she had full criminal responsibility.
The lay-judge trial opened on October 1, 2021 at the Yokohama District Court and ran until October 22. On October 11, the fifth hearing, Kuboki was questioned and spoke of her regret for the killings. She told the court that she had not wanted relatives of patients to blame her for problems on her shifts. The prosecution put its case in similar terms: that her motive was a reluctance to deal with the families of patients who died.
On October 22 the prosecution asked for the death penalty. The defense argued that life imprisonment was the right sentence. In her final statement Kuboki apologized and said she wanted to atone.
On November 9, 2021 the Yokohama District Court sentenced Kuboki to life imprisonment. The court found that she had full criminal responsibility and that all the charged facts had been proven. It also found the crimes were planned. It nevertheless declined to impose the death penalty, citing her admission of the charges and her apology to the families of the victims, and said she should be given the chance to walk the path of rehabilitation.
The prosecution appealed against the sentence as too lenient, and the defense appealed as well; by December 20, 2021 the case had moved to the Tokyo High Court, where the central issue was whether the sentence was appropriate. The prosecution sought the death penalty. The defense argued that the District Court had been wrong to find full criminal responsibility.
On June 19, 2024 the Tokyo High Court dismissed both appeals. It upheld the life sentence, found nothing unreasonable in the first ruling and noted her autism spectrum traits as a factor in her mental state. The court also found no error in the District Court's assessment of her motive and her prospects of rehabilitation.
After the High Court ruling of June 19, 2024 Kuboki's sentence of life imprisonment stood. Whether either side took the case to the Supreme Court, and whether the sentence has become final, is not on record. Her place of custody is not on record.
Since 2009, serious criminal cases in Japan, including murder, have been tried in the district courts by panels that combine professional judges and citizens chosen as lay judges. Kuboki's trial was held in that form. Prosecution and defense may both appeal a district court sentence to a high court, and the Supreme Court is the court for further appeal. In this case the penalty options at first instance were the death penalty, which the prosecution sought, and life imprisonment, which the court imposed.
The number of victims is not settled. The hospital recorded 48 deaths among inpatients from July 2016, and only three were charged. In police questioning Kuboki spoke of involvement in about 20 deaths, and in a psychiatric evaluation she said the number could be more than 40. These are her own statements, they led to no further charges, and the courts made no findings on them. Those further deaths are suspected and not charged.
The question of mental state was disputed and decided: the defense claimed diminished capacity and the courts, at both levels, found that she had full criminal responsibility.
July 2016: deaths among inpatients at the hospital in Yokohama begin to rise; 48 patients die by the time the case comes to light.
September 2016: the three patients named in the indictment die; Nobuo Yamaki dies on September 20.
June 30, 2018: Kuboki admits the offenses during voluntary questioning.
July 7, 2018: she is arrested by the Kanagawa Prefectural Police.
December 7, 2018: she is indicted.
October 1, 2021: the lay-judge trial opens at the Yokohama District Court.
October 22, 2021: prosecutors seek the death penalty.
November 9, 2021: life imprisonment.
December 20, 2021: both sides' appeals are before the Tokyo High Court.
June 19, 2024: the Tokyo High Court dismisses both appeals and upholds the sentence.