Autism, Murder and the Death Penalty: Two Japanese Cases

Can autism ever reduce criminal responsibility for murder?

It is an uncomfortable question, but one that courts occasionally have to answer. A recent paper by Kashiwagi and Hirabayashi (2026)[1] examines two extraordinary Japanese cases in which healthcare professionals with ASD or autistic traits committed multiple homicides. Although the defendants shared certain autistic characteristics, the courts reached dramatically different conclusions: one was sentenced to death, while the other received indefinite imprisonment.

The authors place these cases within the broader debate about mental disorders, criminal responsibility and capital punishment. In 2023, the World Psychiatric Association declared that people with mental illness or intellectual and developmental disabilities should not be executed. Nevertheless, Japanese courts have continued to uphold death sentences in some cases involving defendants diagnosed with psychiatric or neurodevelopmental conditions.[2]

Before examining the cases, one point deserves emphasis. There is no evidence that autistic people are more likely to commit violent crime than the general population. On the contrary, they are far more often victims than perpetrators. However, rare and shocking crimes inevitably attract enormous public attention—especially when the offenders are healthcare professionals entrusted with the care of vulnerable patients.

Case 1: The Caregiver

The first defendant was a man in his twenties employed as a caregiver in a nursing home. Over a period of two months, he killed three residents by throwing them from fourth- and sixth-floor balconies. Remarkably, after each killing he attempted cardiopulmonary resuscitation (CPR).

The court heard that he had long been fascinated by emergency medicine and chest compressions and regarded this obsessive interest as part of the motive for his crimes. He was also experiencing considerable workplace stress, had been subjected to verbal abuse and physical aggression, and was reminded of childhood trauma involving his father threatening him with a knife.

He was diagnosed with ASD according to DSM-5 criteria. Although his IQ was 68, his educational achievements and qualification as an emergency medical technician meant that he did not meet the criteria for intellectual disability.

The court accepted that certain autistic characteristics—including difficulty coping with unexpected events, heightened sensitivity to verbal aggression and restricted, obsessive interests—had influenced his behaviour. However, it concluded that these factors did not substantially impair his criminal responsibility.

The judges pointed to extensive evidence of planning and purposeful intent. He monitored the movements of colleagues, concealed evidence and created false records to make the deaths appear to be suicides. These actions demonstrated that he understood the wrongfulness of what he was doing and was capable of controlling his behaviour.

The judgment described the murders as exceptionally cruel, stating that he threw elderly residents "as if throwing objects." His refusal to accept responsibility, repeated fabrication of excuses and apparent lack of remorse convinced the court that rehabilitation had not even begun. Finding few mitigating circumstances, it imposed the death penalty.

Case 2: The Nurse

The second defendant was a nurse in her thirties who murdered three patients by injecting benzalkonium chloride into intravenous drips and attempted to poison four others.

Unlike the first case, her crimes were driven by overwhelming anxiety rather than fascination. She had previously experienced situations in which families blamed her when patients deteriorated unexpectedly. At her current hospital she witnessed another nurse being harshly criticised following a patient's sudden death. Terrified that she would one day face similar confrontations, she developed a catastrophic solution: if patients died while she was not responsible for them, she would never have to deal with grieving relatives.

She displayed autistic traits and was also experiencing depressive symptoms. However, after extensive assessment—including interviews, school records and psychological testing—the evaluator concluded that she did not meet DSM-5 criteria for either ASD or depressive disorder.

Nevertheless, the court accepted that her autistic characteristics and depressed state had narrowed her thinking and contributed to an extremely rigid, simplistic style of problem-solving. Within this distorted reasoning, killing patients came to appear as the only way to reduce her anxiety. These factors were therefore treated as partially mitigating.

Even so, the court concluded that she had acted deliberately. She selected a method that would cause deaths during shifts when she would not have to deal with families, used her professional knowledge to minimise suspicion and clearly understood that her actions were illegal. Consequently, neither her autistic traits nor her psychological state substantially impaired her ability to understand the wrongfulness of her actions or to control her behaviour.

The seriousness of the crimes remained overwhelming. The court emphasised the grave danger to life, the calculated abuse of professional trust and the defendant's entirely self-centred motive.

However, one important difference separated this case from the first. Throughout the proceedings, she expressed genuine remorse, openly acknowledged painful memories and stated, "I want to atone by dying." The judges concluded that, despite the gravity of her offences, she retained the potential for rehabilitation. She was therefore sentenced to indefinite imprisonment rather than death.

Why These Cases Matter

The contrast between these two cases illustrates an important legal principle. An autism diagnosis does not automatically reduce criminal responsibility. Courts are concerned not simply with diagnosis, but with whether the defendant's condition significantly impaired their ability to understand the wrongfulness of their actions or to control their behaviour.

Both defendants displayed autistic characteristics. Both committed multiple murders. Yet the courts ultimately focused on very different issues: the degree of planning, awareness of wrongdoing, motive, concealment of the crimes, and—perhaps most strikingly—the defendants' attitudes after the offences.

These cases also serve as a reminder that sensational crimes involving autistic individuals are extraordinarily rare. They should not be used to reinforce stereotypes about autism and violence. Instead, they demonstrate the complexity of assessing criminal responsibility when neurodevelopmental conditions intersect with extreme criminal behaviour.

__________________  

[1] Kashiwagi H, Hirabayashi N. (2026). Case Report: Death penalty versus indefinite imprisonment in Japan: a case note of two court judgments involving autism spectrum disorder and autistic traits. Frontiers in Psychiatry. doi:10.3389/fpsyt.2025.1690300.

[2] In Japan, criminal responsibility is evaluated according to two components: (i) the capacity to appreciate the rightfulness or wrongfulness of one’s actions (cognitive capacity), and (ii) the capacity to act in accordance with such appreciation (volitional capacity). Full responsibility is recognised when both capacities are preserved. Diminished responsibility is found when either capacity is markedly impaired. Legal insanity is determined when either capacity is lost.