What happened
Late on June 27, 1994, a toxic nerve agent was released in a residential area of Matsumoto, Nagano Prefecture. Residents became seriously ill and several died. Contemporary court reports initially counted seven deaths; later official and retrospective accounts record eight people killed after another victim died from long-term injuries.
The attack predated the better-known Tokyo subway sarin attack by roughly nine months. The two were separate criminal events and are documented separately on Crime by Region.
An innocent resident was treated as a suspect
One of the most important investigative failures involved Yoshiyuki Kono, whose wife was critically injured. Because chemicals were found at his home and he was the first person to report the incident, early police attention and intense media coverage focused on him. He was not the perpetrator. Evidence later established that Aum Shinrikyo was responsible.
Kono's treatment became a major example in Japan of the harm caused when suspicion hardens into public guilt before evidence has been tested. This page therefore distinguishes investigative suspicion from criminal responsibility.
Aum Shinrikyo and the court record
Subsequent prosecutions established that senior Aum figures planned and carried out the Matsumoto attack. Court reporting records convictions of multiple members for roles ranging from participation at the scene to producing the sarin used in the attack.
Noboru Nakamura, for example, was convicted of conspiring with Aum founder Shoko Asahara in the Matsumoto attack; the Tokyo High Court upheld his life sentence in 2003. Yasuo Hayashi received a death sentence for crimes that included his role in Matsumoto and the later Tokyo subway attack. Masami Tsuchiya was convicted for producing sarin used in the two attacks.
Asahara and final accountability
Shoko Asahara, whose legal name was Chizuo Matsumoto, was convicted in a broader case covering numerous Aum crimes. His death sentence became final after Supreme Court proceedings in 2006. He and six other condemned Aum members were executed in July 2018; further executions of Aum members followed later that month.
Those later proceedings did not erase the investigative errors experienced by Kono or the lasting harm to survivors and families. They did, however, establish criminal responsibility for the cult's organized campaign of violence.
Timeline
June 27, 1994: sarin is released in a residential district of Matsumoto. Residents die and hundreds are injured.
1995: after the Tokyo subway attack and the investigation of Aum Shinrikyo, evidence links the cult to Matsumoto.
2000–2006: a series of district, high-court and Supreme Court proceedings establish criminal responsibility for senior Aum members.
2018: Asahara and other condemned Aum members are executed after their convictions have become final.
Current status
The Matsumoto attack is solved and extensively adjudicated. Multiple Aum Shinrikyo members were convicted for their roles in the attack and related crimes. Current retrospectives record eight people killed and about 600 injured in Matsumoto.
The case also remains significant as a warning about wrongful early suspicion: Yoshiyuki Kono was never responsible for the attack, despite the attention directed at him before Aum's role became known.