The Matsumoto incident was an act of domestic terrorism perpetrated by members of Aum Shinrikyo in Matsumoto, Japan, in Nagano prefecture, on the evening of June 27 and the morning of June 28, 1994. Eight people were killed and over 200 were harmed by sarin gas that was released from several sites in the Kaichi Heights area. This incident was perpetrated about nine months before the better known Tokyo subway sarin attack.
The first calls to emergency officials occurred around 11:00 p.m.; by 4:15 a.m. the following morning, six people had died from the poison. On July 3, officials announced that the toxic agent had been identified as sarin using gas chromatography–mass spectrometry. The dead included Yutaka Kobayashi, a 23-year old salaried worker, and Yasumoto, a 29-year old medical school student. The sarin used in the incident was nearly pure.
Although an anonymous tip implicating Aum Shinrikyo was given to police after the gassing, the sect was not officially implicated in this incident until after the later Tokyo attack. One section read, "Matsumoto was definitely an experiment of sorts. The result of this experiment in an open space: seven dead, over 200 injured. If sarin is released in an enclosed space say, a crowded subway it is easy to imagine a massive catastrophe."
After the incident, police focused their investigation on Yoshiyuki Kōno, whose wife was a victim put in a coma by the gas. It was discovered that Kōno had stored a large amount of pesticide in his residence. Despite the fact that sarin cannot be manufactured from pesticides, Keiichi Tsuneishi, a Japanese historian, claimed the nerve agent is synthesizable from organophosphorus pesticides, and Kōno was dubbed by some in the media "the Poison Gas Man" and received hate mail, death threats, and intense legal pressure. After he was found innocent, every major Japanese newspaper apologized to Kōno, including those who did not name him as a suspect.
After the attack on the Tokyo subway in 1995, the blame was shifted to the cult Aum Shinrikyo. The police chief, on behalf of the police department and media, publicly apologized to Kōno. Kōno's wife later woke up from coma, but recovered neither speech nor body movement and eventually died in 2008.
Several Aum Shinrikyo members were found guilty of masterminding both incidents. Combined, the attacks resulted in 21 deaths and thousands of hospitalizations or outpatient treatment. The main motive for the Matsumoto incident was trying to kill the judges handling fraud charges against Aum brought by land owners in Matsumoto, in order to prevent the court from releasing the scheduled verdict. Aum had also used Matsumoto as a test for their future plans to release the gas in Tokyo.
- "Main Matsumoto sarin victim dies 14 years after attack" The Yomiuri Shimbun (August 6, 2008).
- "Survivor of Aum's '94 sarin attack dies while in coma" The Asahi Shimbun (August 6, 2008).
- Kyodo News, "Matsumoto gassings remembered", Japan Times, June 28, 2009, p. 2.
- Clinical review: Tokyo – protecting the health care worker during a chemical mass casualty event: an important issue of continuing relevance
- Guinea Pigs FALSE PROPHET: THE AUM CULT OF TERROR (chapter 18), Patrick Bellamy
- Keiichi, Tsuneishi (June 28, 1994). "ナゾの有毒ガスで７人死亡 農薬中毒に似る 松本市の住宅街" [Mysterious toxic gas killed seven people, resembles pesticide intoxication, residental area of Matsumoto city]. The Asahi Shimbun, evening edition.
- Keiichi, Tsuneishi (July 4, 1994). "市販薬でも作れる猛毒サリン 知識や経験あれば可能 松本の中毒死" [Deadly poisonous sarin synthesizable from over-the-counter drug, possible with experience and knowledge. Death by poisoning in Matsumoto]. The Asahi Shimbun, morning edition.
- Danzig, Richard, Marc Sageman, Terrance Leighton, Lloyd Hough, Hidemi Yuki, Rui Kotani and Zachary M. Hosford, "Aum Shinrikyo: Insights Into How Terrorists Develop Biological and Chemical Weapons" (Archive), Center for a New American Security, July 2011.