Yoshiyuki Kouno (河野 義行, born 1950) was a victim of the Matsumoto incident, a sarin attack that killed seven people and sickened many more in Matsumoto, Japan, on the evening of June 27 and the morning of June 28, 1994.
After the incident, the investigating police considered Yoshiyuki Kouno a suspect in the crime. Japanese media dubbed Kouno the "Poison Gas Man" and he subsequently received hate mail and death threats. However, after the much larger attack on the Tokyo subway in 1995, Kouno was cleared of blame, Aum Shinrikyo was deemed responsible. The head of National Public Safety Commission Hiromu Nonaka and media publicly apologized to Kouno. However, Nagano police had never directly apologized to Kouno until 2002.
While no sufficient evidence of Kouno's involvement was found, he was accused by the media in perpetrating the attack when police hinted at possibility of his involvement. While actually this was in violation of basic legal rights of the citizen, police could get away with it since the source that provided the information to the media was quoted as anonymous.
Kouno later participated in many media events in defence of Aum, arguing that since the time he was wrongly accused in connection to the incident, he realized how vulnerable innocent victims are to media hate campaigns. Pointing to his own personal experience with the media industry and police, he drew parallels to innocent Aum members who suffered public alienation and unceremonious intrusion into their private life justified mostly by fears generated by the sensationalistic media rather than any proof of actual guilt. Together with Yoshihiro Yasuda, a veteran attorney arrested during his defence of Aum's founder Shoko Asahara, he also campaigned against the death penalty and delivered speeches and lectures explaining the impact of Japan's judicial system on suspects and wrongly accused, as well as the social impact on relatives and associates.