Investigations after the Matsumoto attack were generally inconclusive, with the primary suspect being Yoshiyuki Kōno, whose wife had been left comatose by the attack. Blame would not be clearly attributed to Aum Shinrikyo until after the subway attack, despite tipoffs – in September 1994, two anonymous letters were sent to major media outlets in Japan – the first asserting that the group were responsible for the attack, and the second claiming that Matsumoto was an open-air 'experiment of sorts', noting that the results would have been much worse if sarin had been released indoors, such as in 'a crowded subway'.
