Sadamichi Hirasawa

[2][3] On January 26, 1948, a man calling himself an epidemiologist arrived at a branch of the Imperial Bank (Teikoku Ginkō, aka Teigin) in Shiinamachi, a suburb of Toshima, Tokyo, shortly before closing time.

He explained that he was a public health official sent by US occupation authorities who had orders to inoculate the staff against a sudden outbreak of dysentery.

Those present drank the liquid he gave, which was later thought to be "nitrile hydrocyanide" (青酸ニトリール), an assassination toxicant originally developed at the Noborito Laboratory.

When all were incapacitated, the robber took some money lying on the desks, which amounted to 160,000 yen (about $2,000 US at the time), but left the majority behind, leaving his motive unknown.

The poisoner also used a real card which was marked "Shigeru Matsui" (of the Ministry of Health and Welfare, Department of Disease Prevention) in another of the two incidents.

[4] Seichō Matsumoto presumed that the true culprit was a former member of Unit 731 in his books A story of the Teikoku Bank Incident in 1959 and The Black Fog of Japan in 1960.

However, the Japanese court refused this argument, pointing out that the statute only applies in the case if a death row inmate escapes from prison and evades capture for 30 years.

According to supporters, the pressures and uncertainties surrounding the reopening of the case, together with his mother's death, had caused Takehiko to periodically display signs of instability and doubts about whether he could continue.

He continued to persist with his objective of getting a posthumous retrial, though - writing after his mother's death on a website about the "Teigin Incident": It was her wish and mine and my late father’s to mark in history that Sadamichi Hirasawa is innocent.

[14]At the time of Takehiko's death, he and his lawyers had assembled a team of psychologists to reexamine the witness accounts and investigation process from the trial, to determine if the evidence was credible by present standards.

[14] On 4 December 2013, the Tokyo High Court announced it would drop the plea for a posthumous retrial for Sadamichi Hirasawa following his adopted son's death.

[15] The Teigin incident is the basis for The Aosawa Murders, a 2005 Japanese crime novel written by Riku Onda, which describes a fictional mass poisoning case in Japan in 1973.

A 2009 novel, Occupied City by English author David Peace, who was long a resident in Japan, is based on the Hirasawa case.