The Teikoku Bank incident (Japanese: 帝銀事件, Teigin jiken[\*]) was a poisoning murder that took place on January 26, 1948, at the Shinamachi branch of the Teikoku Bank in Toshima, Tokyo, Japan. The incident also occurred in the chaotic postwar period, under the US military government of Japan, and its
Start Jan 26, 1948Last edited Oct 15, 2026, 2:51 PM
The Teikoku Bank incident also occurred in the chaotic postwar period under the US military government in Japan, and its mystery has still not been solved.
Overview of the incident
Occurrence of the incident
At about 3 p.m. on January 26, 1948, immediately after the bank had closed, a middle-aged man wearing an Armband indicating that he was from the Tokyo Metropolitan disinfection squad, and presenting an identification card of a Ministry of Health official, deceived 16 bank employees and family members of the janitor (aged 8 to 49) with statements such as "There has been a collective outbreak of Dysentery at a nearby house. Before GHQ disinfects the inside of the bank, please drink the preventive medicine," and "One of the infected people is on his way to the bank." He had them take Potassium cyanide. As a result, 11 people died on the spot, and one more died after being taken to a hospital. Taking advantage of this, the perpetrator stole 160,000 yen in cash and checks worth 17,450 yen, including checks from the Yasuda BankItabashi branch, and fled. However, because the scene was in chaos from the mass poisoning, the police's initial investigation was delayed, and they were ultimately unable to secure the perpetrator. Moreover, the checks the perpetrator had stolen began to be exchanged for cash from January 27, the day after the incident, but the people concerned did not confirm the theft of the checks until the morning of January 28, two days after the incident.
According to the survivors, the perpetrator used a drug whose effects appeared slowly so that all of the victims could drink enough of it. He also used a meticulous method, giving specific instructions on how to take it, such as having first taken it himself as a demonstration to avoid suspicion and saying, "Drink it with your tongue extended so that the enamel of your teeth is not damaged." Once the perpetrator had taken the drug himself, the bank employees came to trust him. When all 16 people had taken the first dose, they reportedly felt a burning sensation in their chests, like after drinking whiskey. Then, one minute later, when the perpetrator handed the victims a second dose, the victims, feeling a bitter taste, hurriedly drank it. When one bank employee asked to "rinse my mouth," the perpetrator allowed it. Just as all the victims were about to rinse their mouths at the kitchen sink, one female victim repeatedly fainted, and the perpetrator's scheme was exposed.
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On October 14, 1947, immediately after the bank had closed, a man who showed a business card reading "Technical official, medical doctor, Ministry of Health, Preventive Affairs Bureau, Shigeru Matsui"2 came and said, "It has been confirmed that a patient infected with dysentery came to deposit money this morning, so the staff in the bank and the money must be disinfected."3 The cautious branch manager made the man wait, called a police officer, and asked him about dysentery. The officer said, "This is out of the blue. Still, I will check with the station,"4 and went out. Until the officer returned, the man had the staff take medicine in the same way as at the Teikoku Bank. Fortunately, no one died. The business card itself was genuine, but Dr. Matsui had an Alibi, so he was not the culprit.
On January 19, 1948, immediately after the bank had closed, a man who showed an identification card reading "Technical official, medical doctor, Ministry of Health, Dr. Jiro Yamaguchi, Tokyo Metropolitan Preventive Affairs Section"6 came and said almost the same things as the man who had appeared at the Ebara branch of the Yasuda Bank. He had the bank staff take medicine and said the bank's money should be disinfected. When the suspicious branch manager replied that there had been no cash transport, the man sprayed a clear liquid called disinfectant on the small-amount bills the staff were sorting, and left. This business card was later found to be a fake.
Initial investigation
After the incident, the business card that the branch manager had received from the perpetrator was missing (the branch manager was absent at the time). The investigation proceeded using the branch manager's memory, the evidence from the two similar cases mentioned above, a composite sketch made from the testimonies of all the survivors, and the Checks that had been exchanged for cash the day after the incident as clues. The Tokyo Metropolitan Police Department narrowed down the profile of the perpetrator as follows.
Sanitation and disinfection division, public health division, health centers, hospitals, doctors, and pharmacists of ward and city offices.
Dentists, veterinarians, insurance physicians of life insurance companies, researchers and professors in medicine, chemistry, and pharmacy, students of those departments, drug manufacturers and distributors, drug brokers, and those with experience in these fields.
Interpreters, clerks, and general laborers of the occupying forces, or those with such experience.
Bank employees, or those with such experience.
Those with experience in disinfection work in flood-stricken areas.
Discharged soldiers or returned officers with medical knowledge.
Those who obtained or attempted to obtain cyanide from hospitals, clinics, pharmacies, etc., or who handle it professionally, or who enter factories or workshops that handle it.
Common points among the three cases
Location of the crimes: all were small banks outside the city center.8
Time of the crimes: Tuesday or Monday, after the bank had closed.8
Disguise: the perpetrator exposed his face, and wore on his left arm an armband printed with the words "disinfection squad" and the Tokyo mark. The intention was to inspire trust.9
Business cards: the perpetrator used business cards bearing titles of Ministry of Health institutions to make the victims believe him.9
Claimed to have returned from disinfecting a flood-stricken area.
Claimed that dysentery had broken out near the bank.
Claimed to have reported to the occupying forces and that a disinfection team had been dispatched under the orders of a certain Lieutenant (Parker, Marker, Hornet, Cotley, etc.).
Claimed that one of the patients had brought money to this bank.
Claimed that all items in the bank must be disinfected.
Demanded that all items be left as they were.
Asked whether there had been a cash transport.
Demanded that they take "preventive medicine" (actually poison) before the disinfection team arrived.
Demanded that they take a second dose one minute after taking the first.
Demanded that they drink with their tongues curled, claiming the medicine would damage tooth enamel.
Had everyone prepared cups, distributed the liquid with a dropper, and demonstrated by taking one himself.
When cyanide compounds were detected in the bodies, the investigation shifted mainly to former members of the Army's bacteriological unit (the so-called Unit 731), who knew how to handle such substances. A key lead was obtained from Ban Shigeo, who had belonged to the 9th Army Laboratory (commonly known as the Noborito Laboratory). On June 25, six months after the incident, the chief of the detective division instructed that the investigation be narrowed to some military personnel and to those who had been in Army special missions. The grounds for this were as follows.
The amount of potassium cyanide used by the perpetrator was only 0.2 to 0.5 grams, which almost matched the Lethal dose. The perpetrator achieved the maximum effect with the minimum amount of poison. If the perpetrator had been a novice, he would have increased the concentration or amount of the poison.1011
He left a one-minute interval between the first and second doses, and after one minute he abandoned the victims. This indicates he was confident that the poison would begin to act after one minute, leaving the victims no time to call for help from outside.11
The dropper used by the perpetrator was a Komagome-type Pipette, which was used in bacteriological research laboratories and laboratories belonging to the military. The shape and size of the pipette box were also similar to the surgical instrument boxes that military doctors carried in the field during World War II.12
Although the perpetrator attempted to poison 16 people at once, he was abnormally calm. He did not let a finger tremble when measuring or pouring the drug. This composure can be judged to have come from confidence born of experience.12
Furthermore, the poison used in the crime was not simple potassium cyanide. When potassium cyanide is taken, death occurs within a few seconds. However, the victims of this incident began to be affected by the poison one minute later. The investigation found that it resembled Acetone cyanohydrin (commonly called nitrile), which had been developed at the Noborito Laboratory. The Metropolitan Police believed the perpetrator was among the demobilized members of Shiro Ishii's group, which had studied various biological warfare agents in Manchuria, and of Unit 731 which he led. The gist of the investigation guidelines at that time was as follows.13
Those with experience in medicine, disinfection, drug handling, or research and experimentation, and especially discharged soldiers, researchers in military-related fields, special service agency personnel, and military police, are considered the most suitable candidates.
Exercise caution in searching for the relevant persons.
Since most of the persons concerned are likely to be employed in medicine, disinfection, or pharmaceuticals, special care is needed in the investigation.
When there is no suspicion, investigate by asking about other relevant persons in the same unit.
Meanwhile, the calling-card team, which had been a supporting presence within the investigation headquarters, pursued the investigation and focused on the business card of Shigeru Matsui, which had been misused in the similar cases. (This card team included the legendary detective Hachibe Hiratsuka.) Since the dates, places, and persons to whom Matsui's cards had been handed out were recorded, the investigation proceeded accordingly. Of the 100 cards, 8 remained with Dr. Matsui, and of the remaining 92, the team succeeded in recovering 62 and confirmed that 22 had been lost and could be considered unrelated to the incident. Of the 8 whose whereabouts could never be determined, one was believed to have been used in the incident.
The reasons for Hirasawa's arrest were as follows.
Among those who had received "Shigeru Matsui's Business card," Hirasawa did not possess one. (Hirasawa had reported to the police that his wallet had been stolen.)
Hirasawa stated that he "was walking near the scene at the time of the incident,"14 but he could not prove his Alibi.
Immediately after the incident, he deposited money in an amount nearly equal to the total amount of the damages, and the source of that money was not clearly known.15
The police confronted Hirasawa with the victims, but not one of them asserted that Hirasawa was a different person from the perpetrator. From the time of his arrest, Hirasawa consistently denied the crimes, but beginning on September 23 he started to confess, and on October 12 he was indicted for robbery-murder and attempted robbery-murder, in connection with the Teikoku Bank incident and two other attempted cases. In the trial held at the Tokyo District Court from December 20, Hirasawa retracted his confession and claimed innocence. However, on July 24, 1950, the Tokyo District Court handed down a death sentence at first instance; on September 29, 1951, the Tokyo High Court dismissed the appeal; and on April 7, 1955, the Supreme Court of Japan dismissed the final appeal, and on May 7 the death sentence was finalized.
Death sentence and campaign for retrial
Seicho Matsumoto, Komiyama Yushiro (小宮山重四郎), and other supporters began a campaign to save Hirasawa's life. Hirasawa's supporters argued that his statements were unreliable, as they were the product of interrogation close to torture and of a psychiatric condition (confabulation) resulting from the aftereffects of Korsakoff syndrome, caused by side effects of RabiesVaccination. Moreover, according to the appraisal of Dr. Ōmura Tokuzō (大村徳三), three confession records, which had been decisive in the death sentence, were produced by having Hirasawa's fingerprints pressed onto blank paper by Prosecutor Ide Yoshio (出射義夫), who had not been involved in the interrogation. Seventeen retrial petitions and three requests for special pardon were filed, but all were rejected.
Six years after the incident, in 1954, a mass murder occurred in Ibaraki Prefecture in which people were given cyanide by someone posing as a Public health center employee. Because this method was extremely similar to that of the Teikoku Bank incident, Hirasawa's defense attorneys infiltrated the area to investigate, but since the arrested suspect had committed suicide by poisoning, they gained nothing.
In 1962, Hirasawa was transferred to Miyagi Prison, and the magazine Time questioned whether this was an attempt to let him die a natural death by sending him to the poor environment of the Tōhoku region.16 In 1968, the Retrial Special Provisions Bill was submitted, and in 1969, when the bill was scrapped, the Minister of Justice considered individual special pardons for seven death-row inmates; Hirasawa was also among those considered, but in the end no special pardon was granted to him.
As successive Ministers of Justice all refused to sign Hirasawa's execution order, on May 10, 1987, Hirasawa died of pneumonia in the Hachioji Medical Prison. He was 95 years old. On May 25, immediately after Hirasawa's death, Ban Shigeo, who had cooperated with the investigation headquarters, appeared on television and emphasized that the culprit was not Hirasawa but a former member of the Imperial Japanese Army. Hideo Naruchi (成智英雄), who had participated in the investigation, later wrote in his memoir that "The Teikoku Bank incident was impossible for a person like Hirasawa, who had no knowledge whatsoever of poisons; the real culprit was a person who had originally been in a secret unit,"17 and went further to claim that "Of the more than 50 members of Unit 731 investigated, only Lieutenant Colonel S (51 years old at the time of the incident, died of illness the year after the incident) matched in background, alibi, and appearance."18 However, no one in Unit 731 matched "Lieutenant Colonel S" in both surname and given name. There was testimony that two other men with similar surnames and similar given names existed, so Naruchi may have confused two or more people.
Even after Hirasawa's death, his adopted son and supporters have continued to file retrial petitions to restore his reputation. As of 2008 (Heisei 20), a 19th retrial petition is pending at the Tokyo High Court.
Questions about the poison
Autopsies of the bodies and analysis of the liquid remaining in the vomit and vessels were carried out at the University of Tokyo and Keio University. However, because the liquid had been poorly stored, only the fact that it was a cyanide compound was determined, and the appraisals of Tanemoto Furuhata of the University of Tokyo and Kyuhei Nakadate of Keio University conflicted, so no appraisal with 100% accuracy was reached.
At that time, a reporter of the Yomiuri Shimbun discovered that the 9th Army Laboratory had developed a drug called acetone cyanohydrin (cyanide nitrile). Compared with ordinary potassium cyanide, which takes effect immediately, cyanide nitrile has a delayed effect, appearing one or two minutes after ingestion. However, while the autopsy results had only established that the substance was a cyanide compound, and as the police investigation moved far away from Unit 731, reporting and coverage were also inevitably forced to change direction, and coverage of Unit 731 was halted.
Later, when the US military government's documents were declassified, in 1985 (Showa 60) the Yomiuri Shimbun reported the following facts.
The perpetrator's method matched the poison-handling guidelines prepared by the military's secret scientific research institute.
The equipment used in the crime matched that used at the same institute.
In March 1948 (Showa 23), the US military government banned investigation and reporting related to Unit 731.
Other
The news media published photographs of the scene with bodies lined up.19 However, complaints were raised about the photographs showing the lined-up bodies, and it is said that Japanese news organizations thereafter became reluctant to use photographs of corpses.20
There is a theory that this deposit came from money earned by selling Shunga (erotic prints) that he had painted, but he denied this, and the source remains unclear. Seicho Matsumoto, in the novel The Teikoku Bank Incident (小説帝銀事件), speculated that he denied it because if it became known that he had painted shunga, it would harm Hirasawa's reputation as a painter. ↩
The Teikoku Bank incident also occurred in the chaotic postwar period under the US military government in Japan, and its mystery has still not been solved.
Overview of the incident
Occurrence of the incident
At about 3 p.m. on January 26, 1948, immediately after the bank had closed, a middle-aged man wearing an Armband indicating that he was from the Tokyo Metropolitan disinfection squad, and presenting an identification card of a Ministry of Health official, deceived 16 bank employees and family members of the janitor (aged 8 to 49) with statements such as "There has been a collective outbreak of Dysentery at a nearby house. Before GHQ disinfects the inside of the bank, please drink the preventive medicine," and "One of the infected people is on his way to the bank." He had them take Potassium cyanide. As a result, 11 people died on the spot, and one more died after being taken to a hospital. Taking advantage of this, the perpetrator stole 160,000 yen in cash and checks worth 17,450 yen, including checks from the Yasuda BankItabashi branch, and fled. However, because the scene was in chaos from the mass poisoning, the police's initial investigation was delayed, and they were ultimately unable to secure the perpetrator. Moreover, the checks the perpetrator had stolen began to be exchanged for cash from January 27, the day after the incident, but the people concerned did not confirm the theft of the checks until the morning of January 28, two days after the incident.
According to the survivors, the perpetrator used a drug whose effects appeared slowly so that all of the victims could drink enough of it. He also used a meticulous method, giving specific instructions on how to take it, such as having first taken it himself as a demonstration to avoid suspicion and saying, "Drink it with your tongue extended so that the enamel of your teeth is not damaged." Once the perpetrator had taken the drug himself, the bank employees came to trust him. When all 16 people had taken the first dose, they reportedly felt a burning sensation in their chests, like after drinking whiskey. Then, one minute later, when the perpetrator handed the victims a second dose, the victims, feeling a bitter taste, hurriedly drank it. When one bank employee asked to "rinse my mouth," the perpetrator allowed it. Just as all the victims were about to rinse their mouths at the kitchen sink, one female victim repeatedly fainted, and the perpetrator's scheme was exposed.
Before this incident, there had been two attempted cases with similar methods, as follows.
On October 14, 1947, immediately after the bank had closed, a man who showed a business card reading "Technical official, medical doctor, Ministry of Health, Preventive Affairs Bureau, Shigeru Matsui"2 came and said, "It has been confirmed that a patient infected with dysentery came to deposit money this morning, so the staff in the bank and the money must be disinfected."3 The cautious branch manager made the man wait, called a police officer, and asked him about dysentery. The officer said, "This is out of the blue. Still, I will check with the station,"4 and went out. Until the officer returned, the man had the staff take medicine in the same way as at the Teikoku Bank. Fortunately, no one died. The business card itself was genuine, but Dr. Matsui had an Alibi, so he was not the culprit.
On January 19, 1948, immediately after the bank had closed, a man who showed an identification card reading "Technical official, medical doctor, Ministry of Health, Dr. Jiro Yamaguchi, Tokyo Metropolitan Preventive Affairs Section"6 came and said almost the same things as the man who had appeared at the Ebara branch of the Yasuda Bank. He had the bank staff take medicine and said the bank's money should be disinfected. When the suspicious branch manager replied that there had been no cash transport, the man sprayed a clear liquid called disinfectant on the small-amount bills the staff were sorting, and left. This business card was later found to be a fake.
Initial investigation
After the incident, the business card that the branch manager had received from the perpetrator was missing (the branch manager was absent at the time). The investigation proceeded using the branch manager's memory, the evidence from the two similar cases mentioned above, a composite sketch made from the testimonies of all the survivors, and the Checks that had been exchanged for cash the day after the incident as clues. The Tokyo Metropolitan Police Department narrowed down the profile of the perpetrator as follows.
Sanitation and disinfection division, public health division, health centers, hospitals, doctors, and pharmacists of ward and city offices.
Dentists, veterinarians, insurance physicians of life insurance companies, researchers and professors in medicine, chemistry, and pharmacy, students of those departments, drug manufacturers and distributors, drug brokers, and those with experience in these fields.
Interpreters, clerks, and general laborers of the occupying forces, or those with such experience.
Bank employees, or those with such experience.
Those with experience in disinfection work in flood-stricken areas.
Discharged soldiers or returned officers with medical knowledge.
Those who obtained or attempted to obtain cyanide from hospitals, clinics, pharmacies, etc., or who handle it professionally, or who enter factories or workshops that handle it.
Common points among the three cases
Location of the crimes: all were small banks outside the city center.8
Time of the crimes: Tuesday or Monday, after the bank had closed.8
Disguise: the perpetrator exposed his face, and wore on his left arm an armband printed with the words "disinfection squad" and the Tokyo mark. The intention was to inspire trust.9
Business cards: the perpetrator used business cards bearing titles of Ministry of Health institutions to make the victims believe him.9
Claimed to have returned from disinfecting a flood-stricken area.
Claimed that dysentery had broken out near the bank.
Claimed to have reported to the occupying forces and that a disinfection team had been dispatched under the orders of a certain Lieutenant (Parker, Marker, Hornet, Cotley, etc.).
Claimed that one of the patients had brought money to this bank.
Claimed that all items in the bank must be disinfected.
Demanded that all items be left as they were.
Asked whether there had been a cash transport.
Demanded that they take "preventive medicine" (actually poison) before the disinfection team arrived.
Demanded that they take a second dose one minute after taking the first.
Demanded that they drink with their tongues curled, claiming the medicine would damage tooth enamel.
Had everyone prepared cups, distributed the liquid with a dropper, and demonstrated by taking one himself.
When cyanide compounds were detected in the bodies, the investigation shifted mainly to former members of the Army's bacteriological unit (the so-called Unit 731), who knew how to handle such substances. A key lead was obtained from Ban Shigeo, who had belonged to the 9th Army Laboratory (commonly known as the Noborito Laboratory). On June 25, six months after the incident, the chief of the detective division instructed that the investigation be narrowed to some military personnel and to those who had been in Army special missions. The grounds for this were as follows.
The amount of potassium cyanide used by the perpetrator was only 0.2 to 0.5 grams, which almost matched the Lethal dose. The perpetrator achieved the maximum effect with the minimum amount of poison. If the perpetrator had been a novice, he would have increased the concentration or amount of the poison.1011
He left a one-minute interval between the first and second doses, and after one minute he abandoned the victims. This indicates he was confident that the poison would begin to act after one minute, leaving the victims no time to call for help from outside.11
The dropper used by the perpetrator was a Komagome-type Pipette, which was used in bacteriological research laboratories and laboratories belonging to the military. The shape and size of the pipette box were also similar to the surgical instrument boxes that military doctors carried in the field during World War II.12
Although the perpetrator attempted to poison 16 people at once, he was abnormally calm. He did not let a finger tremble when measuring or pouring the drug. This composure can be judged to have come from confidence born of experience.12
Furthermore, the poison used in the crime was not simple potassium cyanide. When potassium cyanide is taken, death occurs within a few seconds. However, the victims of this incident began to be affected by the poison one minute later. The investigation found that it resembled Acetone cyanohydrin (commonly called nitrile), which had been developed at the Noborito Laboratory. The Metropolitan Police believed the perpetrator was among the demobilized members of Shiro Ishii's group, which had studied various biological warfare agents in Manchuria, and of Unit 731 which he led. The gist of the investigation guidelines at that time was as follows.13
Those with experience in medicine, disinfection, drug handling, or research and experimentation, and especially discharged soldiers, researchers in military-related fields, special service agency personnel, and military police, are considered the most suitable candidates.
Exercise caution in searching for the relevant persons.
Since most of the persons concerned are likely to be employed in medicine, disinfection, or pharmaceuticals, special care is needed in the investigation.
When there is no suspicion, investigate by asking about other relevant persons in the same unit.
Meanwhile, the calling-card team, which had been a supporting presence within the investigation headquarters, pursued the investigation and focused on the business card of Shigeru Matsui, which had been misused in the similar cases. (This card team included the legendary detective Hachibe Hiratsuka.) Since the dates, places, and persons to whom Matsui's cards had been handed out were recorded, the investigation proceeded accordingly. Of the 100 cards, 8 remained with Dr. Matsui, and of the remaining 92, the team succeeded in recovering 62 and confirmed that 22 had been lost and could be considered unrelated to the incident. Of the 8 whose whereabouts could never be determined, one was believed to have been used in the incident.
The reasons for Hirasawa's arrest were as follows.
Among those who had received "Shigeru Matsui's Business card," Hirasawa did not possess one. (Hirasawa had reported to the police that his wallet had been stolen.)
Hirasawa stated that he "was walking near the scene at the time of the incident,"14 but he could not prove his Alibi.
Immediately after the incident, he deposited money in an amount nearly equal to the total amount of the damages, and the source of that money was not clearly known.15
The police confronted Hirasawa with the victims, but not one of them asserted that Hirasawa was a different person from the perpetrator. From the time of his arrest, Hirasawa consistently denied the crimes, but beginning on September 23 he started to confess, and on October 12 he was indicted for robbery-murder and attempted robbery-murder, in connection with the Teikoku Bank incident and two other attempted cases. In the trial held at the Tokyo District Court from December 20, Hirasawa retracted his confession and claimed innocence. However, on July 24, 1950, the Tokyo District Court handed down a death sentence at first instance; on September 29, 1951, the Tokyo High Court dismissed the appeal; and on April 7, 1955, the Supreme Court of Japan dismissed the final appeal, and on May 7 the death sentence was finalized.
Death sentence and campaign for retrial
Seicho Matsumoto, Komiyama Yushiro (小宮山重四郎), and other supporters began a campaign to save Hirasawa's life. Hirasawa's supporters argued that his statements were unreliable, as they were the product of interrogation close to torture and of a psychiatric condition (confabulation) resulting from the aftereffects of Korsakoff syndrome, caused by side effects of RabiesVaccination. Moreover, according to the appraisal of Dr. Ōmura Tokuzō (大村徳三), three confession records, which had been decisive in the death sentence, were produced by having Hirasawa's fingerprints pressed onto blank paper by Prosecutor Ide Yoshio (出射義夫), who had not been involved in the interrogation. Seventeen retrial petitions and three requests for special pardon were filed, but all were rejected.
Six years after the incident, in 1954, a mass murder occurred in Ibaraki Prefecture in which people were given cyanide by someone posing as a Public health center employee. Because this method was extremely similar to that of the Teikoku Bank incident, Hirasawa's defense attorneys infiltrated the area to investigate, but since the arrested suspect had committed suicide by poisoning, they gained nothing.
In 1962, Hirasawa was transferred to Miyagi Prison, and the magazine Time questioned whether this was an attempt to let him die a natural death by sending him to the poor environment of the Tōhoku region.16 In 1968, the Retrial Special Provisions Bill was submitted, and in 1969, when the bill was scrapped, the Minister of Justice considered individual special pardons for seven death-row inmates; Hirasawa was also among those considered, but in the end no special pardon was granted to him.
As successive Ministers of Justice all refused to sign Hirasawa's execution order, on May 10, 1987, Hirasawa died of pneumonia in the Hachioji Medical Prison. He was 95 years old. On May 25, immediately after Hirasawa's death, Ban Shigeo, who had cooperated with the investigation headquarters, appeared on television and emphasized that the culprit was not Hirasawa but a former member of the Imperial Japanese Army. Hideo Naruchi (成智英雄), who had participated in the investigation, later wrote in his memoir that "The Teikoku Bank incident was impossible for a person like Hirasawa, who had no knowledge whatsoever of poisons; the real culprit was a person who had originally been in a secret unit,"17 and went further to claim that "Of the more than 50 members of Unit 731 investigated, only Lieutenant Colonel S (51 years old at the time of the incident, died of illness the year after the incident) matched in background, alibi, and appearance."18 However, no one in Unit 731 matched "Lieutenant Colonel S" in both surname and given name. There was testimony that two other men with similar surnames and similar given names existed, so Naruchi may have confused two or more people.
Even after Hirasawa's death, his adopted son and supporters have continued to file retrial petitions to restore his reputation. As of 2008 (Heisei 20), a 19th retrial petition is pending at the Tokyo High Court.
Questions about the poison
Autopsies of the bodies and analysis of the liquid remaining in the vomit and vessels were carried out at the University of Tokyo and Keio University. However, because the liquid had been poorly stored, only the fact that it was a cyanide compound was determined, and the appraisals of Tanemoto Furuhata of the University of Tokyo and Kyuhei Nakadate of Keio University conflicted, so no appraisal with 100% accuracy was reached.
At that time, a reporter of the Yomiuri Shimbun discovered that the 9th Army Laboratory had developed a drug called acetone cyanohydrin (cyanide nitrile). Compared with ordinary potassium cyanide, which takes effect immediately, cyanide nitrile has a delayed effect, appearing one or two minutes after ingestion. However, while the autopsy results had only established that the substance was a cyanide compound, and as the police investigation moved far away from Unit 731, reporting and coverage were also inevitably forced to change direction, and coverage of Unit 731 was halted.
Later, when the US military government's documents were declassified, in 1985 (Showa 60) the Yomiuri Shimbun reported the following facts.
The perpetrator's method matched the poison-handling guidelines prepared by the military's secret scientific research institute.
The equipment used in the crime matched that used at the same institute.
In March 1948 (Showa 23), the US military government banned investigation and reporting related to Unit 731.
Other
The news media published photographs of the scene with bodies lined up.19 However, complaints were raised about the photographs showing the lined-up bodies, and it is said that Japanese news organizations thereafter became reluctant to use photographs of corpses.20
There is a theory that this deposit came from money earned by selling Shunga (erotic prints) that he had painted, but he denied this, and the source remains unclear. Seicho Matsumoto, in the novel The Teikoku Bank Incident (小説帝銀事件), speculated that he denied it because if it became known that he had painted shunga, it would harm Hirasawa's reputation as a painter. ↩