At the Education and Research Center of Legal Medicine (Chiba University), we perform autopsies and various tests on deceased individuals, mainly from Chiba Prefecture, when law enforcement agencies have identified the need for forensic investigation. Our objective is to determine the cause of death from a medical perspective. Additionally, we perform DNA analyses and dental examinations for the purpose of body identification. Furthermore, we receive requests from child consultation centers, prosecution teams, and the prefectural police regarding live individuals, for which we provide forensic diagnoses.

In 2022, the total number of autopsies conducted amounted to 390, marking an increase of 19 compared to the 371 autopsies performed at Chiba University in 2021. While the number of judicial autopsies increased, there was a decline in administrative autopsies, and autopsies performed in compliance with the Death Investigation and Identification Act (hereafter “the Investigation Act”) relative to 2021. The School of Medicine at the International University of Health and Welfare was newly established in 2018, and from 2021, Nippon Medical School began conducting autopsies in Chiba Prefecture. Both these developments contributed to the reduction of autopsies at Chiba University, but the increase in overall autopsy numbers was even greater.

The Basic Act for the Promotion of Death Investigation came into effect in April 2020, with the Promotion Plan subsequently being ratified by the Cabinet in June 2021. These measures were based on discussions that took place at the Promotion Council. However, most of the plans had been previously declared, and we were not able to see the expected new measures. In the future, we hope that effective reform policies will be developed, including the Child Death Review, which is also stipulated in the Basic Act for Child Growth. However, as the model project does not include cases of death for which judicial autopsies have been performed, it is challenging to anticipate due consideration being given to issues of abuse, accidents, and suicide.

Notably, we not only collect relevant information on dead people, determine the exact cause of death of each individual, and identify bodies, but we also clarify the death trends in Japan and help prevent accidents and disasters as well as the recurrence of murders and suicides. Our social mission is to maintain and improve the safety and health of the population. Given this context, we aim to increase awareness of present challenges by providing information on the causes of death, and we hope to contribute to system improvements by initiating constructive discussions leading to modifications in how causes of death are investigated in our country.

Classifying the manner and causes of death

In this report, the manner of death is classified as follows: natural, accidental, suicide, homicide, undetermined external cause, and undetermined. For the cause of death deemed as ‘natural’ we employ the medium rank classification from the simple classification of causes, drawing on vital statistics data obtained from the Ministry of Health, Labour and Welfare. Accidental deaths are further sub-divided based on the results indicated on the corpse examination certificate, such as traffic accidents, falls, drowning, asphyxiation, fire, and other causes. For cases of suicide, we use the classification of the Tokyo Metropolitan Medical Examiner’s Office and classify cases as hanging, sharp force, gunshot wound (GSW), drugs and poisoning, drowning, use of a moving vehicle, thermal injury, jumping from a high place, and other causes. For cases of homicide, we refer to the classification used by medical examiners in the United States and classify cases as child abuse, strangulation, sharp force, GSW, fire and thermal injury, blunt force, and other causes. While many countries use five classifications for specifying the manner of death, in Japan, due to a significant proportion of unidentified bodies with undetermined manners of death, we introduce the “undetermined external death” category. This is reserved for cases in which we do not know the manner of death but can determine its direct cause, such as drowning.



In 2022, the population of Chiba Prefecture was approximately 6,210,000. A total of 73,027 deaths were reported in this prefecture; overall, 10,999 deaths were reported to the police department, 10,805 to detectives, and 194 to the Traffic Bureau. A total of 487 judicial autopsies were performed―a 12.7% increase compared with the previous year. In all, 580 deaths were managed by the police department, nine by the Coast Guard, and three by Chiba District Prosecution. Among all autopsies performed during this year, 11 were administrative autopsies. In compliance with the Investigation Act, 94 autopsies were performed. The total number of medicolegal autopsies was 592, and the autopsy rate per death was approximately 0.8% (the rate in Japan was approximately 1.5%).

Overall, 390 medicolegal autopsies were performed at our center in 2022―a 5.1% increase compared to the previous year. These autopsies included 364 judicial autopsies, 10 administrative autopsies, and 16 autopsies performed in compliance with the Investigation Act. Among the judicial autopsies, 359 were commissioned by the Chiba Prefectural Police (343 by detectives and 16 by the Traffic Bureau), three by the Chiba District Prosecution, one by the Ibaraki Prefectural Police Department, and one by the Coast Guard. Of the 10 administrative autopsies, five were handled by detectives and five by the Traffic Bureau.

In the fiscal year 2018, forensic pathologists in the center, instead of physicians, began to perform some services under the jurisdiction of the Chiba Central Police Office. They performed 24 postmortem examinations in 2022. Apart from autopsies, forensic radiologists performed 24 postmortem examinations using computed tomography (CT).

Laboratory examinations, drug and poison tests, pathology organization inspection, blood typing, blood biochemical tests, and other tests were performed on all corpses as required, and specimens were obtained. Where required, the bodies were examined for signs of carbon monoxide poisoning and the presence of plankton and sperm. First, we performed CT imaging studies; subsequently, we performed autopsies, obtained various test results, investigated the situation of the deceased, and comprehensively estimated the cause and manner of death.

With respect to the services of forensic odontology and genetics, we confirmed the identity of unidentified human remains using dental records and deoxyribonucleic acid (DNA) testing. However, as a rule, DNA-type testing of corpses handled by the police had to be conducted at a crime laboratory. Thus, the Chiba Prefectural Police did not request this service. In addition to requests from the Coast Guard, we incorporated testing of cases other than those in Chiba, according to cooperative agreements with other universities.

Regarding clinical forensic medicine, we received 75 requests from child consultation centers in Chiba Prefecture, Chiba City, Chiba Prefectural Police, and the Chiba District Prosecution. Accordingly, we established the forensic diagnosis.


Judicial autopsies

In 2022, judicial autopsies were performed on 364 corpses. The details are outlined in the following tables.

Table 1 shows the nationalities of the corpses managed by our center in 2022. Thirteen were foreign nationals from five regions (Southeast Asia 6, East Asia 4, South Asia 1, North America 1, and South America 1). In addition, one case from East Asia was identified in autopsies performed in compliance with the Investigation Act.

Table 2 shows the manner of death for all corpses managed by our center. We recorded 73 (20%) natural deaths, 91 (25%) accidents, 71 (19%) suicides, 21 (6%) homicides, 33 (9%) deaths associated with undetermined external causes, and 75 (21%) deaths due to unknown causes. The fatality rate was approximately 2.1-fold higher in men than in women, and men outnumbered women in other manners of death other than homicides.

Table 3 shows the age distribution of the corpses managed at our center. The mean and median ages were 62 and 67 years, respectively, showing little difference from the previous years. The mean age based on the cause of death was 54 years for suicide, 56 years for homicide, 68 years for natural death, and 65 years for accidental death.

Table 4 shows the monthly distribution of deaths based on the type and number of deaths. Although the number was slightly higher in December, no significant difference was observed.

Tables 5 and 6 show the causes of natural deaths. Although the number of deaths was too low to describe the results accurately, the causes of natural deaths were similar to those that contributed to the overall mortality statistics of the population (heart disease, malignant neoplasm, and cerebrovascular disease). In addition, many behavioral disorders are caused by malnutrition and dehydration. We observed that two-thirds of the deaths attributable to natural causes occurred in patients aged >64 years old.

Tables 7 and 8 list the causes of accidental deaths. In 2022, fires were observed to be the leading cause of death, as in previous years, followed by drowning, other accidental deaths and falls. The frequency of traffic accidents persisted at levels comparable to those of 2021. Many other accidental deaths were attributed to heat stroke, hypothermia, and work-related deaths, which did not meet the criteria for a specific category. By age group, the average age in fire incidents was 76, and the damage caused by elderly people's delay in evacuation was conspicuous. Furthermore, 2022 witnessed a relatively higher number of falls, with the mean age for this category being 78 years old.

Tables 9 and 10 list the methods of suicide. The most common means of suicide was hanging, followed by drugs and poisoning. Notably, out of the 17 cases related to poisoning, nine were attributed to carbon monoxide poisoning using briquettes. Thereafter, drowning and jumping from high places were the most frequent methods. In terms of sex distribution, national statistics showed an increase in the percentage of female suicides. However, in Chiba, men were still the majority. Age-wise, the predominant bracket comprised individuals aged between 45 and 64 years.

Tables 11 and 12 list the homicidal deaths recorded in 2022 and the methods used. The number of homicide cases was almost the same as in previous years. Regarding means of homicides, stabbing and blunt force were the top two. The gender distribution was approximately balanced, with men and women being almost equally represented. Throughout 2022, homicide victims spanned a broad age spectrum.

Among the 33 deaths due to undetermined external causes, 15 were attributed to drowning and four to fire. Regarding the other cases, although we could determine the direct cause of death, the manner of death (accident, suicide, or homicide) remained undetermined.

Among the 75 deaths due to unknown causes, it was difficult to identify the cause of death in 65 cases due to bleached bones, corpse wax, mummification, or significantly decomposed corpses, including one case suspected to be suicide. Among the remaining cases, one involved the sudden death of an infant.


Administrative autopsies

Among the 10 bodies autopsied for administrative purposes, there was an equal distribution of men and women. Their ages ranged from 3 to 90 years, with mean and median ages of 65 and 76 years, respectively. We observed six cases of natural death, three cases of accidental death, and one that was unknown (Table 13). Most deaths in this category were classified as natural deaths, and in many cases, the bereaved families requested that an autopsy be performed.


Autopsies performed in compliance with the Investigation Act

In 2022, there were 16 autopsies performed in compliance with the Investigation Act ― a relatively modest number. In addition to the International University of Health and Welfare, Nippon Medical School, which was relocated to Chiba Prefecture, also handled these autopsies. This collective effort marked a certain increase in the number of autopsies performed in the Chiba Prefecture as a whole. Nine of the 16 autopsies were on men and seven on women; their ages ranged from 37 to 92 years, and the mean and median ages were 69 and 74 years, respectively. Regarding the manner of death, most deaths were attributed to natural causes, followed by accidental death (Table 14). Although the cases did not require judicial autopsies, we assumed the autopsy had been performed in certain instances to confirm the cause of death.


Child deaths

In 2022, autopsies were performed on 9 children (aged <18 years) or infants. Among these, eight autopsies were judicial and one was administrative. Two deaths were attributed to natural causes, three to accidents, one to suicide, two to homicides, one to an undetermined external cause, and two to unknown causes. One of the unknown causes was sudden infant death and the other was a stillborn baby.


Novel coronavirus

The outbreak of the new coronavirus disease (COVID-19) continued into 2022 and had a major impact on the practice of forensic medicine. At Chiba University, PCR and antigen tests were conducted as in the previous year, and efforts were made to identify the cause of death and ensure the safety of the staff. In addition, there was one case in which COVID-19 was the underlying cause of death as determined by autopsy. However, there were also cases in which side effects after vaccination were suspected, but the cause of death could not be determined.


CT examinations

CT examinations without autopsies were performed on 24 corpses in 2022. However, CT examinations were performed prior to the autopsies, including judicial autopsies, administrative autopsies, and autopsies under the Investigation Act, in all corpses. In addition, about 80 readings were performed, including individual identification by images, readings of biomedical images related to clinical forensics, and readings of CT images taken at other institutions. Moreover, although it is still in the research stage, magnetic resonance imaging was also adopted.


Forensic odontology

Dental findings were collected and recorded in the appraisal reports for almost all forensic autopsies of unidentified bodies. In addition, based on a partnership agreement, we collected dental findings from unidentified corpses that had undergone forensic autopsies at the University of Tokyo (UT) and International University of Health and Welfare, together with the Department of Forensic Dentistry, Tokyo Medical and Dental University. A case study meeting was held twice a year under a comprehensive partnership agreement with the Chiba Dental Association. In the child guidance center cases requested by our center, we performed intraoral evaluations in cases that required intraoral findings such as multiple dental caries and bite marks.


Forensic genetics

Regarding DNA testing, we received one request from the Japan Coast Guard as a commissioned source for judicial autopsies as well as DNA typing tests based on the request of the courts of law and nonofficial organizations. Moreover, because of the cooperation agreement between Chiba University and the UT, we performed DNA typing tests as requested by the UT, Tokyo District Public Prosecutors Office, and the Metropolitan Police Department.


Forensic toxicology

In addition to simple tests conducted on all bodies from which samples can be collected, drug toxicology tests using mass spectrometers (GC / MS, LC / MS / MS, LC / QTOF-MS) have also been implemented (qualitative analysis, quantitative analysis if necessary). Moreover, based on the cooperation agreement, we have been conducting drug and toxicology tests associated with autopsies performed at the UT. The main drugs detected at Chiba University in 2022 are presented in Table 15. Stimulants-related cases are not in the Top 10, but both Amphetamine and Methamphetamine were detected in 7 cases, indicating a sustained prevalence.


Clinical forensic medicine

At the request of child consultation centers in Chiba Prefecture, Chiba City, and Edogawa Ward, we submitted 52 written opinions related to child abuse and domestic violence. In addition, we received and responded to 23 consultations on injury cases from the Chiba District Prosecution and Chiba Prefectural Police, among others. In July 2018, a clinical forensic outpatient department was opened within the pediatrics division of Chiba University Hospital. Both the hospital’s pediatrics department and the forensic department cooperated to enhance the examination system. With the cooperation of other specialized departments, we aim to ascertain injuries caused by abuse, among other causes.


Chiba CDR

Every year, we hold the Chiba Child Death Review (CCDR), and experts in Chiba Prefecture, including pediatricians, government officials, and the judiciary, share information on child death cases and hold discussions on how to prevent their recurrence. On February 19th, 2022, we hosted the 15th meeting, marking the first session after an interval of about two years. After discussing the origins of the CDR system, the current situation in Japan, and the background and future of this study group, a case study was conducted. Although the event was held amid concerns about the impact of the new coronavirus, about 100 people, including members of the Chiba prefectural assembly, attended the event after dispersing the venue.


Disaster victim identification training

Although we conduct training to prepare for large-scale disasters (DVI: Disaster Victim Identification) every year, due to the restrictions caused by the COVID-19 crisis, we could not hold DVI training in 2021 and 2022. Yet, in fiscal year 2022, we facilitated various disaster trainings for nine prefectures and cities, and we validated the activities in the event of a disaster. At our facility, we cooperated with IUHW to prepare the training during the non-pandemic season.