At the Education and Research Center of Legal Medicine, Chiba University, we perform autopsies and various tests on the deceased, mainly from the Chiba Prefecture, in cases where a law enforcement agency has identified the need for forensic investigation, and we determine the cause of death from a medical point of view. We also perform DNA tests and dental examinations to identify a body. Furthermore, we receive requests from child consultation centers, prosecution teams, and prefectural police regarding live individuals and then conduct forensic diagnoses.

The total number of autopsies performed in 2021 was 371__an increase of 63 compared with the 308 autopsies performed at Chiba University in 2020. Although the number of judicial autopsies, administrative autopsies, and autopsies performed in compliance with the Death Investigation and Identification Act (hereafter “the Investigation Act”) increased slightly, they did not reach the numbers of 2018 and 2019. Even considering the entry of the School of Medicine, International University of Health and Welfare in 2018, it is difficult to understand such changes in the number of autopsies when the number of deaths in Chiba Prefecture has been steadily increasing. This may indicate the instability of Japan’s death investigation system.

The Basic Act for the Promotion of Death Investigation was enforced in April 2020, and the Promotion Plan was decided upon by the Cabinet in June 2021. The 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.

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 discussion 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. We classify the cause of death as natural death, using the medium rank classification of the simple classification for the cause of death, based on vital statistics data obtained from the Ministry of Health, Labour and Welfare. We further classify accidental deaths into traffic accidents, falls, drowning, asphyxiation, fire, and other causes according to the results indicated on the corpse examination certificate. 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. Although many countries use five classifications for specifying the manner of death, here in Japan, where the manner of death for many unidentified bodies remains undetermined, we use the category “undetermined external death” for cases in which we do not know the manner of death but can determine its direct cause, such as drowning.



In 2021, the population of Chiba Prefecture was approximately 6,270,000. A total of 66,065 deaths were reported in this prefecture; overall, 9,166 deaths were reported to the police department, 9,139 to detectives, and 199 to the Traffic Bureau. A total of 432 judicial autopsies were performed__a 30.5% increase compared with the previous year. In all, 425 were managed by the police department, 408 by detectives, 17 by the Traffic Bureau, four by the Coast Guard (Chiba, Katsuura, and Choshi), and three by Chiba District Prosecution. Among all autopsies performed during this year, 14 were administrative autopsies. In compliance with the Investigation Act, 80 autopsies were performed, 79 were commissioned by the police department, and one by the Coast Guard. The total number of medicolegal autopsies was 526, and the autopsy rate per death was approximately 0.8% (the rate in Japan was approximately 1.5%.)

Overall, 371 medicolegal autopsies were performed at our center in 2021__an 18.8% increase compared to the previous year. These autopsies included 337 judicial autopsies, 14 administrative autopsies, and 20 autopsies performed in compliance with the Investigation Act. Among the judicial autopsies, 331 were commissioned by the Chiba Prefectural Police (318 by detectives and 13 by the Traffic Bureau), three by the Chiba District Prosecution, and three by the Ibaraki Prefectural Police Department.

In the fiscal year 2018, the forensic pathologists in the center__instead of physicians__began to perform some services under the jurisdiction of the Chiba Central Police Office. They performed 31 postmortem examinations in 2021. Apart from autopsies, forensic radiologists performed 21 postmortem examinations using computed tomography (CT).

Regarding 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, we examined the bodies for signs of carbon monoxide poisoning and the presence of plankton and sperm. First, we performed CT imaging studies; subsequently, we performed the autopsy, obtained various test results, investigated the dead person’s situation, and comprehensively estimated the cause and manner of death.

With respect to the services of forensic odontology and forensic genetics, we confirmed the identity of the 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 the crime laboratory; thus, the Chiba Prefectural Police did not request this service. In addition to the requests from the Coast Guard, we incorporated the testing of cases other than those in Chiba, according to the cooperation agreements with other universities.

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


Judicial autopsies

In 2021, judicial autopsies were performed on 337 corpses. The details are outlined in the following tables.

Table 1 shows the nationality of the corpses managed by our center in 2021. We identified eight corpora of foreign nationals in three areas. In addition, one case in Southeast Asia was identified in autopsies performed in compliance with the Investigation Act.

Table 2 shows the manner of death of all the corpses managed by our center. We recorded 57 (17%) natural deaths, 97 (29%) accidents, 56 (17%) suicides, 21 (6%) homicides, 44 (13%) deaths associated with undetermined external causes, and 62 (18%) deaths were associated with an unknown cause. Overall, the fatality rate was approximately 2.3-fold higher in men than in women, and men outnumbered women in all manners of death.

Table 3 shows the age distribution of the corpses managed by our center. The mean and median ages were 60 and 63 years, respectively, showing little difference from previous years. The mean age based on the cause of death was 49 years in cases of suicide, being a relatively lower age; 54 years in cases of homicide, which was older than in previous years; 68 years in cases of natural death; and 64 years in cases of accidental death.

Table 4 shows the monthly distribution of deaths based on the manner and number of deaths. No significant difference was found in the number of cases by month.

Tables 5 and 6 show the causes of natural death. Although the number of deaths was too low to accurately describe the results, the causes of natural death were like those contributing to the overall mortality statistics of the population (heart disease, malignant neoplasm, and cerebrovascular disease). In addition, many behavioral disorders were due to drinking, such as alcoholic ketoacidosis. We observed that more than half of deaths attributable to natural causes occurred in those aged >64 years.

Tables 7 and 8 list the causes of accidental deaths. In 2021, fires were observed to be the leading cause of death, followed by drowning and other accidental deaths. Although traffic accidents were one of the leading causes, in 2021, they were fewer. Many other accidental deaths were attributed to heat stroke, hypothermia, and work-related deaths, which did not meet the criteria for a specific category. More than 70% of the deaths associated with fires occurred in individuals aged >64 years, primarily because they were unable to escape the fire in time.

Tables 9 and 10 list the suicidal methods. The most common means of suicide was hanging, followed by drowning. The first means is similar to the statistics of the National Police Agency (however, the second mean of the nation was jumping from high places.) We identified some cases of drowning associated with an undetermined external manner, which could not be clearly classified as suicides. Suicides by carbon monoxide were frequent in 2021. As for sex, there were many males, as in previous years. Although we observed that suicidal deaths were distributed across all age groups, suicide among middle-aged people was prominent in 2021.

Tables 11 and 12 list the homicidal deaths recorded in 2021 and the methods used. The number was the same as in previous years. Although the average of the previous years showed more female victims, in 2021, the number was approximately the same for both men and women. As for the means of homicide, sharp force, strangulation, and blunt force were highly ranked. Homicidal deaths were usually distributed across all age groups; however, in 2021, many older persons >65 were killed. Cases included a homicide-suicide and a newborn corpse.

Among the 44 deaths that occurred secondary to undetermined external causes, 23 were attributed to drowning and three 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 62 deaths that occurred secondary to unknown causes, it was difficult to identify the cause of death in 56 cases due to bleached bones, corpse wax, mummification, or significantly decomposed corpses, including a case that was suspected to be suicide. Among the remaining cases, two involved the sudden death of infants.


Administrative autopsies

Among the 14 corpses on which autopsies were performed for administrative purposes, 12 were men, and two were women. Their ages ranged from 0 to 87 years. The mean and median ages were 45 and 47 years, respectively. We observed nine cases of natural death and one case of accidental death (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

The number of autopsies in this category was 20 in 2021. Although it was less than in 2018 and 2019, many autopsies were performed at the International University of Health and Welfare, and in Chiba Prefecture, the cases increased. Among these, 15 were men, and five were women; their ages ranged from 25 to 94 years, and the mean and median ages were 60 and 63 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 2021, autopsies were performed on 11 children (aged <18 years) or infants. Among these, nine autopsies were judicial, and two were administrative. One death was attributed to a natural cause, two to accidents, one to suicide, two to homicides, and five to undetermined causes. One homicidal death involved a newborn, and the other was a homicide-suicide. Four of the deaths attributed to an undetermined cause were categorized as sudden infant death.


Novel coronavirus

In 2021, the coronavirus disease 2019 (COVID-19) pandemic continued, with a great impact on forensic practice. At Chiba University, we conducted PCR and antigen tests and focused on identifying the cause of death and ensuring the safety of the staff. A total of 78 PCR tests were performed, two of which were positive. Antigen tests have been routinized since August 2021 and are performed on all cases for which samples can be collected. The total number of cases per year was 152, of which two were positive. As a result of the autopsy, the cause of death was COVID-19 in two cases. Conversely, two cases were of suspected side effects after vaccination (both administrative autopsies), but the cause of death could not be estimated.


CT examinations

CT examinations without autopsies were performed on 21 corpses in 2021. However, CT examinations were performed prior to the autopsies, including judicial autopsies, administrative autopsies, and autopsies under the Investigation Act, in all corpses. Radiologists in our center read the CT images. In addition, they also read 50 CT scans taken by other institutions. Moreover, although it is still at the research stage, magnetic resonance imaging was also adopted.


Forensic odontology

Based on the request of the Chiba Prefectural Police, we conducted dental examinations to identify the bodies. In the absence of a formal request, we examined the teeth of all other unidentified bodies, and following the cooperation agreement between Chiba University and Tokyo Medical and Dental University (TMDU), we worked together with the TMDU staff in this regard to conduct dental examinations of the bodies autopsied by the University of Tokyo (UT) and the International University of Health and Welfare (IUHW). Moreover, we conducted dental examinations of almost all cases requested by child consultation centers.


Forensic genetics

We performed 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, the Tokyo District Public Prosecutors Office, or the Metropolitan Police Department. In 2021, the Coast Guard made no requests.


Forensic toxicology

In addition to simple tests for all bodies from which samples can be collected, drug toxicology tests using mass spectrometers (GC / MS, LC / MS / MS, LC / QTOF-MS) have been conducted (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 and the TMDU. The main drugs detected at Chiba University in 2021 are presented in Table 15. The detection of stimulants was also prominent in 2021.


Clinical forensic medicine

At the request of child consultation centers in Chiba Prefecture, Chiba City, and Edogawa Ward, we submitted 60 written opinions related to child abuse and domestic violence. In addition, we received consultations on injury cases from the Chiba District Prosecution, Chiba Prefectural Police, etc., on a total of 23 cases and responded to each. In July 2018, a clinical forensic outpatient department was opened in the pediatrics department of Chiba University Hospital, and the pediatrics department of the hospital and the forensic department cooperated to enhance the examination system. With the cooperation of other specialized departments, we estimate 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 a recurrence. However, in 2021, such a review could not be held due to the spread of COVID-19.


Disaster victim identification training

Although we conduct training to prepare for large-scale disasters (DVI: Disaster Victim Identification) every year, we could not hold DVI training in 2021 due to the restrictions caused by the COVID-19 crisis.