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.

Compared with the 412 autopsies performed at Chiba University in 2019, the total number of autopsies performed in 2020 was 308. Both the number of judicial autopsies and autopsies performed in compliance with the Death Investigation and Identification Act (hereafter “the Investigation Act”) were significantly reduced. This was the third lowest number of autopsies performed in the last decade. This tendency did not change in Chiba prefecture as a whole, even with the impact of the new coronavirus pandemic. Considering the decrease in the number of deaths and the fact that the national trend in forensic autopsies has decreased slightly, it is not clear why Chiba prefecture has experienced this outcome. However, such a large change in autopsy numbers from one year to the next indicates an instability in Japan's death investigation system.

The Basic Act for the Promotion of Death Investigation was enforced in April 2020. 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 plan had been declared previously, and we could not see expected the new measures. We hope that effective reform policies will be developed in the future.

We not only collect relevant information on dead people, determine the exact cause of death of each individual, and identify bodies; we also clarify the death trends in Japan and help prevent accidents and disasters, as well 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 through providing information on the causes of death, and we hope to contribute to system improvements through 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 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 5 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 the direct cause of death, such as drowning.



In 2020, the population of Chiba Prefecture was approximately 6,280,000. A total of 62,164 deaths were reported in this prefecture. Overall, 9,166 deaths were reported to the police department, 8,968 to detectives, and 198 to the Traffic Bureau. A total of 331 judicial autopsies were performed. This represents a 24.6% decrease compared with the previous year. In all, 324 were managed by the police department, 299 by detectives, 25 by the Traffic Bureau, 4 by the Coast Guard (Chiba and Katsuura), and 3 by Chiba District Prosecution. Among all autopsies performed during this year, 9 were administrative autopsies. In compliance with the Investigation Act, 15 autopsies were performed. The total number of medicolegal autopsies was 377 and the autopsy rate per death was approximately 0.6%. Compared with 2019, the total number of autopsies decreased by 23.7%.

Overall, 308 medicolegal autopsies were performed at our center in 2020. This represented a 25.2% decline compared to the previous year. These autopsies included 306 judicial autopsies, 9 administrative autopsies, and 15 autopsies performed in compliance with the Investigation Act. Among the judicial autopsies, 279 were commissioned by the Chiba Prefectural Police (262 by detectives and 17 by the Traffic Bureau) 4 by the Chiba District Prosecution, and 5 by the Ibaraki Prefectural Police Department. We performed two postmortem examinations using computed tomography (CT).

In fiscal year 2018, the forensic pathologists in the center began to perform some services under the jurisdiction of the Chiba Central Police Office instead of physicians. They performed 21 postmortem examinations in 2020. The number of these services has been increasing each year.

Regarding laboratory examinations, drug and poison tests, pathology organization inspection, blood typing, blood biochemical tests, and other tests, as required, were performed in all corpses, 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 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 a police was conducted at the crime laboratory, so there was no request for this service from the Chiba Prefectural Police. In addition to the requests from the Coast Guard, we incorporated in 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.

In previous years, we have held “Chiba Child Death Reviews (Chiba CDR)” several times with pediatricians, other physicians, government, and judicial officials in the prefecture. We organized these reviews to share information on the causes of death in children and to discuss preventive measures. However, in 2020 we held only one such review due to the new coronavirus pandemic.


Judicial autopsies

In 2020, judicial autopsies were performed on 284 corpses. The details are outlined in the following tables.

Table 1 shows the nationality of the corpses managed by our center in 2020. We identified nine corpora of foreign nationals in four areas.

Table 2 shows the manner of death of all the corpses managed by our center. We recorded 56 (20%) natural deaths, 79 (28%) accidents, 59 (21%) suicides, 18 (6%) homicides, 27 (10%) deaths associated with undetermined external causes, and 45 (16%) deaths were associated with an unknown cause. In 2020, we observed a lower rate of accidental deaths than the average number of deaths in previous years. Overall, the fatality rate was approximately 2.1-fold higher in men than in women and men outnumbered women in all manner of death.

Table 3 shows the age distribution of the corpses managed by our center. The total number of individuals aged >65 years was less than 50%. This suggests a decline in the percentage of older individuals. The mean and median ages were 59 and 61 years, respectively. The mean age based on the cause of death was 48 years in cases of suicide, 54 years in cases of homicide, 65 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. Evaluation of the number of cases by month showed that most deaths occurred between October and January.

Tables 5 and 6 show the causes of natural death. Although the number of deaths was too low to accurately describe results, the causes of natural death were like those contributing to the overall mortality statistics of the population (heart disease, cerebrovascular disease, malignant neoplasm, and pneumonia). In addition, there were many behavioral disorders due to drinking, such as chronic alcoholic poisoning. We observed that 50% of deaths attributable to natural causes occurred in those aged >64 years.

Tables 7 and 8 list the causes of accidental deaths. In 2020, fires were observed to be the leading cause of death followed by traffic accidents and other accidents. Many other accidental deaths were attributed to heat stroke, hypothermia, and work-related deaths. These did not meet the criteria for a specific category. More than half of the deaths associated with fires occurred in individuals aged >74 years. This was 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 were hanging followed by drowning. This is similar to the statistics of the National Police Agency. We identified some cases of drowning associated with an undetermined external manner. These deaths could not be clearly classified as suicides. Drugs and poisoning accounted for more deaths than the average of previous years. As for gender, there were as many men as usual, however the difference between the genders was smaller than in the previous year. Although we observed that suicidal deaths were distributed across all age groups, suicide among young people was prominent in 2020.

Tables 11 and 12 list the homicidal deaths recorded in 2020 and the methods used. Although there were more female victims in previous years, in 2020 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 distributed across all age groups.


Administrative autopsies

Among the 9 corpses on which autopsies were performed for administrative purposes, 5 were men and 4 were women. Their ages ranged from 25 to 77 years. The mean and median ages were 52 and 55 years, respectively. We observed 7 cases of natural death and 2 cases 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

Compared with the 70 autopsies performed in 2018 and the 40 autopsies in 2019, the number performed decreased to 15 in 2020. Among these, 7 were men and 8 were women. Their ages ranged from 1 to 89 years and the mean and median ages were 55 and 51 years, respectively. Regarding the manner of death, most deaths were attributed to natural causes, followed by suicide (Table 14). Although the cases did not require judicial autopsies, there were certain cases in which we assumed the autopsy was carried out to confirm the cause of death.


Child deaths

In 2020, autopsies were performed on 11 children (aged <18 years) or infants. Among these, 9 autopsies were judicial, and 2 were in compliance with the Investigation Act. Two deaths were attributed to natural causes, 2 to accidents, 1 to suicide, 2 to homicides, 1 to an undetermined external cause, and 3 to undetermined causes. One of homicidal deaths was caused by child abuse, and the other was the death followed by suicide. One of the deaths attributed to an undetermined cause was categorized as sudden infant death at the age of 1. In the other 2 cases, newborns died.


CT examinations

CT examinations without autopsies were performed on 3 corpses in 2020, 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. Moreover, although it is still at the research stage, magnetic resonance imaging was also performed.


Forensic odontology

Based on the request of Chiba Prefectural Police and the Coast Guard, we conducted dental examinations to identify the bodies. With the absence of formal request, we examined the teeth of all other unidentified bodies. And, because of 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 in 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 to our center.


Forensic genetics

We performed DNA typing tests based on the request of the Coast Guard, 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.


Forensic toxicology

The main drugs detected in 2020 are presented in Table 15. Detection of stimulants was prominent in 2020.


Chiba CDR

We held the 14th meeting of the Chiba CDR at Keisei Hotel Miramare on January 26, 2020. Two experts furnished presentations on the current situation and future prospects of the CDR system. The system has gained a legal basis and has initiated model projects. We discussed this issue. Subsequently, we reviewed cases of accidental death in infants.

We held the meeting only once in 2020.

Disaster victim identification training

We could not conduct DVI training in 2020 due to the restrictions caused by the coronavirus crisis.