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 and prosecution teams regarding live individuals and then conduct forensic diagnoses.

In 2016, there were 30 fewer autopsies performed compared to 2015, which was similar to the reduction in autopsies performed between 2015 and 2014. In particular, 36 fewer judicial autopsies were performed, despite no equivalent reduction rate throughout Japan. The total number of medicolegal autopsies in Japan had marked a small increase compared to 2015, due to a greater number of autopsies required in accordance with the new Death Investigation and Identification Act. As the number of autopsies undertaken in compliance with the new Act depends on the financial situation of local governments, and in the Chiba Prefecture there is no prospect of a large budget increase to cover the need for increased expenditure concerning autopsies, we consider that the reduction of judicial autopsies will lead to a decrease in the total number of autopsies. This downward trend in autopsies has generated a crisis in relation to ongoing death investigations.

In June 2014, the Government of Japan implemented a program to promote death investigations. Prompted to act as result of this program, a committee dedicated to the promotion of death investigations in the Chiba Prefecture was established in March 2016. However, we had to wait a year for another meeting. Thus far, addressing issues related to death investigations has not been easy.

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, Labor 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, fall from a high place, 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 2016, the population of the Chiba Prefecture was approximately 6,240,000; there were 56,079 deaths. The number of bodies reported to the police was 7,758 (7,478 to detectives and 280 to the traffic bureau). There were 288 judicial autopsies: 276 handled by the police (244 by detectives and 32 by the traffic bureau), 9 by the Coast Guard (Chiba and Choshi), 2 by the Defense Army and 1 by the Chiba District Prosecution. There were 14 administrative autopsies. Twenty-two autopsies were performed in compliance with the new Act. The overall medicolegal autopsy rate was approximately 0.6%. Compared with the previous year, there was a decrease of 23 (9.2%) in the total number of autopsies (324).

In our Center, we performed a total of 304 medicolegal autopsies in 2016, including 268 judicial autopsies, 14 administrative autopsies, and 22 autopsies in compliance with the new Act. Of the judicial autopsies, 292 were commissioned by the Chiba Prefectural Police (220 by detectives and 27 by the traffic bureau), 9 by the Coast Guard (Chiba and Choshi), 2 by the Defense Army, 1 by the Chiba District Prosecution, and 9 by the Ibaraki Prefectural Police. We performed 17 postmortem examinations using computed tomography (CT).

Regarding laboratory examinations, drug and poison tests, pathology organization inspection, blood typing, blood biochemical tests, and other tests as may be needed are performed on all corpses from which a specimen can be obtained. Where needed, we examine bodies for signs of carbon monoxide poisoning and the presence of plankton and sperm. We first perform CT imaging studies, after which we perform the autopsy, obtain the various test results, investigate the dead person’s situation, and comprehensively estimate the cause and manner of death. Following a cooperation agreement between Chiba and Tokyo University, we perform drug and poison tests at Tokyo University. With respect to the services of forensic odontology and forensic genetics, we confirm the identity of unidentified remains using dental records and DNA testing.

Regarding clinical forensic medicine, 2016 was the fourth year in operation since service implementation. We received 43 requests from child consultation centers in Chiba Prefecture and Chiba City, Chiba Prefectural Police, and Chiba District Prosecution, and conducted forensic diagnoses accordingly.


Judicial autopsies

Table 1. shows the nationality of the corpses. There were 11 foreign corpses from 8 countries, which were all of Asian origin.

Table 2. indicates the manner of death. There were 28 (10%) natural deaths, 90 (34%) unexpected accidents, 37 (14%) suicides, 29 (11%) homicides, 28 (10%) deaths through undetermined external causes, and 56 (21%) deaths that occurred for unknown reasons. In 2016, the number of natural deaths was less than the average in comparable years. Overall, there were approximately 2.7 times more male than female fatalities. Many more males than females died due to the classified causes of death except homicide, which claimed more female victims than males.

Tables 3. and 4. indicate the age distribution of the corpses. Individuals older than 55 years of age accounted for 60% of all deaths, and the average age was 57 years. For the manner of death overall, the average age of homicide victims was the lowest, at 46 years. This is because many of the victims were children and young people. The average age of suicide victims was higher than in comparable years. There were no significant differences in the manner of death among the different calendar months, but fewer autopsies were required in May, June, and September.

Tables 5. and 6. indicate the causes of natural deaths. Although the number of deaths was too small to describe general tendencies, we found that approximately half of the natural deaths were due to circulatory diseases including heart disease, cerebrovascular disease and aortic dissection. Individuals aged 55 years and older accounted for 70%. However, those aged between 25 and 54 years tended to die suddenly from circulatory diseases.

Tables 7. and 8. indicate the causes of accidental deaths. In 2016, the leading cause was traffic accidents, followed with fire, which is a trend seen in comparable years. There were also accidental deaths due to heatstroke and hypothermia, and work-relate deaths, which do not fit within the precisely specified categories. More than two-thirds of deaths through fire occurred among people > 65 years of age, because they could not escape from the fire danger in time.

Tables 9. and 10. indicate the suicide methods. The most common means of suicide was drowning. In 2016, in terms of age, the people who died due to suicide were spread across all age groups, although in previous years younger people had been represented relatively more frequently.

Tables 11. and 12. indicate the homicide methods. Homicides involving death through strangulation, sharp force, and blunt force were common in 2016. A number of children aged < 15 years of age became victims in suicide-homicide cases and. Nevertheless, in 2016 more elderly people were killed than in comparable years.


Among deaths due to undetermined external causes (28 bodies), 17 died of drowning. Regarding the other cases, although we determined the direct causes of death, the manner of death (whether accident, suicide, or homicide) could not be determined.

Among the deaths that occurred for unknown reasons (56 bodies), it was difficult to identify the cause of death in 43 cases because of their bleached bones, corpse wax, mummification, or high degree of decomposition. In the remaining cases, we could determine neither internal nor external causes of death.

In 2016, autopsies were performed on 11 children or babies (18 years old and younger), among whom 1 died of natural causes, 6 from homicide, and 4 from undetermined causes. Among the 6 who died from homicide, 3 children were killed by 2 mothers (homicide-suicide). The 4 who died from undetermined causes died suddenly while sleeping.

Administrative autopsies

Among the 14 corpses on which autopsies were performed for administrative purposes, 13 were male and 1 was female. Their mean age was 51 years (range, 1 year to 86 years). There were 12 cases of natural death, 1 accidental death, and 1 undetermined cause of death. As in comparable years, most of the corpses autopsied in this category died from natural causes.


Autopsies performed in compliance with the Death Investigation and Identification Act (the new Act)

Among the 22 corpses autopsied, 18 were male and 4 were female. Their mean age was 53 years (range, 3 months to 97 years). There were 10 natural deaths, 5 accidental deaths, and 2 undetermined external causes of death, and 4 deaths from an undetermined cause.


CT examinations

CT examinations were performed on 17 corpses and we performed a subsequent autopsy on 10 of the corpses. . CT examinations were conducted prior to the autopsy in all cases.


Forensic odontology

On the request of the Coast Guard, we carried out dental examinations to identify bodies. Because of the cooperation agreement between Chiba and Tokyo Medical and Dental University, we are cooperative with the staff of the university in this regard. We also undertook dental examinations for many other corpses without a formal request.


Forensic genetics

We performed DNA typing tests at the request of the Coast Guard, law courts and nonofficial organizations. Moreover, because of the cooperation agreement between Chiba and Tokyo University, we performed DNA typing tests that the Tokyo District Public Prosecutors Office requested of Tokyo University.


Clinical forensic medicine

At the request of child consultation centers, we report the incidence of child abuse and domestic violence. In 2016, there were 25 cases. Additionally, the Chiba District Public Prosecutors Office and the Chiba Prefectural Police consulted us concerning 18 injury cases. We have submitted reports or answered the inquiries of each organization.