Forensic Characteristics of Body Abandonment by Housemates in Japan

In Japan, many cases occur wherein housemates fail to report dead bodies found in their homes. However, only individual cases are reported through press and court records, and analysis including unreported cases has not been conducted. In this study, we evaluated cases handled by our Forensic Science Department in which housemates did not immediately report a dead body found in their home. We analyzed the overall picture and forensic characteristics of such cases, stratifying whether the abandoners were estimated hikikomori.

Of the 1,179 legal autopsy cases handled by the Department of Forensic Medicine of Tokai University from January 1, 2017, to July 1, 2023, we evaluated 45 cases in which housemates did not immediately report dead bodies. The characteristics analyzed were body age, cause of death, autopsy findings, duration from the body's discovery by the abandoner to the police report, the reason for the lack of report in the first body discovery by the abandoner, and the reason for the report. In this study, the criteria for estimating whether a hikikomori abandoned the body were (1) the police provided the information that the person was a hikikomori or (2) the person met the following four criteria: 20-64 years old, unemployed, not in school, and living with parents.

Positive significant differences were found in the body's decomposition and the time from the body's discovery to the report to the police when the abandoner was suspected to be a hikikomori for more than one, four, or eight days. No significant differences were found in the cause of death. Regarding the reported characteristics, when the abandoner was an estimated hikikomori, positive and significant differences were found for recognizing the body and did not report immediately due to shock. Conversely, negative and significant differences were found for the person who reported as the abandoner.

This is the first study that reports on body abandonment by housemates and elaborates on its complications to forensic doctors. The incidence rate of abandonment is higher than expected. This study suggests that hikikomori are more likely to hide the bodies for longer, which hinders the death cause investigation.