Estimation of day of death using micro-segmental hair analysis based on drug use history: a case of lidocaine use as a marker.

During investigations of unnatural death, the time of death is generally estimated using anatomical examinations. However, it can be difficult to accurately determine the day of death, because postmortem changes in the body tissues can be greatly affected by the circumstances of the location of the corpse. We recently developed a method to estimate the day of drug ingestion, using micro-segmental hair analysis based on internal temporal markers (ITMs). In this method, ITMs are ingested at a specific time interval before hair collection to mark timescales within individual hair strands. A single hair strand is segmented at 0.4-mm intervals, corresponding to average daily hair growth. The day of drug ingestion is eventually estimated by calculating the distances between segments containing the drug and ITMs in a hair strand. In the present study, the method was applied to estimate the day of death. A corpse was discovered with a documented medical history of lidocaine administration for surgery 57 days before the discovery. Micro-segmental analysis of a hair plucked from the corpse was performed using lidocaine as an ITM. Lidocaine was detected at specific regions in the hair strands. The day of death was estimated using the known surgery day, the distance from the hair root to the lidocaine peak in the hair strand, and the average hair growth rate. The novel estimation method using a hair enabled us to narrow the estimated time range of death up to the day of death, unlike the conventional anatomical examination. The micro-segmental hair analysis based on drug use history can be extremely helpful in determining the time of an unnatural death.