Comparative analysis of bones, mites, soil chemistry, nematodes and soil micro-eukaryotes from a suspected homicide to estimate the post-mortem interval

Criminal investigations of suspected murder cases require estimating the post-mortem interval (PMI, or time after death) which is challenging for long PMIs. Here we present the case of human remains found in a Swiss forest. We have used a multidisciplinary approach involving the analysis of bones and soil samples collected beneath the remains of the head, upper and lower body and “control” samples taken a few meters away. We analysed soil chemical characteristics, mites and nematodes (by microscopy) and micro-eukaryotes (by Illumina high throughput sequencing). The PMI estimate on hair 14 C-data via bomb peak radiocarbon dating gave a time range of 1 to 3 years before the discovery of the remains. Cluster analyses for soil chemical constituents, nematodes, mites and micro-eukaryotes revealed two clusters 1) head and upper body and 2) lower body and controls. From mite evidence, we conclude that the body was probably brought to the site after death. However, chemical analyses, nematode community analyses and the analyses of micro-eukaryotes indicate that decomposition took place at least partly on site. This study illustrates the usefulness of combining several lines of evidence for the study of homicide cases to better calibrate PMI inference tools.

针对疑似谋杀案件的刑事调查，需估算死后间隔时间（post-mortem interval，PMI），而对于长间隔PMI的估算颇具挑战性。本研究报道了一具在瑞士森林中发现的人类遗骸案例。本研究采用多学科研究方法，对遗骸头部、躯干上下部下方采集的骨骼与土壤样本，以及距遗骸数米外采集的“对照”样本开展分析：通过显微镜检测土壤化学特性、螨类与线虫，并借助Illumina高通量测序分析微真核生物。通过炸弹峰值放射性碳定年法对毛发的碳-14数据进行分析，得到的PMI估算范围为遗骸被发现前1至3年。针对土壤化学成分、线虫、螨类及微真核生物的聚类分析结果显示出两个类群：1）头部与躯干上部；2）躯干下部与对照样本。结合螨类证据，研究团队推断该遗骸大概率是在死后被搬运至该地点。然而，化学分析、线虫群落分析以及微真核生物分析结果表明，尸体分解至少有一部分是在该现场完成的。本研究表明，结合多维度证据开展谋杀案件研究，可更好地校准PMI推断工具，凸显了该方法的应用价值。