Using accumulated degree-days to estimate the postmortem interval from decomposed human remains

Forensic anthropologists often rely on the state of decomposition to estimate the postmortem interval (PMI) in a human remains case. The state of decomposition can provide much information about the PMI, especially when decomposition is treated as a semi-continuous variable and used in conjunction with accumulated-degree-days (ADD). This preliminary study demonstrates a supplemental method of determining the PMI based on scoring decomposition using a point-based system and taking into account temperatures in which the remains were exposed. This project was designed to examine the ways that forensic anthropologists could improve their PMI estimates based on decomposition by using a more quantitative approach. A total of 68 human remains cases with a known date of death were scored for decomposition and a regression equation was calculated to predict ADD from decomposition score. ADD accounts for approximately 80% of the variation in decomposition. This study indicates that decomposition is best modeled as dependent on accumulated temperature, not just time.     

The Influence of Preburial Insect Access on the Decomposition Rate

Abstract: This study compared total body score (TBS) in buried remains (35 cm depth) with and without insect access prior to burial. Sixty rabbit carcasses were exhumed at 50 accumulated degree day (ADD) intervals. Weight loss, TBS, intra‐abdominal decomposition, carcass/soil interface temperature, and below‐carcass soil pH were recorded and analyzed. Results showed significant differences (p << 0.001) in decomposition rates between carcasses with and without insect access prior to burial. An approximately 30% enhanced decomposition rate with insects was observed. TBS was the most valid tool in postmortem interval (PMI) estimation. All other variables showed only weak relationships to decomposition stages, adding little value to PMI estimation. Although progress in estimating the PMI for surface remains has been made, no previous studies have accomplished this for buried remains. This study builds a framework to which further comparable studies can contribute, to produce predictive models for PMI estimation in buried human remains.     

Potential Use of Bacterial Community Succession in Decaying Human Bone for Estimating Postmortem Interval,,

Bacteria are taphonomic agents of human decomposition, potentially useful for estimating postmortem interval (PMI) in late‐stage decomposition. Bone samples from 12 individuals and three soil samples were analyzed to assess the effects of decomposition and advancing time on bacterial communities. Results indicated that partially skeletonized remains maintained a presence of bacteria associated with the human gut, whereas bacterial composition of dry skeletal remains maintained a community profile similar to soil communities. Variation in the UniFrac distances was significantly greater between groups than within groups (p < 0.001) for the unweighted metric and not the weighted metric. The members of the bacterial communities were more similar within than between decomposition stages. The oligotrophic environment of bone relative to soft tissue and the physical protection of organic substrates may preclude bacterial blooms during the first years of skeletonization. Therefore, community membership (unweighted) may be better for estimating PMI from skeletonized remains than community structure (weighted).     

Measuring Desiccation Using Qualitative Changes: A Step Toward Determining Regional Decomposition Sequences

The creation of a regional decomposition scoring system for western Colorado provides a model for the creation of regional systems. The development of a scoring system requires: (1) human remains, not proxies, (2) longitudinal observations, and (3) large sample size. First, an enhanced system (total body desiccation score; TBDS) was developed through observations of 40 human remains. This effort produced a categorical scoring model augmented by qualitative categories of gross tissue change. The new model was tested with retrospective photographic packets. A sample of eight donors with data collected over 3 years was selected. Monthly data points over a maximum of a 3‐year period yielded 112 data points. Correlations between TBDS and accumulated degree‐days (ADD), and total body score (TBS) and ADD were approximately equal for a TBS below ~20, but the TBDS correlated better with ADD at higher TBS scores >20. The TBDS may be used to refine postmortem interval (PMI) models in areas where remains desiccate.     

Estimation of postmortem interval (PMI) as revealed through the analysis of annual growth in woody tissue

The discovery of human remains lying across a black spruce (Picea mariana) leader (branch) that subsequently grew up around the remains provided an opportunity to use the growth ring pattern to estimate the postmortem interval (PMI). As these remains were discovered in an advanced state of decomposition in October of 2000, and it was clear that relevant insect evidence was not forthcoming, this novel approach to estimating PMI was proposed. The asymmetrical growth of the leader resulted in a correspondingly asymmetrical pattern of its growth riings. As the date of cutting the leader was known, it was possible to evaluate the asymmetrical growth pattern to provide an estimation of PMI. Fine polishing of the cross section and computerized quantification of ring widths enabled an estimation of the displacement of the leader, and hence the time the decedent's body was so positioned. By charting the ring-width differential for the leader, it was concluded that the displacement occurred sometime between July of 1993 and May of 1994. The actual date of disappearance was confirmed to be August 24, 1993.     

Use of beetles in forensic entomology.

Beetles (Coleoptera) have been recognised as providing significant entomological evidence in the medico-legal field, particularly with reference to dry human skeletal remains in the later stages of decomposition.The Dermestidae (skin beetles) and Cleridae (bone beetles) have been found as the most common types infesting exposed human remains and providing evidence in estimating the minimum postmortem interval (PMI).     

Post-mortem interval estimation using miRNAs of road traffic accident cases: A forensic molecular approach

In forensic examination accurate estimation of post-mortem interval (PMI) is a challenging task, particularly in the advanced stages of decomposition. The existing methods (algor mortis, livor mortis, rigor mortis, putrefaction etc) used for estimating PMI rely on analyzing the physical, biochemical, and metabolic changes that occur in the corpse after death. While these methods have shown some level of effectiveness in estimating PMI during the early stages of decomposition, accurate estimation becomes increasingly challenging during the later stages of putrefaction when the body undergoes significant changes. Recently, microRNA (miRNA) profiling due to its relatively small size and stability has emerged as a promising tool in several areas of forensics. This study demonstrates the potential of miRNA for PMI estimation in advanced stages of death. In this study, miRNA-195, miRNA-206, and miRNA-378 were selected as target miRNAs and miRNA-1 as reference miRNA. Left ventricle tissue (5 g) of the heart from 20 forensic autopsies of traffic accident victims (18–32 years) were collected and processed. The samples were held at room temperature for eight different time intervals (12, 24, 48, 72, 96, 120, 168 and 196 h), and RNA was extracted from all the samples using Trizol-based RNA isolation protocol, followed by cDNA synthesis and amplification with commercially available specific miRNA probes in Real-Time PCR (RT-PCR), Ct was calculated. The result showed that miRNAs were associated with PMI. Over time, there were substantial changes in the Ct values of all three miRNAs, with significant reductions observed at 196 h compared to 12 h. miRNA-206 demonstrated significant changes at multiple time intervals, while miRNA-1 remained stable for up to 196 h and thus holds caas an endogenous marker. In conclusion, miRNA has the potential to serve as a valuable tool for estimating PMI, especially during the advanced stages of decomposition, when used in conjunction with established techniques. However, further validation of the study is required to obtain more accurate estimates of PMI.     

Application of the hexagon-OBTI test and the RSID blood test for the determination of the post-mortem interval of bone samples

In this serial experiment, five human bones with known post-mortem intervals (PMI) in a soil environment from five different epochs (0.2 to approximately 2000 years) were tested in a blind setup with two established rapid tests for the identification of human blood traces (Hexagon-OBTI test and RSID blood test). Based on previous study results concerning the usability of the Luminol test for the first assessment of the PMI of osseous remains, the question arising was whether those test procedures, which are highly sensitive for the detection of human blood components, could also be used to narrow down the post-mortem interval. Five test series were conducted applying modified standard protocols of the manufactures. The aim was to find out whether with prior reaction steps or a prolonged time of incubation hemoglobin or its metabolites can be dissolved from the bone and positive test results can be achieved dependent on the PMI. Four test series yielded negative results for all bone samples and one test series a uniformly weak positive result. The results indicate that rapid tests based on the detection of blood are not suitable for the determination of the PMI of bone samples despite the modification of the standard protocols. Further thorough research is required to clarify the postmortem degradation of hemoglobin in bones.     

A Longitudinal Study on Human Outdoor Decomposition in Central Texas

The development of a methodology that estimates the postmortem interval (PMI) from stages of decomposition is a goal for which forensic practitioners strive. A proposed equation (Megyesi et al. 2005) that utilizes total body score (TBS) and accumulated degree days (ADD) was tested using longitudinal data collected from human remains donated to the Forensic Anthropology Research Facility (FARF) at Texas State University‐San Marcos. Exact binomial tests examined the rate of the equation to successfully predict ADD. Statistically significant differences were found between ADD estimated by the equation and the observed value for decomposition stage. Differences remained significant after carnivore scavenged donations were removed from analysis. Low success rates for the equation to predict ADD from TBS and the wide standard errors demonstrate the need to re‐evaluate the use of this equation and methodology for PMI estimation in different environments; rather, multivariate methods and equations should be derived that are environmentally specific.     

Postmortem interval of skeletal remains through the detection of intraosseal hemin traces. A comparison of UV-fluorescence, luminol, Hexagon-OBTI®, and Combur® tests

With the goal of obtaining additional practically applicable methods for estimating the PMI of skeletal remains, 39 samples of human and 5 samples of domestic animal long bones with known PMI (PMI=1 to approximately 2000 years) were tested with two established methods (UV-fluorescence of a freshly sawn cross-section and the luminol test) and two screening tests (Hexagon-OBTI? test and Combur? test) that were being tried out in this context for the first time. The hypothesis underlying this experiment was the supposition that the PMI-related chemiluminescence of the luminol reaction for bone is based on the presence of persisting hemin from hemoglobin molecules in bone. Our results showed that lack of luminescence and reduced UV-fluorescence were more meaningful results for estimating PMI and excluding forensic relevance than a positive luminol reaction or strong UV-fluorescence, as both of the latter findings revealed the limitations of these methods in this particular context. Particularly for cases showing a positive luminol reaction, the use of additional absolute dating methods may be indicated. Against our expectations, both the Combur? test strips and the Hexagon-OBTI? test, which were both devised to demonstrate blood, delivered negative results for all samples. They are thus not suitable for estimating the PMI of skeletal remains. Future research will be necessary to elucidate whether the negative results obtained for these tests may be due to the poor solubility of potentially present hemoglobin or hemoglobin breakdown products in the Tris buffer used in this experiment.     

The application of geographic information systems and spatial analysis to assess dumped and subsequently scattered human remains

This study utilizes geographic information systems (GIS) and spatial analysis (SA) technology to address the problems associated with prediction of location and effective recovery of dumped and scattered human remains in Louisiana. The goals are to determine if a selective bias exists in Louisiana as to where and when human remains are dumped and to assess whether or not geographically specific patterns exist in the dispersal of human remains. We hypothesized that a positive relationship exists between postmortem interval (PMI) and dispersal distance, and that there are negative relationships between PMI and dispersal direction and between dispersal direction and distance. Our results indicate that, in Louisiana, remains are more often dumped in rural areas away from a structure, and are found within (1/4) mile of the nearest road. For Louisiana, no seasonal bias was found in the analysis of when remains are dumped. Furthermore, with the exception of the relationship between PMI and the shortest distance remains were dispersed, no geographically specific patterns were detected in the analyses of dispersal distance, dispersal direction, and PMI.     

人脾细胞核几何参数变化与早期死亡时间的相关性研究

目的运用图像分析技术探讨人脾脏细胞核几何参数变化与死亡时间的关系。方法选31例已知死亡时间的人离体脾组织,在死后36h内每h细胞学涂片、Feulgen-Vans染色,对人脾细胞核的异形指数等5个几何参数进行图像分析。结果脾脏细胞核异形指数在死后5～36h呈上升趋势,r=0.983,线性回归方程y=11.334x-33.339,面积、等效直径、平均直径、周长均与死亡时间无明显的相关性。结论异形指数能较客观地反映人脾细胞核DNA降解后的离散分布状况,与死亡时间有明显相关性,可能是推断早期准确死亡时间的较好形态学指标。     

Mapping the lateral extent of human cadaver decomposition with soil chemistry

Soil below decomposing cadavers may have a different lateral spatial extent depending upon whether scavengers have access to the human cadaver or not. We examined the lateral spatial extent of decomposition products to a depth of 7cm of soils beneath two decomposing corpses, one in which the subject was autopsied, unclothed and placed under a wire cage to restrict scavenger access and one in which the subject was not autopsied, unclothed and exposed to scavengers. The two bodies had accumulated degree days (ADD) of 5799 and 5469 and post mortem interval (PMI) of 288 and 248d, respectively. The spatial extent for dissolved organic carbon (DOC) and organic nitrogen (DON) for both bodies was large but similar suggesting some movement off site for both compounds. Mean DOC was 1087±727 and 1484±1236μgg(-1) dry soil under the two corpses relative to 150±68μgg(-1) in upslope control soils. Sulfate tended to have 'hot spots' of lower values relative to the control soils indicative of anaerobic respiration. pH was lower and electrical conductivity was higher in the soil under both decomposing cadavers relative to control soils. Some of the nutrients examined downslope of the human remains were significantly higher than control soils upslope suggesting movement of decomposition products off-site which could be an important factor when using human remains detector dogs.     

A retrospective comparative study to evaluate the reliability of post-mortem interval sources in UK and US medico-legal death investigations

Post-mortem interval (PMI) information sources may be subject to varying degrees of reliability that could impact the level of confidence associated with PMI estimations in forensic taphonomy research and in the practice of medico-legal death investigation. This study aimed to assess the reliability of PMI information sources in a retrospective comparative analysis of 1813 cases of decomposition from the Allegheny County Office of the Medical Examiner in Pittsburgh, US (n = 1714), and the Crime Scene Investigation department at Southwest Forensics in the UK (n = 99). PMI information sources were subjected to a two-stage evaluation using an adapted version of the 3x5 aspects of the UK police National Intelligence Model (NIM) to determine the confidence level associated with each source. Normal distribution plots were created to show the distribution frequency of the dependent variables (decomposition stage and source evaluation) by the independent variable of PMI. The manner, location, and season of death were recorded to ascertain if these variables influenced the reliability of the PMI. A confidence matrix was then created to assess the overall reliability and provenance of each PMI information source. Reliable PMI sources (including forensic specialists, missing persons reports, and digital evidence) were used across extensive PMI ranges (1 to 2920 days in the US, and 1 to 240 days in the UK) but conferred a low incidence of use with forensic specialists providing a PMI estimation in only 35% of all homicide cases. Medium confidence PMI sources (e.g., last known social contact) accounted for the majority of UK (54%, n = 54) and US (82%, n = 1413) cases and were associated with shorter PMIs and natural causes of death. Low confidence PMI sources represented the lowest frequencies of UK and US cases and exclusively comprised PMI information from scene evidence. In 96% of all cases, only one PMI source was reported, meaning PMI source corroboration was overall very low (4%). This research has important application for studies using police reports of PMI information to validate PMI estimation models, and in the practice of medico-legal death investigation where it is recommended that i) the identified reliable PMI sources are sought ii) untested or unreliable PMI sources are substantiated with corroborating PMI information, iii) all PMI sources are reported with an associated degree of confidence that encapsulates the uncertainty of the originating source.     

A New Method for Determination of Postmortem Interval: Citrate Content of Bone*

Abstract: Few accurate methods exist currently to determine the time since death (postmortem interval, PMI) of skeletonized human remains found at crime scenes. Citrate is present as a constituent of living human and animal cortical bone at very uniform initial concentration (2.0 ± 0.1 wt %). In skeletal remains found in open landscape settings (whether buried or not), the concentration of citrate remains constant for a period of about 4 weeks, after which it decreases linearly as a function of log(time). The upper limit of the dating range is about 100 years. The precision of determination decreases slightly with age. The rate of decrease appears to be independent of temperature or rainfall but drops to zero for storage temperature <0°C.     

嗜尸性甲虫在尸体上的演替及其法医学应用前景

作为法医昆虫学的主要研究对象之一,嗜尸性甲虫在腐败晚期干化和白骨化尸体的死亡时间推断中具有双翅目昆虫所无法取代的重要意义,并对尸体的腐败、破坏、分解和姿势改变发挥着不容忽视的作用。本文阐述了嗜尸性甲虫在尸体上的演替,分析了嗜尸性甲虫演替的影响因素,介绍了嗜尸性甲虫在法医学中的应用和前景。虽然目前对嗜尸性甲虫的研究还很少,但嗜尸性甲虫在法医鉴定中的作用将在今后受到越来越多法医工作者的重视。     

人体死后肝细胞DNA含量与死亡时间关系的研究

目的研究人体死后肝脏细胞DNA含量变化与死亡时间的关系及影响因素。方法选取46例已知死亡时间的人体肝脏,根据离体肝脏所处的环境温度分为12—19％（A组）和20—27％（B组）两组,每组23例。在死后24～72h内每隔4h穿刺取肝组织1次,制成细胞悬液,经RNA酶消化,PI染色后,用流式细胞仪测定被检测细胞中含不完整DNA的细胞数所占百分比,所得数据经Exp032V1．2软件计算N值。结果死后24～72h肝细胞N平均值,A组从10．91％增至49．72％,B组从16．22％增至69．63％。两组N平均值随死亡时间的延长均逐渐增高,与死亡时间有相关性,A组r值为：0．598,B组r值为0．77357。并且建立了不同环境温度对应的回归方程。结论在不同环境温度下,死后24～72h内人体肝脏细胞DNA降解均随死亡时间的延长和环境温度的升高而逐渐加快,相关数据可望为死亡时间推断提供一定参考依据。     

Citrate Content of Bone as a Measure of Postmortem Interval: An External Validation Study

The postmortem interval (PMI) of skeletal remains is a crucial piece of information that can help establish the time dimension in criminal cases. Unfortunately, the accurate and reliable determination of PMI from bone continues to evade forensic investigators despite concerted efforts over the past decades to develop suitable qualitative and quantitative methods. A relatively new PMI method based on the analysis of citrate content of bone was developed by Schwarcz et al. The main objective of our research was to determine whether this work could be externally validated. Thirty‐one bone samples were obtained from the Forensic Anthropology Center, University of Tennessee, Knoxville, and the Onondaga County Medical Examiner's Office. Results from analyzing samples with PMI greater than 2 years suggest that the hypothetical relationship between the citrate content of bone and PMI is much weaker than reported. It was also observed that the average absolute error between the PMI value estimated using the equation proposed by Schwarcz et al. and the actual (“true”) PMI of the sample was negative indicating an underestimation in PMI. These findings are identical to those reported by Kanz et al. Despite these results this method may still serve as a technique to sort ancient from more recent skeletal cases, after further, similar validation studies have been conducted.     

Developing a new scoring method to evaluate human decomposition in a humid,continental (Dfb) climate in Quebec

The published literature shows a lack of methods to evaluate the patterns and extent of decomposition of human remains and to estimate the post-mortem interval (PMI) in humid, continental (Dfb) climates such as Quebec. The aim of this study was to address this gap in the current knowledge base by providing the first observations from human corpses studied under controlled conditions in Quebec. A 12-month study was conducted at the site for Research in Experimental and Social Thanatology; the first human taphonomy facility in Canada. Six human donors with known time of death were deposited across spring (n = 1), summer (n = 3), and autumn (n = 2) 2021. The lack of suitability of the total body score method to evaluate the extent of decomposition at the facility prompted the development of a new scoring system based on the macromorphoscopic changes observed. The scoring system was applied to the donors to evaluate decomposition throughout seasons. All donors followed comparable decomposition trajectories, regardless of the season of deposition. Eighty-five percent of taphonomic patterns appeared in the first 25 experimental days or 5000 Kelvin accumulated degree days (350 ADD). Extensive desiccation of tissues was observed at a median of 21 experimental days across donors, resulting in a plateau within decomposition with no extensive skeletonization. To the authors' knowledge, this is the first published report of experimentally observed desiccation in such a form in a Dfb climate. This study provides new data on the types of decomposition patterns to expect in forensic investigations in southern Quebec and comparable climates.