Late Postmortem Interval Research Articles

Enhancing late postmortem interval prediction: a pilot study integrating proteomics and machine learning to distinguish human bone remains over 15 years

BackgroundDetermining the postmortem interval (PMI) accurately remains a significant challenge in forensic sciences, especially for intervals greater than 5 years (late PMI). Traditional methods often fail due to the extensive degradation of soft tissues, necessitating reliance on bone material examinations. The precision in estimating PMIs diminishes with time, particularly for intervals between 1 and 5 years, dropping to about 50% accuracy. This study aims to address this issue by identifying key protein biomarkers through proteomics and machine learning, ultimately enhancing the accuracy of PMI estimation for intervals exceeding 15 years.MethodsProteomic analysis was conducted using LC–MS/MS on skeletal remains, specifically focusing on the tibia and ribs. Protein identification was performed using two strategies: a tryptic-specific search and a semitryptic search, the latter being particularly beneficial in cases of natural protein degradation. The Random Forest algorithm was used to model protein abundance data, enabling the prediction of PMI. A thorough screening process, combining importance scores and SHAP values, was employed to identify the most informative proteins for model’s training and accuracy.ResultsA minimal set of three biomarkers—K1C13, PGS1, and CO3A1—was identified, significantly improving the prediction accuracy between PMIs of 15 and 20 years. The model, based on protein abundance data from semitryptic peptides in tibia samples, achieved sustained 100% accuracy across 100 iterations. In contrast, non-supervised methods like PCA and MCA did not yield comparable results. Additionally, the use of semitryptic peptides outperformed tryptic peptides, particularly in tibia proteomes, suggesting their potential reliability in late PMI prediction.ConclusionsDespite limitations such as sample size and PMI range, this study demonstrates the feasibility of combining proteomics and machine learning for accurate late PMI predictions. Future research should focus on broader PMI ranges and various bone types to further refine and standardize forensic proteomic methodologies for PMI estimation.

Post-mortem Interval estimate based on dental pulp: A histomorphology approach.

Estimating the post-mortem interval (PMI) of human remains based on the histomorphology of dental pulp parameters is promising, but available evidence is scarce and sometimes contradictory without a scientific model. The aim of the study is to characterise the histomorphological changes of dental pulp associated with the decomposition of human remains by a qualitative and quantitative approach. The main aim is to establish a correlation based on post-mortem (PM) dental pulp histomorphology and the PMI, and whether pulp degradation could be an available medico-legal tool for PMI estimation beyond the first week after death (late PMI). The eligible sample consisted of 27 sound teeth from 16 healthy patients aged 16 to 72 years due to orthodontic or oral surgery treatment, to create PMI's simulating the death of the subject as the time elapsed from tooth avulsion. Data collected from patients (sex, date of birth, tooth position, date and hour of the avulsion, date and hour of pulp extraction) were anonymised in accordance with the requirements of Faculty of Dental Medicine of the University of Lisbon. The sample was divided into 9 groups of 3 teeth according to different PMI sets from T0 (baseline) up to 2 weeks (T0, 7, 12, 24, 36, 48, and 72 hours, 1 and 2 weeks). All the dental samples were stored at room temperature up to the time of pulp extraction and then prepared with haematoxylin and eosin stain. High-resolution microscopy was performed to obtain histological images. An operator performed the qualitative evaluation of blood vessels, collagen fibres, and the extra-cellular matrix (ECM) in PM pulps and measured the variation in cells/nuclei density by counting 6 different ROIs (Regions of Interest) for each pulp manually and automatically (quantitative analysis). Qualitative results showed that the degeneration of dental pulp appears 7 hours after death but histological changes in vessels, fibres, and ECM in PM dental pulp are characterised by high variability, consequently it is not possible to generalise the results for early PMIs. Quantitative measurements proved that cell count cannot be standardised due to the presence of superimposed layers of cells and nuclei fragmentation. Odontoblasts did not demonstrate evidence of cellular or nuclear lysis up to 14 PM suggesting their applicability in late PMIs. Future research will focus on late PMIs and different techniques of tooth preparation.

Dental DNA Mutations Occurring after Death: A Novel Method for Post-Mortem Interval (PMI) Estimation.

Post-mortem interval (PMI) estimation remains one of the major challenges in forensic practice, especially for late PMIs beyond 7-10 days after the death of the subject. In 2022, an innovative method to investigate the occurrence of mutations induced by the death of a subject in the DNA of post-mortem dental pulps at different PMIs was developed, applying a next-generation sequencing (NGS) analysis. The present study aims to apply the same method of analysis to a small sample of teeth belonging to the same subject and analyzed at different PMIs/accumulated degree days (ADDs), and of teeth extracted from different subjects but analyzed at the same PMI/ADD to verify the repeatability of the results obtained in relation to the time elapsed since death. A total of 10 teeth were collected from 6 patients (3 males and 3 females) with PMI varying from 8 to 35 days, and ADD from 157.4 to 753.8. We found 1754 mutations in 56 genes, with more than 700 mutations having a prevalence > 5% and more than 300 variants considered of interest for the purposes of the study. Mutations that were not present at lower PMIs but manifested in later PMIs in pulps belonging to the same subject demonstrate that they can only have been acquired by the subject after death and according to the time elapsed since death. In total, 67 somatic mutations in 29 out of the 56 genes of the used panel occurred in a fashion that allows an association with specific PMI/ADD ranges (within 8 days, between 17 and 28, and beyond 30 days after death). The results suggest that temperature and humidity could influence the rate of DNA degeneration in dental pulps, thus PMI should be estimated in ADD more than days. The preliminary validation supports the hypothesis that the innovative method could be a useful tool for estimating the post-mortem interval even beyond the first week after death, but further analyses are needed to customize a specific genetic panel for forensic investigations and verify the influence of degenerative processes of soft tissues surrounding dental elements on DNA degeneration of pulps.

Proteomic Characterization of Changes in Mouse Brain Cortex Protein Expression at Different Post-Mortem Intervals: A Preliminary Study for Forensic Biomarker Identification.

Accuracy in the evaluation of death-induced tissue degradation for thanato-chronological purposes is strictly dependent on the condition of the biological source as well as on the precision of post-mortem interval (PMI) estimation. Thus, the optimization of tissue handling and identification of sensitive post-mortem biomarkers could help establish a timeline for post-mortem events. To this aim, we investigated the proteome changes in cortex samples of 6-week-old female SAMR1 mice over a post-mortem time course. After death, brain tissue was removed immediately (T0), and after 4, 8, 12, 24, and 32 h, four mice were used for each time period, and animals were maintained at 4 °C until brain removal. Dissected tissues were frozen at -80 °C until processed. Proteomic analysis, performed on samples related to early and late PMIs (<24 h and >24 h post-mortem, respectively) showed protein level changes as compared to T0 samples, with a remarkable increase in Calpain11 in the early PMI, as well as in Caspases 7 and 8 together with Gasdermin 3 in late PMI. These findings were confirmed by LIFT mass spectrometry technology and western blot analysis and, although requiring further investigation in other biological samples, suggest that these proteins could be considered as putative biomarkers of different PMIs.

Estimation of Post-mortem Interval Based on Livor Mortis using a Colorimeter in Thai Populations

OBJECTIVE Livor mortis is a helpful and widely used method of estimating postmortem interval (PMI) in Thailand. This study aimed to investigate the value of a colorimeter as a tool for estimating the PMI. METHODS The color of livor mortis and control skin in 80 cadavers whose PMI was within 12 hours was measured by a colorimeter. The L* (brightness), a*b* (chroma and hue), and ∆E* values were compared to the control skin values. Statistical analysis was performed to determine the relationship between PMI and skin color before and after application of a specific pressure. RESULTS The results showed that colorimetric parameters were only weakly correlated with the PMI. An univariable analysis of ∆E* values was performed and showed good discriminatory power, with an area under the ROC curve of 0.82. The recommended cut-off value of ∆E* was 14 for the discrimination between early PMI (less than 6 hours) and late PMI (6-12 hours), in which the sensitivity and specificity were 72.5% and 80%. CONCLUSIONS The findings in this study reinforce the utility of colorimetric measurements in PMI estimation. With additional study and a larger sample size, the estimation of PMI could be established for general use in forensic practice.

Post-mortem CT radiomics for the prediction of time since death.

Post-mortem interval (PMI) estimation has long been relying on sequential post-mortem changes on the body as a function of extrinsic, intrinsic, and environmental factors. Such factors are difficult to account for in complicated death scenes; thus, PMI estimation can be compromised. Herein, we aimed to evaluate the use of post-mortem CT (PMCT) radiomics for the differentiation between early and late PMI. Consecutive whole-body PMCT examinations performed between 2016 and 2021 were retrospectively included (n = 120), excluding corpses without an accurately reported PMI (n = 23). Radiomics data were extracted from liver and pancreas tissue and randomly split into training and validation sets (70:30%). Following data preprocessing, significant features were selected (Boruta selection) and three XGBoost classifiers were built (liver, pancreas, combined) to differentiate between early (< 12h) and late (> 12h) PMI. Classifier performance was assessed with receiver operating characteristics (ROC) curves and areas under the curves (AUC), which were compared by bootstrapping. A total of 97 PMCTs were included, representing individuals (23 females and 74 males) with a mean age of 47.1 ± 23.38years. The combined model achieved the highest AUC reaching 75% (95%CI 58.4-91.6%) (p = 0.03 compared to liver and p = 0.18 compared to pancreas). The liver-based and pancreas-based XGBoost models achieved AUCs of 53.6% (95%CI 34.8-72.3%) and 64.3% (95%CI 46.7-81.9%) respectively (p > 0.05 for the comparison between liver- and pancreas-based models). The use of radiomics analysis on PMCT examinations differentiated early from late PMI, unveiling a novel image-based method with important repercussions in forensic casework. This paper introduces the employment of radiomics in forensic diagnosis by presenting an effective automated alternative method of estimating post-mortem interval from targeted tissues, thus paving the way for improvement in speed and quality of forensic investigations. • A combined liver-pancreas radiomics model differentiated early from late post-mortem intervals (using a 12-h threshold) with an area under the curve of 75% (95%CI 58.4-91.6%). • XGBoost models based on liver-only or pancreas-only radiomics demonstrated inferior performance to the combined model in predicting the post-mortem interval.

Estimation of Late Postmortem Interval: Where Do We Stand? A Literature Review.

Estimating time since death can be challenging for forensic experts, and is one of the most challenging activities concerning the forensic world. Various methods have been assessed to calculate the postmortem interval on dead bodies in different stages of decomposition and are currently widely used. Nowadays, the only well-recognized dating technique is carbon-14 radioisotope measurement, whereas other methods have been tested throughout the years involving different disciplines with different and sometimes not univocal results. Today, there is no precise and secure method to precisely determine time since death, and late postmortem interval estimation remains one of the most debated topics in forensic pathology. Many proposed methods have shown promising results, and it is desirable that with further studies some of them might become acknowledged techniques to resolve such a difficult and important challenge. The present review aims at presenting studies about the different techniques that have been tested in order to find a valuable method for estimating time since death for skeletal remains. By providing a comprehensive overview, the purpose of this work is to offer readers new perspectives on postmortem interval estimation and to improve current practice in the management of skeletal remains and decomposed bodies.

Partners in Postmortem Interval Estimation: X-ray Diffraction and Fourier Transform Spectroscopy.

The postmortem interval (PMI) is difficult to estimate in later stages of decomposition. There is therefore a need to develop reliable methodologies to estimate late PMI. This study aims to assess whether there is a correlation between changes in the mineral composition of human teeth and the estimation of PMI. X-ray diffraction (XRD) and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy techniques were performed to address this challenge. Forty healthy human teeth obtained from odontological clinics were stored at different times (0, 10, 25, 50 years; N = 10/group). XRD and ATR-FTIR parameters related to the structure and composition of teeth were studied. Our results showed that the crystallinity index, crystal size index, mineral-to-organic matrix ratio (M/M) and carbonate/phosphate ratio (C/P) had the strongest association with PMI. For larger PMIs, there was a significant increase in crystallinity, crystal size and M/M ratio, while the C/P ratio showed a specific decrease with increasing PMI. According to our results, the parameters of crystallinity, crystal size, M/M ratio and C/P ratio can be considered highly accurate in determining a PMI of 10 years of data; crystallinity and mineral maturity can be considered useful in determining a PMI of 25 years; and crystallinity and mineral maturity can be considered highly accurate in determining a PMI of 50 years. A particular XRD index was identified as the most suitable parameter to estimate PMI: crystallinity. The joint use of XRD and ATR-FTIR analyses could be a promising alternative for dating human teeth.

Systematic Review on Post-Mortem Protein Alterations: Analysis of Experimental Models and Evaluation of Potential Biomarkers of Time of Death.

Estimating the post-mortem interval (PMI) is a very complex issue due to numerous variables that may affect the calculation. Several authors have investigated the quantitative and qualitative variations of protein expression on post-mortem biological samples in certain time intervals, both in animals and in humans. However, the literature data are very numerous and often inhomogeneous, with different models, tissues and proteins evaluated, such that the practical application of these methods is limited to date. The aim of this paper was to offer an organic view of the state of the art about post-mortem protein alterations for the calculation of PMI through the analysis of the various experimental models proposed. The purpose was to investigate the validity of some proteins as “molecular clocks” candidates, focusing on the evidence obtained in the early, intermediate and late post-mortem interval. This study demonstrates how the study of post-mortem protein alterations may be useful for estimating the PMI, although there are still technical limits, especially in the experimental models performed on humans. We suggest a protocol to homogenize the study of future experimental models, with a view to the next concrete application of these methods also at the crime scene.

Physicochemical Changes in Bone Bioapatite During the Late Postmortem Interval Pre- and Post-Burning.

Postmortem chemical transformation of bone bioapatite can take place during early diagenesis, resulting in a more thermodynamically stable mineral phase. This paper examines the impact of a one year postmortem interval on unburnt and burnt bone’s structural and chemical alterations. This question is of importance for the reconstruction of funerary practices involving cremation in the archaeological record, as well as forensic anthropological investigations. Fleshed pig (Sus scrofa) tibiae were left exposed in a field, then collected at 14, 34, 91, 180, and 365 day intervals prior to being burnt in an outdoor fire (≤750 °C bone temperature). Fresh (fleshed) tibiae acted as unburnt and burnt controls. Also included in the study were two cremated human bone fragments from Middle–Late Neolithic (ca. 3300–2500 BCE) Ireland. Samples were analyzed for major and trace elements using an electron microprobe wavelength dispersive analyzer and molecular structures using Fourier transform infrared spectroscopy. Linear regression, principal component analysis, linear discriminant analysis, and multivariate analysis of variance were performed for statistical analysis. Results indicate that the concentrations of elements associated with extracellular fluid (K, Na, and Cl) change with the postmortem interval (PMI) and survive burning. K values under 0.07 ± 0.01 wt% in the inner and mid-cortical zones of burnt bones suggest that bones were not burnt immediately after death. Using this criterion, results from the archaeological samples would indicate a PMI of at least weeks to months prior to cremation. Ca, P, Fe, Al, Si, and Sr are not significantly altered with burning, and Fe, Al, Si, and Sr are also unaffected by the PMI. In unburnt bones increased crystallinity and carbonate loss are detectable in <1 year, but both are obscured by burning. Structurally, the carbonate to phosphate ratio (C/P), the phosphate high temperature, and cyanamide to phosphate (CN/P) are the most useful ratios for discriminating between unburnt and burnt bones.

High-throughput sequencing to evaluate the effects of methamphetamine on the succession of the bacterial community to estimate the postmortem interval

In forensic medical examinations, estimating the postmortem interval (PMI) is an important factor. Methamphetamine (MA) is a synthetic stimulant that is commonly abused, and estimation of the PMI after MA abuse has become one of the main tasks in forensic investigation. Microorganisms play a vital role in carrion decomposition. Analysing the bacterial succession patterns can be used as a forensic tool to estimate the PMI. The present study aimed to analyse bacterial succession changes during the decomposition of MA to estimate the PMI. We analysed bacterial communities in rabbits treated with three different concentrations of MA (0, 22.5, and 90 mg/kg) under the natural conditions of 20 °C and 70% humidity by sequencing 16S rRNA gene amplicons using the Illumina MiSeq system. We obtained 2 774 209 high-quality sequences and 2937 operational taxonomic units (OTUs). The relative abundances of the bacterial communities varied markedly in response to different MA concentrations. Interestingly, in response to the different concentrations of MA, Bacteroidetes became disparate in the rectum in the late PMI. Increased numbers of bacterial taxa were identified in the rectum and buccal cavity samples, except at the highest concentration of MA in the rectum samples when PMI was 0–h, than were present in live rabbits. Meanwhile, the PMI correlated significantly with bacterial succession at different taxonomic levels. Our results suggested that bacterial community succession could be used as a “microbial clock” to estimate the PMI in cases of MA-related death; however, further study is required to gain a deeper understanding of this concept. Keypoints As a forensic tool, microbiome succession patterns have great potential for PMI estimation. At different taxonomic levels, the variation in the succession of microorganisms’ under three different concentrations of MA during the processes of decomposition is significantly related to PMI for estimating MA abuse. These findings provide a new idea for the estimation of PMI of MA abused by changes in microorganisms.

AURICULAR CARTILAGE AS A TOOL FOR POSTMORTEM INTERVAL ESTIMATION IN HUMAN

Background: An accurate estimation of the postmortem (PM) interval, despite of being a routine daily forensic expert work, is still a challenging practice. Science continues growing in this topic. Cartilage is a specific avascular, non-lymphatic, and non-nervous specific connective tissue. Objectives: This work aimed to assess the use of auricular elastic cartilage as a tool for estimation of late PM interval in human. Methods: Biopsies were taken from ear cartilages of 43 victims how died from suspicious criminal causes. Routine haematoxylin and eosin (H&E) was performed. The following histopathological parameters were examined, perichondrium, the number of lacunae with chondrocytes, nuclear material, and extracellular matrix. Scoring system was used for each parameter in different postmortem (PM) interval. Results: Cases were classified to 3 groups (1-7, 8-14, and 15-21 days PM). The examined 4 histological parameters give statistically significant changes across the tested PM interval. Correlation coefficient between the 4 parameters and PM interval give significant results. The r value was highest with percentage of lacunae without chondrocytes and lowest with perichondrium loss (r = 0.62 and 0.35 respectively). Conclusion: Auricular cartilage showed remarkable changes that are correlated with PM interval in human. In the future, large sample should be used with studying the impaction of environmental factors on these changes.

Estimation of the time of death: where we are now?

One of the increasingly discussed topics in forensic pathology is that concerning the quantification of the postmortem interval (PMI). The estimation of the time interval between the death of a person and the discovery of the body is extremely complicated, as it is affected by the influence of many factors, both endogenous and exogenous. With the advancement of knowledge in the field of molecular biology, several studies have been performed, for more than 30 years, on the degradation pattern of macromolecules, such as proteins, DNA, RNA, and the relationship with PMI. Despite initial enthusiasm, studies have shown different kind of limitations in determining PMI in the forensic field. In the last years, consequently, researchers focused their attention on the potential of microRNAs as housekeeping genes, due to their postmortem stability and resistance to degradation. MiRNAs are small, endogenous, single stranded, non-coding RNA molecules identified in plants, animals and DNA virus transcriptome. Various and growing are the fields of application: to establish time of death, to evaluate vitality of skin lesions, in cases of head trauma, and cases of acute myocardial infarction. Their use could also be particularly useful in determining late PMI (beyond 24 hours after death), as no additional markers are available in this scenario. At the moment, scientific research is still at an early stage as it is mainly based on animal models. However, the promising properties of miRNAs and their low cost may make this field of research very interesting for an increasingly precise determination of PMI in the future.

A field study to evaluate PMI estimation methods for advanced decomposition stages

Estimating the postmortem interval (PMI) is one of the major tasks and a continuous challenge in forensic pathology. It is often an exclusion process of available methods, which ultimately can lead to an unsatisfactory outcome due to poor reliability. This problem is most acute in the late PMI, when decomposition proceeds and some methods (such as rigor, livor, and algor mortis) are no longer applicable. Several methods, such as forensic entomology, skeletal muscle protein degradation, and the study of body decomposition by application of a morphological scoring, are expected to provide further information; however, all have certain limitations and weaknesses. Availability of a tool-box of methods allows a case-specific selection of the most appropriate one(s), or eventually provides improvements in the overall accuracy and precision of the PMI estimation by merging and combining methods. To investigate practical (field) application, eventual interferences, and/or synergetic effects, as well as the robustness of these methods towards specific influencing factors, a field study was conducted, using eight pig cadavers of different body weights and physical coverage, left to decompose under natural conditions for 16 days. Morphological changes during decomposition were assessed using the total body score (TBS), muscle samples were collected to analyze protein degradation, and insect colonization was evaluated. The results reveal strengths and current limitations of all tested methods, as well as promising synergistic effects, and thus, provide a baseline for targeted future research.

Succession of oral microbiota community as a tool to estimate postmortem interval

The establishment of postmortem interval is one of the most important aspects of forensic expertise. Microbes may provide a novel way to estimate the postmortem intervals in order to avoid many of these limitations. The oral cavity harbors one of the most diverse microbiomes that play a key role in the decomposition of corpses. In this study, the oral bacterial community showed obvious changes in relative abundance during the process of mice decomposition. Meanwhile, at different taxonomic levels, specific bacteria were found to be significantly correlated with the postmortem interval. Linear regression models between relative abundance and the postmortem interval were constructed. Among these species, Gamma-proteobacteria and Proteus were the best ones that can be used to infer the postmortem interval, especially late postmortem interval. Therefore, we suggest that succession of oral microbial community can be developed as a forensic tool for estimating the postmortem interval.

Trimethylamine in postmortem tissues as a predictor of postmortem interval estimation using the GC method.

Trimethylamine (TMA), a simple amine in volatile compounds, indicating the spoilage degree of meat, related with the late postmortem interval (PMI) during the cadaver decomposition process. In this paper, a headspace gas chromatography (HS-GC) method has been successfully built to analyze the content of TMA in postmortem rat tissues (liver, myocardial and skeletal muscle tissues), which is used for PMI estimation with the wide range of PMI (0-720 h postmortem) at 16 °C ± 1 °C. Correspondingly, three equations about the relationship between the PMI and TMA content were established, in which they showed that the TMA content in all three tissues increased from the firstly detected time to 192 h and gradually decreased after 384 h. Furthermore, the TMA measurement in five human samples was carried out and the results (<35 h PMI) showed a good agreement about the change trend of TMA content between human and rat, which elucidated that this research might provide a new insight for the forensic scientist to band HS-GC technology together with TMA determination in the PMI estimation.

Antemortem, Perimortem And Postmortem Bone Fracture: Could Histopathology Differentiate Between them?

One of the important duties of the forensic experts is to differentiate between antemortem, perimortem, and postmortem bone fracture to estimate the postmortem interval. This study aimed to differentiate between antemortem, perimortem and postmortem bone fracture in late postmortem interval by histopathological technique. Sixty rats were equally divided into 6 groups. The first, second, third, and fourth groups involved rats that their left femora were fractured and left alive for 6, 3, 1 days and 12 hr. before scarification respectively. The fifth and sixth groups included rats that their left femora were fractured just before death and 2 hours postmortem respectively. Bone fracture was examined 3 and 6 days postmortem. Bone samples were stained with hematoxylin and eosin stain (H&E), trichrome stain, and Prussian blue (iron stain). Hemorrhage, the number of osteocyte nuclei, the number of bone marrow nuclei, and the degree of bone marrow dehydration were assessed. Our results revealed that hemorrhage was more evidenced in 1-day fracture, then 3 days and 12 hours, while, less in 6 days and at time of death. It was absent in postmortem fracture. There were significant decreases in the number of osteocytes and bone marrow nuclei, bone marrow hydration, and Prussian blue when examined at 6 days postmortem in comparing with 3 days postmortem. This study concluded that H&E and trichrome stain succeeded in estimation of the age of the long bone fracture and differentiation between antemortem, perimortem and postmortem fracture, while Prussian blue stain showed insignificant changes in fracture produced just before death.

Relationship between Electrical Conductivity and Decomposition Rate of Rat Postmortem Skeletal Muscle

To analyze the relationship among electrical conductivity （EC）, total volatile basic nitrogen （TVB-N）, which is an index of decomposition rate for meat production, and postmortem interval （PMI）. To explore the feasibility of EC as an index of cadaveric skeletal muscle decomposition rate and lay the foundation for PMI estimation. Healthy Sprague-Dawley rats were sacrificed by cervical vertebrae dislocation and kept at 28 ℃. Muscle of rear limbs was removed at different PMI, homogenized in deionized water and then skeletal extraction liquid of mass concentration 0.1 g/mL was prepared. EC and TVB-N of extraction liquid were separately determined. The correlation between EC (x₁) and TVB-N (x₂) was analyzed, and their regression function was established. The relationship between PMI (y) and these two parameters were studied, and their regression functions were separately established. The change trends of EC and TVB-N of skeletal extraction liquid at different PMI were almost the same, and there was a linear positive correlation between them. The regression equation was x₂=0.14x₁-164.91(R²=0.982). EC and TVB-N of skeletal muscle changed significantly with PMI, and the regression functions were y=19.38x₁³-370.68x₁²+2 526.03 x₁-717.06(R²=0.994), and y=2.56x₂³-48.39x₂²+330.60x₂-255.04(R²=0.997), respectively. EC and TVB-N of rat postmortem skeletal muscle show similar change trends, which can be used as an index for decomposition rate of cadaveric skeletal muscle and provide a method for further study of late PMI estimation.

Determining the electrical conductivity of rat cadaveric liver, spleen, and kidney to estimate early postmortem interval

Previous research has found that electrical conductivity (EC), an important index to predict meat freshness and shelf life, is very promising for estimating the late postmortem interval (PMI). However, whether it has potential use in the early PMI has not been fully studied yet. To test this possibility in the present study, EC of three internal organs of rat liver, spleen, and kidney were determined within 24 postmortem hours, and then, EC changes at different PMIs were carefully analyzed. The overall results showed that EC of liver and spleen increased significantly with PMI while EC of kidney had minor changes during the same period. Specifically, significant linear positive correlations between EC of liver and spleen and PMI were found and the coefficients of their regression functions were R2 = 0.98 and R2 = 0.95, respectively. It can be concluded that determination of EC in certain internal organs such as liver and spleen may be a potential tool in the early PMI estimation. However, more researches on its influencing factors are needed to facilitate its final use in practice.

Characterization of postmortem biochemical changes in rabbit plasma using ATR-FTIR combined with chemometrics: A preliminary study

Postmortem interval (PMI) determination is one of the most challenging tasks in forensic medicine due to a lack of accurate and reliable methods. It is especially difficult for late PMI determination. Although many attempts with various types of body fluids based on chemical methods have been made to solve this problem, few investigations are focused on blood samples. In this study, we employed an attenuated total reflection (ATR)-Fourier transform infrared (FTIR) technique coupled with principle component analysis (PCA) to monitor biochemical changes in rabbit plasma with increasing PMI. Partial least square (PLS) model was used based on the spectral data for PMI prediction in an independent sample set. Our results revealed that postmortem chemical changes in compositions of the plasma were time-dependent, and various components including proteins, lipids and nucleic acids contributed to the discrimination of the samples at different time points. A satisfactory prediction within 48h postmortem was performed by the combined PLS model with a good fitting between actual and predicted PMI of 0.984 and with an error of ±1.92h. In consideration of the simplicity and portability of ATR-FTIR, our preliminary study provides an experimental and theoretical basis for application of this technique in forensic practice.