Temperature based forensic death time estimation: The standard model in experimental test

geoFOR: A collaborative forensic taphonomy database for estimating the postmortem interval

Accurately assessing the postmortem interval (PMI), or the time since death, remains elusive within forensic science research and application. This paper introduces geoFOR, a web-based collaborative application that utilizes ArcGIS and machine learning to deliver improved PMI predictions. The geoFOR application provides a standardized, collaborative forensic taphonomy database that gives practitioners a readily available tool to enter case information that automates the collection of environmental data and delivers a PMI prediction using statistically robust methods. After case submission, the cross-validating machine learning PMI predictive model results in a R² value of 0.82. Contributors receive a predicted PMI with an 80% confidence interval. The geoFOR database currently contains 2529 entries from across the U.S. and includes cases from medicolegal investigations and longitudinal studies from human decomposition facilities. We present the overall findings of the data collected so far and compare results from medicolegal cases and longitudinal studies to highlight previously poorly understood limitations involved in the difficult task of PMI estimation. This novel approach for building a reference dataset of human decomposition is forensically and geographically representative of the realities in which human remains are discovered which allows for continual improvement of PMI estimations as more data is captured. It is our goal that the geoFOR data repository follow the principles of Open Science and be made available to forensic researchers to test, refine, and improve PMI models. Mass collaboration and data sharing can ultimately address enduring issues associated with accurately estimating the PMI within medicolegal death investigations.

Nomogram based Postmortem-interval estimation compared with the Actual death-interval in Tropical environmental conditions

BACKGROUND

Estimating an accurate postmortem interval (PMI) is essential for death investigators to confirm the offence timing and suspects' alibis. Compared to traditional methods, the Nomogram-based method is claimed to estimate nearly accurate PMI, but most of such studies are based on the Western population. Adequate data for bodies exposed to tropical climate of India and the Indian subcontinent are not available.

AIM

To assess the accuracy and goodness-of-fit of Nomogram based PMI estimation in bodies exposed to Indian climatic conditions after death.

MATERIAL AND METHODS

This is a 3-year-long study on 200 bodies with known death times. The exact PMI was recorded from direct sources: family members, police and hospital records. Before autopsy, the ambient temperature, body weight, length, and rectal temperature were measured, and the details of clothing, sex, and age, were used on a nomogram to calculate the PMI (tN). One-way ANOVA correlation and Mann-Whitney U test were used to compare the variables. Linear regression analysis was used to establish the relationship between the rectal temperature (Tr) and nomogram estimated PMI (tN) and the known PMI(t). The consistency and agreement between the tN and t were measured using Intra-class correlation coefficient (ICC). Bland-Altman (BA) plot was used to compare the level of agreement between direct(t) and nomograms method PMIs.

RESULTS

Nomogram-based PMI estimation showed a statistically significant strong relationship with rectal temperature (R 0.77, R2 0.74, adjusted R2 0.76, t-stat 25.83 p < 0.000) and exhibited a relatively consistent agreement with the known death interval (ICC 0.935). Regressing the tN over t showed that the nomogram method can predict PMI with 95 % accuracy. The BA plot between Direct and Nomogram methods exhibited a consistent agreement in PMI estimation though the limits of agreement (LoA) were wide: range 39.09-121.18 min.

CONCLUSION

The accuracy and reliability of the Nomogram method in PMI estimation is high and recommended for the South Indian population. However, the presence of systematic differences between tN and t can't be ruled out due to wider LoA in BA plot. Hence, these findings highlight the need for further investigation and potential refinement of the PMI estimation methods to enhance accuracy and reduce discrepancies.

[Cardiac implantable electric devices in forensic medicine : Overview from the forensic and cardiology perspective]

In 2021, about 75,000 persons in Germany died unnaturally or due to unexplained reasons. As a consequence, there are difficulties in more precisely identifying the time, cause and circumstances of death. Nevertheless, clarification is crucial not only from the clinical perspective, but these data are of considerable importance in the context of investigative procedures as they can be used to answer numerous legally relevant questions. Cardiac implantable devices (CIED) are of vital importance in the treatment of cardiac arrhythmias. In 2020 about 100,000 patients underwent CIED implantation in Germany. Therefore, CIED are present in a relevant proportion of the deceased mentioned above. The valuable source of information represented by postmortal CIED interrogation has been shown in numerous studies. Nevertheless, postmortal CIED interrogation is not routinely performed in the context of forensic medical examinations for reasons of practicability. This article summarizes benefits and limitations of postmortal CIED interrogation from the perspective of forensic medicine and cardiology and gives a recommendation for realization.

Next-generation time of death estimation: combining surrogate model-based parameter optimization and numerical thermodynamics

The postmortem interval (PMI), i.e. the time since death, plays a key role in forensic investigations, as it aids in the reconstruction of the timeline of events. Currently, the standard method for PMI estimation empirically correlates rectal temperatures and PMIs, frequently necessitating subjective correction factors. To address this shortcoming, numerical thermodynamic algorithms have recently been developed, providing rigorous methods to simulate postmortem body temperatures. Comparing these with measured body temperatures then allows non-subjective PMI determination. This approach, however, hinges on knowledge of two thermodynamic input parameters, which are often irretrievable in forensic practice: the ambient temperature prior to discovery of the body and the body temperature at the time of death (perimortem). Here, we overcome this critical limitation by combining numerical thermodynamic modelling with surrogate model-based parameter optimization. This hybrid computational framework predicts the two unknown parameters directly from the measured postmortem body temperatures. Moreover, by substantially reducing computation times (compared with conventional optimization algorithms), this powerful approach is uniquely suited for use directly at the crime scene. Crucially, we validated this method on deceased human bodies and achieved the lowest PMI estimation errors to date (0.18 h ± 0.77 h). Together, these aspects fundamentally expand the applicability of numerical thermodynamic PMI estimation.

Postmortem Electrical Conductivity Changes of Dicentrarchus labrax Skeletal Muscle: Root Mean Square (RMS) Parameter in Estimating Time since Death

Simple Summary

The estimation of postmortem interval (PMI) still poses a major challenge for pathologists worldwide, making the search for new and more accurate technologies to assist in PMI estimation worthy of growing scientific interest. This study aimed to explore for the first time the use of an oscilloscope coupled with a signal generator, as innovative technology, to evaluate changes in the electrical conductivity of skeletal muscle of sea bass specimens during the early postmortem interval, to find an accurate, quantitative parameter useful in PMI estimation. The use of the oscilloscope, especially for the RMS measured parameter, has been shown here as a promising technology for studying dielectric muscle properties during the early postmortem interval, with the advantage of being a rapid, non-destructive, and inexpensive method.

Abstract

Electric impedance spectroscopy techniques have been widely employed to study basic biological processes, and recently explored to estimate postmortem interval (PMI). However, the most-relevant parameter to approximate PMI has not been recognized so far. This study investigated electrical conductivity changes in muscle of 18 sea bass specimens, maintained at different room temperatures (15.0 °C; 20.0 °C; 25.0 °C), during a 24 h postmortem period using an oscilloscope coupled with a signal generator, as innovative technology. The root mean square (RMS) was selected among all measured parameters, and recorded every 15 min for 24 h after death. The RMS(t) time series for each animal were collected and statistically analyzed using MATLAB^®. A similar trend in RMS values was observed in all animals over the 24 h study period. After a short period, during which the RMS signal decreased, an increasing trend of the signal was recorded for all fish until it reached a peak. Subsequently, the RMS value gradually decreased over time. A strong linear correlation was observed among the time series, confirming that the above time-behaviour holds for all animals. The time at which maximum value is reached strongly depended on the room temperature during the experiments, ranging from 6 h in fish kept at 25.0 °C to 14 h in animals kept at 15.0 °C. The use of the oscilloscope has proven to be a promising technology in the study of electrical muscle properties during the early postmortem interval, with the advantage of being a fast, non-destructive, and inexpensive method, although more studies will be needed to validate this technology before moving to real-time field investigations.

Individualised and non-contact post-mortem interval determination of human bodies using visible and thermal 3D imaging

Determining the time since death, i.e., post-mortem interval (PMI), often plays a key role in forensic investigations. The current standard PMI-estimation method empirically correlates rectal temperatures and PMIs, frequently necessitating subjective correction factors. To overcome this, we previously developed a thermodynamic finite-difference (TFD) algorithm, providing a rigorous method to simulate post-mortem temperatures of bodies assuming a straight posture. However, in forensic practice, bodies are often found in non-straight postures, potentially limiting applicability of this algorithm in these cases. Here, we develop an individualised approach, enabling PMI reconstruction for bodies in arbitrary postures, by combining photogrammetry and TFD modelling. Utilising thermal photogrammetry, this approach also represents the first non-contact method for PMI reconstruction. The performed lab and crime scene validations reveal PMI reconstruction accuracies of 0.26 h ± 1.38 h for true PMIs between 2 h and 35 h and total procedural durations of ~15 min. Together, these findings broaden the potential applicability of TFD-based PMI reconstruction.

Establishing the time since death (TSD) is vital in many forensic investigations. By combining thermometry, photogrammetry and numerical thermodynamic modelling, the TSD can be determined non-invasively for bodies of arbitrary shape and posture with an unprecedented accuracy of 0.26 h ± 1.38 h.

The time of death in Dutch court; using the Daubert criteria to evaluate methods to estimate the PMI used in court

When a capital crime is committed the post-mortem interval (PMI) is of particular importance in investigating a suspect's alibi in court. A forensic expert can use different methods to estimate the PMI. This research focuses on who is considered an expert in court and whether the methods used to estimate the PMI are reliable. In this study, the methods used to estimate the PMI and the experts consulted, available in Dutch jurisprudence, in the period 2010-2019 were investigated. Ninety-four judicial cases were included and multiple experts and methods of estimating the PMI were found. As part of this study, the methods that were used to estimate the PMI in court were subjected to the Daubert criteria. Of these methods, only the Henssge nomogram and entomological methods met the Daubert criteria. However, the methods are only useful when applied by the right forensic expert and in the right manner. Unfortunately, this was not always the case.

Simultaneous analysis of potassium and ammonium ions in the vitreous humour by capillary electrophoresis and their integrated use to infer the post mortem interval (PMI)

Post-mortem changes of ions in the body fluids have been proposed as an objective tool for inferring the time of death. In particular, the post-mortem increase of potassium concentrations in the vitreous humour has gained great attention in the literature. On the other hand, ammonium, another ion released in post-mortem processes, has received much less attention, potentially due to unresolved analytical issues using current clinical chemistry methods. This paper presents an application of a new analytical approach based on capillary electrophoresis providing the simultaneous analysis of potassium and ammonium ions in the vitreous humour. In addition, to assess the consistency of the post-mortem increase of ammonium concentrations in the vitreous humour, the determination of this ion in the vitreous humour of the two eyes of the same body at the same post-mortem interval has been verified. Vitreous humour was collected from 33 medico-legal cases where the time of death was known exactly. Prior to analysis, all samples were diluted 1:20 with a 40 μg/mL solution of BaCl₂ (internal standard). In the study of the variability of the ammonium concentration between the two eyes, no statistically significant differences were found, supporting the hypothesis of an even post-mortem increase of the ion concentrations in this particular biological fluid. Significant correlations of potassium and ammonium ions with the post-mortem interval were found, with r² of 0.75 and 0.70, respectively.

Uncertainty in the estimation of the postmortem interval based on rectal temperature measurements: A Bayesian approach

In this work, the postmortem interval is estimated by means of Bayesian inference using rectal temperature data from a published database. First, a systematic analysis of the uncertainties in each of the model parameters is carried out in order to assess their relative influences on the postmortem interval uncertainty. Then, the method is applied to the whole database and proves to be more reliable than the well-established nomogram method. Moreover, the result of the Bayesian inference process is the full posterior probability distribution of the postmortem interval, which provides more information than a simple point estimate or a time interval. This distribution can be used to assign probabilities to specific time intervals that may arise in a criminal investigation. The application of this statistical analysis can be extended to any method of estimating the postmortem interval.

Feasibility Study of MRI Muscles Molecular Imaging in Evaluation of Early Post-Mortem Interval

Estimating early postmortem interval (EPI) is a difficult task in daily forensic activity due to limitations of accurate and reliable methods. The aim of the present work is to describe a novel approach in the estimation of EPI based on quantitative magnetic resonance molecular imaging (qMRMI) using a pig phantom since post-mortem degradation of pig meat is similar to that of human muscles. On a pig phantom maintained at 20° degree, using a 1.5 T MRI scanner we performed 10 scans (every 4 hours) monitoring apparent diffusion coefficient (ADC), fractional anisotropy (FA) magnetization transfer ration (MTR), tractography and susceptibility weighted changes in muscles until 36 hours after death. Cooling of the phantom during the experiment was recorded. Histology was also obtained. Pearson’s Test was carried out for time correlation between post-mortem interval and MRI data. We found a significative inverse correlation between ADC, FA, MT values and PMI. Our preliminary data shows that post-mortem qMRMI is a potential powerful tool in accurately determining EPI and is worth of further investigation.

Computationally approximated solution for the equation for Henssge's time of death estimation

Background

Time of death estimation in humans for the benefit of forensic medicine has been successfully approached by Henssge, who modelled body cooling based on measurements of Marshall and Hoare. Thereby, body and ambient temperatures are measured at the death scene to estimate a time of death based on a number of assumptions, such as initial body temperature and stable ambient temperature. While so far, practical use of the method resorted to paper print outs or copies of a nomogram using a ruler, increasingly, users are interested in computer or mobile device applications. We developed a computational solution that has been available online as a web accessible PHP program since 2005. From that, we have received numerous requests not so much to detail our code but to explain how to efficiently approximate the solution to the Henssge equation.

Methods

To solve Henssge’s double exponential equation that models physical cooling of a body, it is sufficient to determine a difference term of the equation that will be close to zero for the correct time of death using a discrete set of all sensible possible solutions given that the modelled time frame has practical upper limits. Best post-mortem interval approximation yields minimal difference between equation terms

Results

The solution is approximated by solving the equation term difference for a discrete set of all possible time of death intervals that are sensibly found, and by then determining the particular time of death where equation term difference is minimal.

Conclusions

The advantage of a computational model over the nomogram is that the user is also able to model hypothermia and hyperthermia. While mathematically impossible to solve in a straightforward way, solutions to the Henssge equation can be approximated computationally.

Predictive equation for post-mortem interval using spectrophotometric values of post-mortem lividity: A pilot study

The colour of post-mortem lividity and control skin of 86 cadavers was measured spectrophotometrically to obtain L^* (value), a^* (chroma) and b^* (hue) values. In addition, left heart blood (n = 58), right heart blood (n = 57) and blood from the femoral vein (n = 21) were measured. Using these data, we analysed the relationship between post-mortem lividity, control skin and blood colours. L^* of post-mortem lividity (L^*_p) and control skin (L^*_c) were strongly correlated ( r = 0.64). a^* and b^* of post-mortem lividity (a^*_p and b^*_p) significantly increased with an increasing post-mortem interval (PMI) but r² values were low (0.11 and 0.070, respectively). Predictive equations for post-mortem lividity colour (L^*_p, a^*_p and b^*_p) were developed using control skin colour (L^*_c, a^*_c and b^*_c) and autopsy findings for the first time. The predictive equation for L^*_p explained almost 65% of the observed L^*_p. We created predictive equations for PMI with and without blood colour values, and the most accurate equation, which did not use blood colour values, made it possible to estimate PMI within ± 10.29 h. Further study of these equations will help us to understand the factors that affect post-mortem lividity colour and increase the accuracy of equations for predicting post-mortem lividity colour and PMI.

[Temporal pattern of postmortem color changes in the pupil region of the cornea in rabbits]

OBJECTIVE

To explore the temporal pattern of postmortem color changes in the pupil region of the cornea for noninvasive estimation of the postmortem interval (PMI).

METHODS

Two rabbit models of air embolism and drowning were established in a dark room at a temperature of 20 ℃ with a relative humidity of 30%. The corneal images of the rabbits were acquired using a digital camera at two-hour intervals within 72 h after death. The pupil region on the corneal images was segmented using computer image processing technique (MATLAB), and the parameters of 6 image color features (RGBHSV) were extracted. Regression analysis was used to analyze the relationship between these parameters and the PMI, and the effects of different death causes on the changes of the corneal color features were also assessed.

RESULTS

Within 72 h after death from different causes, the R, G and B values of the pupil region on the corneal images all tended to increase with the PMI, showing a good fitting with the PMI (P &lt; 0.01). No significant correlation was found between the values of H, S and V and the PMI (P&gt;0.05). The R, G and B values in the pupil region on the corneal images showed consistent variation trends after death from the two causes, and their correlations with PMI were also similar. The measured values of R, G and B in air embolism group were greater than those in the drowning group.

CONCLUSIONS

The postmortem color changes of the pupil region on corneal images follow an identifiable temporal pattern and can vary across different causes of death. The regression equations established in this study provide references for non-invasive and objective estimation of the PMI.

A new method for the determination of ammonium in the vitreous humour based on capillary electrophoresis and its preliminary application in thanatochemistry

Background

Although the post-mortem increase of ammonium in biological fluids is well known, ammonium analysis in vitreous humour has never been used in recent times for the determination of the post-mortem interval. The present work represents a new application of capillary electrophoresis with indirect UV detection in the field of forensic analysis.

Methods

The electrophoretic separation was carried out in a running buffer made of 5 mM imidazole, 5 mM 18-crown-6 ether and 6 mM d,l-α-hydroxybutyric acid (HIBA). To overcome the lack of optical absorption of ammonium, indirect UV detection was applied. The used wavelength was 214 nm.

Results

The method showed good linearity in the concentration range from 0.16 to 5.0 mM. The limit of detection, 0.039 mmol/L, was established on the basis of the linearity curve. Precision and bias studies carried out on the pure ammonium solutions and in real biological samples, revealed %RSDs well below 20%. A preliminary application to real cases where the death time was precisely known (14 bodies) was carried out plotting vitreous humour ammonium vs. post-mortem interval with a resulting good linear correlation until 100 h post-mortem.

Conclusions

After validation in real cases, the present method can become a powerful tool to unravel one of the most challenging issues of forensic investigation: determination of the time of death.

Minimum time since death when the body has either reached or closely approximated equilibrium with ambient temperature

In temperature based death time estimation the construction of a death time interval using the conventional Nomogram method (NM) is not permissible for bodies in which rectal temperature (T_r) has reached or closely approximated equilibrium with ambient temperature (T_a). We provide a logic approach to compute a minimum time since death with high probability. We also provide a simple graphical solution to be used at the crime scene for preliminary estimation. Special attention is advised in regards to cases with T_a>23°C as well as borderline cases. Proof by induction, application to test cases and one example of use are presented.

Postmortem Changes in Animal Carcasses and Estimation of the Postmortem Interval

A thorough understanding of the physical and chemical changes that occur in the body after death is critical for accurate interpretation of gross and microscopic pathology at autopsy. Furthermore, knowledge of the postmortem processes and the factors that affect them will aid in the estimation of the postmortem interval (PMI). The estimation of the PMI is important in many human and animal death investigations. Despite many decades of research, accuracy in estimation of the time of death has not significantly improved, and no single method can be reliably used to accurately estimate the time of death. Great care should be taken when formulating such an estimate, for it is dependent on multiple circumstantial and environmental factors, and the accuracy and precision of the estimate decrease as the PMI increases. The majority of the research in the field has been conducted on human bodies, but many relevant conclusions may be drawn regarding the expected postmortem changes in animals and the estimation of the PMI. The veterinary pathologist must use great caution when attempting to extrapolate data and apply formulas designed for use in humans. Methods reviewed include gross changes, microscopic changes, temperature-based methods, postmortem chemistry, molecular methods, microbial assay, ocular changes, radiography, entomology, and others. Although only several of these methods are currently practical for use in the workup of cases, it is expected that future research will result in improved techniques with enhanced accuracy in the estimation of the PMI, which will benefit both human and veterinary forensic investigations.