Holger Muggenthaler

Influence of measurement errors on temperature-based death time determination

Temperature-based methods represent essential tools in forensic death time determination. Empirical double exponential models have gained wide acceptance because they are highly flexible and simple to handle. The most established model commonly used in forensic practice was developed by Henssge. It contains three independent variables: the body mass, the environmental temperature, and the initial body core temperature. The present study investigates the influence of variations in the input data (environmental temperature, initial body core temperature, core temperature, time) on the standard deviation of the model-based estimates of the time since death. Two different approaches were used for calculating the standard deviation: the law of error propagation and the Monte Carlo method. Errors in environmental temperature measurements as well as deviations of the initial rectal temperature were identified as major sources of inaccuracies in model based death time estimation.

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

The determination of the time since death is essential to forensic homicide investigations since the time of death represents the presumed time of the offence. Erroneous death time estimates may lead to false acquittal or conviction of suspects. Since its introduction 30years back, the nomogram method by Henßge has been established as the standard procedure of temperature-based death time determination in the early post-mortem period. The present study provides an independent investigation of the validity of its death time estimates and their corresponding 95%-confidence intervals. Comparison to post-mortem cooling curves recorded under controlled conditions of 84 suddenly deceased with known death times yielded the following results: Since in the light of our experiments the validity of the nomogram method seems to be problematic, death time estimates - and particularly their 95%-confidence interval limits - have to be interpreted carefully and should only be restrictively used as court evidence to support or refute alibis. Systematic overestimation of the post-mortem interval in bodies of high mass and large surface area must be taken into account.

Conditional probability distribution (CPD) method in temperature based death time estimation: Error propagation analysis

Bayesian estimation applied to temperature based death time estimation was recently introduced as conditional probability distribution or CPD-method by Biermann and Potente. The CPD-method is useful, if there is external information that sets the boundaries of the true death time interval (victim last seen alive and found dead). CPD allows computation of probabilities for small time intervals of interest (e.g. no-alibi intervals of suspects) within the large true death time interval. In the light of the importance of the CPD for conviction or acquittal of suspects the present study identifies a potential error source. Deviations in death time estimates will cause errors in the CPD-computed probabilities. We derive formulae to quantify the CPD error as a function of input error. Moreover we observed the paradox, that in cases, in which the small no-alibi time interval is located at the boundary of the true death time interval, adjacent to the erroneous death time estimate, CPD-computed probabilities for that small no-alibi interval will increase with increasing input deviation, else the CPD-computed probabilities will decrease. We therefore advise not to use CPD if there is an indication of an error or a contra-empirical deviation in the death time estimates, that is especially, if the death time estimates fall out of the true death time interval, even if the 95%-confidence intervals of the estimate still overlap the true death time interval.

Confidence intervals in temperature-based death time determination

Marshall and Hoares double exponential model with Henßges parameters is a well known method for temperature based death time estimation. The authors give 95%-confidence intervals for their method. Since body cooling is a complex thermodynamical process, one has to take into account a potential bias of the estimator. This quantity measures the systematic error of the estimators underlying model. For confidence interval radius calculation a bias of 0 is presupposed, therefore the actual probability of the true death time value to lie in the 95%-confidence interval can be much lower than 95% in case of nonvanishing bias. As in case of nonstandard conditions the confidence intervals have a probability of containing the true death time value which even in case of small corrective factor errors of Δ = ± 0.1 can be substantially smaller than the 95% claimed, the paper presents a formula for confidence intervals which keep a 95% probability in case of error Δc ⩽ ± 0.1.

The forensic relevance of hypothermia in living persons—Literature and retrospective study

In practical case work, forensic experts can be confronted with the problem of estimating cold exposure times in the living given the core body temperature after exposure. However, the current literature lacks systematic studies of body cooling in the living and cooling rates under different circumstances. The objective of our study is to provide working forensic specialists with a collection of cases to use for comparison in order to estimate the accident time or assault time using the cooling rates from similar cases. Excessive data mining led to 18 cases from the literature, 16 cases from Jenas patient files and 9 cases from the database of the Institute for Legal Medicine in Jena. Cooling rates between 0.15 °C/h and 4.1 °C/h were found in adults. Newborns showed rates between 1.2 °C/h and 28.5 °C/h. Potential factors that influence the cooling process in the living are discussed and the possibilities and limitations of the data acquisition and -evaluation are considered.

Calibration and parameter variation using a finite element model for death time estimation: The influence of the substrate

The most established method for temperature based death time estimation is based on an empirical double exponential model. New physically based approaches using numerical simulation techniques are subject of current research. A major advantage of such models is the possibility to incorporate non-standard boundary conditions. The aim of this study was to investigate the influence of the substrate on the cooling rate of a body in the early postmortem phase. A finite element model was used for parameter variation in terms of different substrate materials. Simulation results showed a considerable influence of substrate material on the postmortem cooling rate of a body. From a thermodynamical point of view, comparability between measurements on a steel trolley and real cooling scenarios with common substrates like normal floors, asphalt or soil remains questionable. It could be shown that not only the type of substrate but also its composition can have a considerable influence on the postmortem body cooling rate.

Fatal abdominal injuries in a bicycle-pedestrian collision – Reconstruction using multibody simulation

Fatal bicycle-pedestrian collisions do not occur frequently and thus are rarely reported in literature. Pedestrians in bicycle-pedestrian accidents often sustain severe craniocerebral injuries caused by a collision induced fall with head impact on the road surface. We describe a case where a pedestrian crossing a road was hit by a bicycle. Hematomas of the left lower leg and of the left flank/abdomen were found to be caused by the primary impact. However, the fatal injuries were found to be contralateral with a rupture of the right renal pedicle, a rupture of the right lobe of the liver and a tear of the vena cava. Neither the bicycle impact nor a fall onto the road surface could cause these injuries. Multibody simulation (PC Crash 9.2) revealed entanglement between the bicyclist and the pedestrian followed by a contact interaction between the pedestrian laying on the road surface and the falling bicyclist. In forensic case work post-crash contact interactions between the bicyclist and the pedestrian should be considered as a potential source of severe injuries.

Do multiple temperature measurements improve temperature-based death time estimation? The information degradation inequality

The accuracy of the input parameter values limits the accuracy of the output values in forensic temperature-based death time estimation (TDE) like in many scientific methods. A standard strategy to overcome this problem is to perform multiple measurements of the input parameter values, but such approaches are subject to noise accumulation and stochastic dependencies. A quantitative mathematical analysis of advantages as well as disadvantages of multiple measurements approaches (MMAs) was performed. The results areA general stochastic model of MMA.The information degradation inequality quantifying gains and losses of MMAs.Example calculations of the information degradation inequality for the following two MMAs relevant to TDE:o Multiple successive rectal temperature measurementso Multiple synchronous body layer temperature measurementsNeither multiple successive rectal temperature measurements nor multiple synchronous body layer temperature measurements seem to significantly improve death time estimation. MMAs are superior to the single measurement approach only in the very early body cooling phase.

Setting the boundaries of prior influence on kinship relation testing: the case of many hypotheses

Kinship relation and, in particular, paternity probability estimation using a Bayesian approach require the input of a priori probabilities of different hypotheses. In practical case work, a priori probabilities or priors, for short, must often be estimated using only common sense and symmetry arguments because in most cases, there is no evidence-based information on which the priors may be determined. In contrast to the accuracy of the likelihood probabilities or the likelihood ratios, the precision of the priors is usually very poor. Thus, a quantitative estimation of the priors’ influence on the paternity probability is desirable. This article presents exact formulae to define sharp minimum and maximum boundaries of posterior probabilities as a function of prior boundaries which may be applied in kinship cases with varying numbers of hypotheses and also presents two case examples.

Complete trunk severance of a motorcyclist by a traffic sign post at a comparably low collision speed

Traumatic limb amputations and transections of the trunk generally indicate high impact velocities. Complete traumatic severances of the trunk in road accidents however are rarely reported in literature. We describe a case where the trunk of a motorcyclist was completely severed as he hit the post of a traffic sign. Based on the documented end position and damage of the motorcycle, an impact velocity range of 52-80 km/h could be determined for the motorcyclist. To our knowledge, this is the first report on the type and mechanism of injury at this comparatively low collision speed range.