RESUMO
Forensic taphonomy as a discipline requires standardization to satisfy Daubert criteria for scientific data to be admissible in court. In response, there has been a shift towards quantification of methodology and estimating the postmortem interval. Despite these advances, there are still biases and limitations within the discipline not explicitly addressed in the early stages of experimental design nor in final published works. In this article, unresolved debates with respect to the conductance and reporting of forensic taphonomic research are reviewed, beginning with the nature of experimental cadavers, human or animal analogues and their body size, and second, the forensic realism of experimental setups, specifically with respect to caging, clothing and number of carcases. Pigs, albeit imperfect, are a good model to gain a general idea of the trends that may be seen in humans in subsequent validation studies in facilities where human donors are available. To date, there is no consensus among taphonomists on the extent of the effect that body mass has on decomposition progression. More research is required with both human cadavers and non-human analogues that builds on our current knowledge of forensic taphonomy to answer these nagging questions. This will enable the discipline to make the reliable assumption that pigs and donor decomposition data can be applied to homicide cases. A suite of experimental design aspects is suggested to ensure systematic and standardized data collection across different biogeoclimatic circumstances to identify and quantify the effects of potential confounding variables. Such studies in multiple, varied biogeographic circumstances with standardized protocols, equipment and carrion will facilitate independent global validation of patterns. These factors are reviewed to show the need for adjustments in experimental design to ensure relevance and applicability of data within locally realistic forensic situations. The initiation of a global decomposition data network for forensic taphonomists is recommended.Key pointsPigs are a valuable, albeit imperfect, proxy for human decomposition studies.There are few or conflicting data on effects of carcase size, carrion ecology, exclusion cages and scavengers.We recommend single, clothed, uncaged carcases for baseline research to reflect regionally specific forensic casework.
RESUMO
In forensic death investigations, estimating the postmortem interval (PMI) is critical. An accurate PMI estimate increases the speed and accuracy of identifying the remains by narrowing the time frame in which the death occurred, thus reducing the pool of possible decedents. Cape Town, South Africa has a high level of unnatural death, and due to a burdened death investigation system, many remain unidentified. There has been a tendency to broadly apply quantitative models of decomposition across biogeographically unique circumstances. A prime example is the widespread application of the total body score (TBS)/accumulated degree day (ADD) model developed by Megyesi et al. (2005), later refined by Moffatt et al. (2016). However, the appropriateness of applying a single model to a wide range of locations with unique geography and climates remains in question. The aim of the study was to evaluate and compare the accuracy of Megyesi and Moffatt models for estimating PMI in Cape Town, South Africa. Using pig carcasses, Finaughty established baseline data on the rates and patterns of terrestrial decomposition in summer and winter in two different locations in a forensically significant area of Cape Town. Among the baseline data, Finaughty derived TBS values using the Megyesi criteria. The present study used these values to estimate the ADD per the Megyesi and Moffatt models, which would correspond to an estimated PMI. These estimated values were compared to actual ADD values. Estimates of ADD were inaccurate for both models in winter, and only partially in summer. The Moffatt model was more accurate in earlier decomposition stages, with the Megyesi model more accurate in later decomposition stages. These results indicate the Cape Town environments may contain factors that the two models do not consider, producing inaccurate PMI estimations at various TBS' values. ADD does not depict the entire taphonomic story; the decomposition process appears to be too complex for universal modelling based on a single or narrow suite of variables. Seasonality was an important factor in determining the accuracy of the models, primarily resulting in underestimations of the true PMI values. These findings show the impracticality of applying models developed for- or in one region to any other and support the need to establish regionally-specific equations for estimating PMI in a forensic context. Alternatively, more complex models employing "big data" from a more comprehensive suite of variables which influence the rate and pattern of decay could be developed.