A preliminary investigation to determine the suitability of pigs as human analogues for post-mortem lipid analysis

• Pigs are not equal to humans when analyzing post-mortem lipids in textiles. • Statistically significant interspecies differences are driven by the formation of adipocere. • Statistically significant interspecies differences were observed for both Australian summer and winter environments. • Post-mortem lipids in textiles are a suitable biomarker for monitoring decomposition. The determination of time since death is a major challenge to law enforcement when faced with the discovery of human remains. This is due to the fact that decomposition is a complex, dynamic process influenced by several abiotic and biotic factors. For decades, post-mortem decomposition studies have used pigs as human analogues due to ethical and legal restrictions surrounding the use of human cadavers for such research. However, few comparative studies have been conducted to assess the suitability of these analogues. Recent forensic studies have successfully demonstrated the use of post-mortem lipids in textiles as a method to obtain vital information about decomposition process. The current investigation involved two studies: Trial 1 (summer) and Trial 2 (winter). Each trial with n = 1 human cadaver and n = 2 pigs. Samples were collected over a timeline of 105 days post-placement and analyzed using attenuated total reflectance (ATR-) Fourier-transform infrared (FTIR) spectroscopy. The data was then statistically assessed using functional principal component analysis, semi-parametric regression modeling and analysis of variance. The results demonstrated a clear statistically significant interspecies difference between pigs and humans in both trials. The preliminary implications of this study suggest that pigs are not suitable analogues for humans in decomposition research and have broader implications that caution the direct translation of decomposition data obtained from pigs to real human casework, particularly with respect to time since death estimations.