Drowning and postmortem immersion identification using attenuated total reflection-Fourier transform infrared spectroscopy

Abstract

It remains a major challenge for forensic practice to accurately distinguish whether a corpse in the water died from drowning or postmortem immersion. When the corpse is severely decomposed, the problem becomes more complicated. In this study, we utilized attenuated total reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR) and chemometrics to distinguish whether a corpse in the water died from drowning or postmortem immersion. The results of Principal Component Analysis (PCA) showed that there was a certain degree of difference between the freshwater group and the saltwater group due to the different concentrations of drowning medium, and the degradation of lung tissue had no significant effect on the differentiation between drowning and postmortem immersion. Amide I and amide II contribute to the distinction between drowning and postmortem immersion. Subsequently, we constructed partial least squares discriminant analysis (PLS-DA) models for the identification of drowning and posthumous immersion in the freshwater group and the saltwater group, respectively. Both models showed good classification capacity, with the accuracy rates of 94.4% and 100%, respectively. As to results of average second derivative spectroscopy, PCA and PLS-DA all indicate that the difference in protein structure and content is the key to distinguish between drowning and postmortem immersion. This pilot study demonstrates that ATR-FTIR in combination with chemometrics has the potential to be an effective method for distinguishing between drowning and postmortem immersion.