Aging discrimination of multispecies bloodstains on realistic forensic substrates using vibrational spectroscopy and chemometric models

Bloodstains found at crime scenes, mainly in violent cases, can have various origins. Human bloodstains are usually the most relevant; however, the large number of domestic animals currently living in homes can also lead to the presence of animal bloodstains at crime scenes, especially when the committed crime has involved an animal. Determining when the bloodstain was deposited, whether human or animal, is essential for reconstructing the events. The use of non-destructive analysis techniques that allow the integrity of the evidence to be maintained for subsequent analyses is becoming increasingly important. Thus, this study seeks to examine and compare the use of attenuated total reflectance-Fourier transform infrared (ATR-FTIR) and Raman spectroscopy, together with chemometrics, for the estimation of the age of human, dog, and cat bloodstains when they are found deposited on complex substrates such as sand and soil. No visual changes were observed in the bloodstain spectral bands over time, especially when deposited on the complex substrates. Thus, orthogonal partial least squares-discriminant analysis (OPLS-DA) models were created to classify bloodstains according to their time since deposition (age). It was possible to distinguish the bloodstains according to their different age, regardless of the donor's species and on the complex substrates considered in this study, both with ATR-FTIR and Raman. These are promising results for investigating real forensic situations, such as bloodstains found in burials.