An Exploratory Time Since Deposition Analysis of Whole Blood Using Metrics of DNA Degradation and Visible Absorbance Spectroscopy

Abstract

Establishing the age of a bloodstain provides forensic investigators with critical information on the time that a crime occurred. Our work presents a time since deposition (TSD) analysis that integrates visible absorbance spectroscopy and high-resolution automated electrophoresis data to quantify light absorbance and DNA degradation of whole blood over time. Passive bloodstains were created and treated on either FTA cards without anticoagulant or in microcentrifuge tubes with anticoagulant and tested over 11 different timepoints across 15 days at controlled temperature and relative humidity. A total of 41 variables were analyzed using linear regression, with six variables showing statistical independence and a relationship to time. A general negative trend was noticeable for the visible absorbance of α and β bands and concentration of high molecular weight DNA of the samples over time. We then conducted a principle component analysis (PCA) of all variables; the principal components integrated both DNA and absorbance data and generally improved the model fit (i.e. increased R2). Importantly, our PCA findings demonstrated that the experimental effect of treatment and donor was largely accounted for in PC1, with PC2 reflecting the true relationship of the integrated metrics to time. Our data set and models are publicly available in an effort to build upon this study by incorporating environmental variables.