Crime scene investigation II: The effect of warfarin on bloodstain pattern analysis

Abstract

We explore for the first time the effect of medical drugs on Bloodstain Pattern Analysis (BPA). The widely administrated anticoagulant warfarin is examined with its effect on blood viscosity measured using a capillary tube viscometer over the range of 10⁻⁶ M to 10⁻⁴ M, representing therapeutic to fatal levels respectively. We find that the administration of therapeutic to fatal doses corresponds to a viscosity change of 3.6 to 20.4% respectively. Additionally the effect of warfarin on blood's surface tension, usually assumed to be constant, is examined over the therapeutic and fatal dosage range, which was found to result in a change of between 0.6 and 4.7% respectively. The observed variability's were integrated into previously derived BPA equations used for de-convoluting various parameters where convincing evidence is shown that drug contaminated blood induces a variation of 1.23 mm (5.93%) in the determined final stain diameter leading therefore to the possible misinterpretation of bloodstains found at Crime Scenes and consequently inaccuracies to occur in crime scene reconstruction. This work offers insight into whether medical drugs play a significant role in the possible misinterpretation of bloodstain evidence.