Investigating the formation of faux bloody fingermarks: the influence of secretion type and blood deposition mechanisms

In a criminal case, a bloody fingermark located at a crime scene can provide high evidentiary value as the fingermark pattern and DNA profile from the blood can both be used for context and identification purposes. Probative evidence of this nature is scrutinised in court. One question that is often raised is the possibility that a bloody fingermark at a crime scene is a faux bloody fingermark, meaning that a latent fingermark was present at the scene before a bloodshed event, and that the blood has ‘developed’ the latent fingermark. Unfortunately, research available to fingerprint experts to help them answer this question is limited and inconclusive. This project is a pilot study that aimed to develop a method to better understand how bloody fingermarks form, focusing on faux bloody fingermarks, as a starting point. This project investigated various SWGSTAIN bloodstain mechanisms and fingermark residue compositions to find combinations in which faux bloody fingermarks were likely to form. The resulting faux bloody fingermarks were assessed for quality using the CAST grading scale. As a result, it was observed that in the majority of cases, faux bloody fingermarks were not formed. In instances where faux bloody fingermarks were formed, this relied on a combination of sebaceous-rich fingermarks and flow and swipe bloodstain mechanisms. These types of fingermarks have the potential to be confused with genuine bloody fingermarks and more research should be conducted to explore if and how faux bloody fingermarks can form under a wider set of conditions. • The formation of faux bloody fingermarks is highly variable. • Sebaceous-rich fingermarks were more likely to result in faux bloody fingermarks. • Eccrine-rich fingermarks did not form faux bloody fingermarks. • Faux bloody fingermarks are more likely to form when blood moves over a fingermark.