Paint it white: Non-toxic white powder suspensions for enhancing bloody fingermarks on dark substrates

Bloody fingermarks serve as critical evidence in forensic investigations; however, their detection on dark substrates remains a challenge for practitioners. Although some highly effective methods exist for visualising such marks, they can have limitations and are generally protein dye treatments delivered in multi-step fixing and staining processes. In contrast, wet powder suspensions are commonly used to develop latent fingermarks on the adhesive side of tape, and some limited research has demonstrated their effectiveness in detecting bloody fingermarks. However, existing methods typically rely on commercially available products or methanol-based powder suspensions, which pose flammability and toxicity risks. This study evaluated the effectiveness of a simple, water-based, laboratory-prepared white powder suspension for detecting bloody fingermarks across various surfaces. Experimental results demonstrated that suspensions formulated with white fingerprint powder effectively visualised bloody fingermarks. A comparison study indicated that viscosity and the inclusion of a surfactant had minimal impact on fingermark quality, with the laboratory-prepared suspensions performing comparably to a commercial product. Further experiments revealed that higher-viscosity formulations yielded optimal development on complex substrates and that describing the desired consistency as "thick paint" was sufficient guidance for a fingerprint expert and a scenes-of-crime officer to successfully develop the majority of the bloody fingermarks in a blind pseudo-operational study. Laboratory-prepared white powder suspensions present a novel and practical approach for detecting bloody fingermarks on dark surfaces, expanding forensic capabilities and offering an accessible, cost-effective alternative for resource-limited jurisdictions in alignment with frugal forensic principles.