What is the primary purpose of using Small Particle Reagent in latent print development?

The primary purpose of using Small Particle Reagent (SPR) in latent print development is to process wet nonporous materials. SPR is particularly effective in revealing latent fingerprints on surfaces that have been contaminated with water or other liquids, where traditional methods might fail. This reagent works by adhering to the lipids within the fingerprint residue, making the prints visible, even in wet conditions.

The other options represent different methods or reagents used for specific purposes but do not accurately describe the primary application for SPR. For instance, developing prints on porous surfaces typically involves techniques like chemical treatments that react with the components in the paper or cloth. Staining proteins in blood is associated with other reagents designed for forensic biology applications rather than latent print analysis. Fluorescing natural latent fingerprints is usually achieved through different fluorescent powders or laser techniques, which are not the main role of SPR. Thus, the effectiveness of SPR is unique to nonporous surfaces that are wet, making it an essential tool in forensic investigations.