Chapter 14: Identification of Semen

The identification process begins with presumptive screening techniques, which include visual examination enhanced by alternative light sources that exploit the natural fluorescence properties of seminal material. The acid phosphatase colorimetric assay represents the classic presumptive test, though practitioners must recognize its limitations and potential for false positive results from other biological sources. Confirmatory identification traditionally relies on microscopic examination to detect and characterize spermatozoa, establishing definitive proof of semen presence. However, many forensic samples present obstacles to this classical approach, including azoospermic cases where sperm cells are absent or severely depleted. In these scenarios, forensic scientists employ protein-based biomarkers that provide reliable identification independent of sperm presence. Prostate-specific antigen, also known by its gene designation KLK3, demonstrates high specificity to seminal fluid and can be quantified through enzyme-linked immunosorbent assay or rapid membrane-based immunochromatographic tests. Seminal vesicle-specific antigen, chemically identified as semenogelin, serves as an additional proteinaceous marker that confirms seminal origin through various immunoassay platforms. Contemporary forensic serology has evolved to incorporate molecular techniques that analyze messenger ribonucleic acid profiles from seminal samples. This RNA-based approach targets protamine messenger transcripts, specifically the PRM1 and PRM2 variants, alongside KLK3 messenger expression, offering enhanced sensitivity and specificity compared to protein detection alone. These molecular markers provide particular advantage in degraded samples or situations where protein analysis yields ambiguous results. The integration of presumptive screening, confirmatory microscopy, protein immunoassays, and mRNA profiling creates a robust analytical hierarchy that accommodates the variable nature of real-world forensic evidence while maintaining scientific rigor and legal defensibility in criminal investigations.