Criminalistics Chemical Determination of Sex from Dermal Prints

Abstract

Sex determination from trace evidence is a crucial tool for guiding criminal investigations. The chemical exploitation of fingermarks, specifically the amino acids in sweat, represents a promising alternative. This study addresses this issue through the comprehensive validation of two alternative analytical methods based on UV-Visible Spectroscopy. The objective was to develop and statistically validate the enzymatic and colorimetric methods for the quantification of amino acids in fingermarks, evaluating their discriminative power for sex determination, their robustness against operational variables (surface, developing agent), and their applicability in real casework. A phased experimental design was implemented: stochastic simulation of 100 amino acid profiles based on a log-normal distribution from bibliographic data, systematic optimization of spectroscopic parameters, method validation according to international protocols, analysis of discriminative power using non-parametric inferential statistics, and operational validation with 1800 experimental marks and 60 real fingermarks from criminal archives. As results, robust optimal conditions were established (Enzymatic: λ=436 nm, T=40°C, t=30 min; Colorimetric: λ=570 nm, T=40°C, t=35 min). Both methods demonstrated linearity (R² > 0.997), precision (CV < 1.5%), and accuracy (p > 0.01 in mean comparison tests). Statistical analysis confirmed highly significant differences (p < 0.001) in amino acid concentrations between sexes, with concentrations approximately doubled in females. Validation with real fingermarks yielded an efficacy of 96.6%. The nature of the receiving surface and the physical developing agent showed no statistically significant influence on the determination.