The Effects of Semen and Ignitable Fluid Processing Techniques on VIS-NIR Microspectrophotometer Fiber Analysis

Criminalists are tasked with the source attribution of evidentiary fibers by comparing class characteristics with know-source fibers. For example, the polymer type, length, optical properties, and color are discriminating characteristics considered during fiber comparisons. In practice, when textile fabrics are submitted as evidence, precedence is given to the detection and analysis of biological stains and other chemical residues prior to fiber collection and examination during evidence processing. This research investigates the effects of commonly employed semen and ignitable fluid processing techniques on VIS-NIR-Microspectrophotometer fiber analysis. Textile fabrics (including wool, cotton, silk, acrylic felt, polyester, rayon, acetate, olefin, and nylon) of different dye composition were selected as sample substrates. Presumptive screening was performed on semen-stained fabrics, including shortwave ultraviolet light exposure and acid phosphatase testing. In addition, the accelerant passive absorption elution method was replicated for each of the textile fabrics following their saturation with ignitable fluid. Fibers were recovered from each textile fabric pre-and post-application of the processing techniques and the dye components were analyzed using MSP with transmitted light in the visible and near-infrared region of the electromagnetic spectrum. The findings show that neither acid phosphatase nor UV semen testing have an effect on the color analysis of fiber samples using VIS-NIR MSP. The passive absorption elution method may cause a change in VIS-NIR MSP spectra characteristics, but further investigation is needed. Based on these findings, current laboratory procedures and the order of evidence processing methods are not an immediate concern for VIS-MSP fiber color analysis.