Forensic examination of lipsticks as trace evidence under different environmental conditions

Abstract

Trace evidence such as fingerprints, biological fluids, fibres, glass, hairs, soils, and cosmetics have been considered most of the important materials on the crime scene, which can be potentially transferred or exchanged between two surfaces when one makes contact to another. Cosmetic products are one of the valuable trace pieces of evidence on crime scene that are generally used for beautification, moisturize, reinforcement of the skin, nutritiveness, and improve the feeling or sensory aspects. In this study, different lip cosmetic products including wax lipstick, liquid lipstick, gloss and lip balm were investigated as forensic evidence. For this, 102 of lip cosmetic samples (20 of lipstick, 14 of lip gloss, 22 of lip balm and 46 of liquid lipstick) were analyzed by using Fourier-transform Infrared spectroscopy (FTIR). The differentiation between lip cosmetic products is detected. The effect of environmental conditions is studied. For this, lip cosmetic products are kept in various water medium such as simulated sea water, tap water, and distilled water in order to track the chemical stability by FTIR. Moreover, they are kept in different time of intervals from 1 day to 1 month to investigate the change over time. Staining of lip products to various substrates including fabric, glass and paper towel have been also explored. The effect of substrate type, lip cosmetic products, time and water sources have been systematically explored by FTIR and video spectral comparator (VSC). All the samples have been examined under different light sources such as visible light, UV-A (365 nm), infrared (695 nm) and spot (fluorescence) to observe the distinctive features of lip cosmetic samples on different substrates. The results have demonstrated that lip products including wax, liquids lipstick, gloss and lip balm have distinguishing character which is observed by FTIR and VSC8000. Moreover, the chemical stability of lip cosmetic products under different water sources could be characteristic tools for differentiating of lip cosmetic products. The outcomes show that cosmetic trace evidence found in water source could be critical evidence in crime scene investigation.