Light for Crime Investigation

The identification and quantification of material present and collected at a crime scene, including their comparison against known standards, are critical requirements in investigative analyses. Forensic analysts use a variety of tools and techniques to achieve this. In this lecture, light is presented as one of the key elements in crime investigation. Light of selected wavelengths and instruments based on light technology are powerful tools in crime investigation (light as a “friend”) for detecting DNA, spores, polymers, fibres, glass, gunshot residues and drugs of abuse. On the other hand, light can degrade samples of utility in investigative analyses, i.e., UV light breakage of DNA during DNA profiling, and sunlight may alter crime investigation results when outdoor samples are collected and then subjected to forensic analyses (light as a “foe”). At the same time, the adverse effects of light on evidence of materials of interest could open opportunities for development of additional markers not yet explored or enrichment of libraries of dedicated instruments by adding degradation products to reduce false negative or false positive results. Therefore, this lecture will critically review the available methods of crime scene investigation which exploit light, discussing their advantages and limitations.