Development and evaluation of an IR standoff spectrometer prototype for rapid crime scene forensic surveying

A common need across crime scene investigators is the ability to quickly identify forensic-relevant elements at the scene and prioritize trace collection. This is particularly evident at early stages of a crime scene investigation, increasing awareness and also potentially reducing safety risks induced by exposure to hazardous substances. Here, a standoff spectrometer prototype for in-situ forensics is presented. The measurement principle is diffuse-reflectance spectroscopy in the mid-infrared (IR). At a standoff distance of up to 1.5 m, targets (points of interest selected by forensic operators) are illuminated by two multiplexed IR lasers and the measured diffuse reflectance spectra are classified in real time. The prototype’s performance towards the intended application in preliminary crime scene survey is evaluated by testing a range of substances of forensic interest including blood, explosives, drugs of abuse, precursors, adulterants, cutting and bulking agents. Time-uninterrupted measurements with millisecond-resolution are presented and discussed. Good detection and selectivity results were obtained for the vast majority of the investigated samples. Strong potential is found for the preliminary identification of blood at the crime scene, distinguishing it from potential interferents.