An evaluation of infrared photography for detecting bloodstains on dark-coloured floor coverings commonly encountered at crime scenes

The ability to accurately detect bloodstains is fundamental to crime scene examination; however, traditional methods can be inadequate for use on many dark-coloured surfaces commonly encountered at scenes, such as fabrics and flooring. An alternative approach may be the use of infrared (IR) photography, which is known to be effective at detecting bloodstains on fabrics and some non-porous surfaces. However, a knowledge gap exists concerning the effectiveness of IR photography for detecting bloodstains on dark-coloured floor coverings. To address this, we used a paired sampling design to assess the performance of IR photography compared with tetramethylbenzidine (TMB) and luminol for detecting bloodstains on wool and nylon carpet, linoleum, vinyl, tile and laminate flooring. We also assessed whether IR imaging would detect a substance known to create false-positive reactions with TMB and luminol. Overall, our results supported IR photography as an effective, non-destructive method compared to TMB and luminol for detecting bloodstains on dark-coloured flooring, especially nylon carpet, tile, laminate and vinyl. Further, IR did not detect known false-positive samples on several surfaces. This research contributes to a growing body of literature concerning the forensic applications of IR photography and has significant operational implications for crime scene examiners.