Enhancing bloodstain visibility on dark surfaces: Specificity and sensitivity of infrared photography for detecting bloodstains

Low power microscopy and additional light sources are the standard tools used for searching items for blood in forensic casework. This process can be time-consuming and can yield limited information when examining dark surfaces due to poor contrast between bloodstains and the surface. This research investigated the specificity and sensitivity of Infrared (IR) photography in visualising various bloodstains on multiple dark surfaces using the Canon XA60 IR Camcorder. The specificity studies involved the comparison of the IR visualisation of neat blood and common substances found in casework (such as, mud, rust, lipstick, tomato sauce, marker pen, semen, urine, and saliva). To examine the sensitivity of the technique, dilutions of blood and water were created to determine the detection limit of the IR Camcorder. Among the substances tested, mud and rust were found to be absorbers of IR and appeared similar to blood, however they were readily discriminated in white light from bloodstains. In comparison to other body fluids, blood was the only sample that absorbed IR. Semen, urine and saliva reflected the IR. The detection limit of IR visualisation was up to 1:10 dilutions and occasionally 1:12 dilutions were visualised, but this was not consistent. Further studies revealed that exposure to IR does not influence or cause DNA degradation. In conclusion, this study found IR photography to be an efficient tool for blood searching as well as post-search enhancement and documentation.