Accuracy of Area of Origin Analysis on Textured, Wallpaper Surfaces

Bloodstains at crime scenes can be deposited or projected on many surface types, and the importance of Area of Origin (AO) calculations for impact stains are vital in the sequence of events. In the UK, wallpaper is a common material used to decorate walls. This study looked at the effect different wallpapers had on the calculated Area of Origin (AO) using FARO Zone 3D (FZ3D) software. A variety of wallpaper types were used, such as Foil, Printed, Vinyl, Washable, Woodchip and Anaglypta. These consisted of smooth and rough surface textures while the control was a plain painted wall. For each wallpaper type and control plain wall, six repeated impacts were conducted. An impact rig with a spring tension arm was fixed 45 cm from the X wall and 45 cm from the Y wall, and remained the same throughout the experiment, to resemble an impact blow for a bloodletting event. The location was also known to the analyst. AO error co-ordinates were measured directly in the FZ3D software to the known impact location, and the results were analysed. An overall 30 cm maximum allowable error from the known impact location was chosen since it was expected that textured surfaces would not perform as well. Nonetheless, 30 cm can still distinguish between a person that is low to the ground, kneeling or standing. The mean AO errors for each wallpaper type were Plain wall, 9.77 cm, Anaglypta wallpaper, 18.55 cm, Woodchip wallpaper, 13.99 cm, Washable wallpaper, 9.81 cm, Foil wallpaper, 10.82 cm, Printed wallpaper, 10.77 cm and Vinyl wallpaper, 9.59 cm. The maximum error for any one impact test was 24.81 cm which was within the chosen 30 cm limit. Wallpapers that had highly textured surfaces had the greatest errors. Also, FZ3D is shown to be an acceptable tool when analysing impact bloodstain patterns on different wallpaper types.