Variability and specificity of bone cutting mark properties in cases involving stabbing with knives

Sharp force traumas are frequently encountered in stabbing crime victims. During an examination, the properties of cutting marks in bones are compared with the properties of suspect tools, particularly knives. Therefore, the variation and specificity of knife and cutting mark properties must be known. This article provides the variability and specificity of a set of knife blade and cutting mark properties. Plain and serrated knives are used to create experimental cutting marks in porcine ribs, knife properties are derived from surface acquisitions of the blades and mark properties from Micro-CT data. We consider two conditions, automated stabbing using a motorized stage and manual stabbing. In addition, we study the influence of maceration on marks. For knives, the blade edge angle, blade thickness, and bevel height, and for cutting marks, the shape, the wall angle, the width, and the bevel height are determined and compared. The results show that the relationship between corresponding properties of blades and marks depends on the knife type. For plain knives, the width and wall angle of the marks are dependent on the mark depth and are significantly smaller than the blade properties edge angle and width. For serrated knives, this is not the case. The mark shape only provides slight support for a knife type for marks deeper than the blade bevel height. In conclusion, mark properties are only specific for a particular knife brand and model if the blade properties differ significantly and assuming a specific knife type.