Principles of tool mark analysis and evidential best practice

The interpretation of tool marks is an important component of many forensic investigations and can impact on a variety of disciplines, including anthropology, archaeology and pathology. The definition of tool mark analysis is not precise, but generally refers to the detection, enhancement, comparison and evaluation of marks/indentations left behind on a substrate after contact with a tool or implement. The study of marks produced by weapons/instruments/tools within criminalistics is most commonly employed in the investigation of crimes involving the forced opening of lockfast items or premises (May, 1930; Burd and Kirk, 1942; Burd and Greene, 1948; Bonte, 1975), but an equally important facet of tool mark examination is the identification of an implement used during acts of fatal interpersonal violence (Marciniak, 2009). This is pertinent irrespective of whether these acts are committed before (injury) or after (dismemberment/disfigurement) the death of the victim (Puentes and Cardoso, 2013). In forensic cases related to dismemberment, the marks left by the implement represent dynamic (cutting or multi-stroke) marks that are distinct from static marks, which result when a tool is pressed into a softer material, leaving behind an impression, or the impact patterns resulting from blunt or sharp force trauma. Dynamic marks are made either when a single bladed tool slides across a surface, or when a cutting tool has been used to partially or completely cut/sever an object. Although it is recognized that dismemberments can occur through accidental means, for example, forceful trauma such as hanging, vehicular strike or explosion, in the context of dismemberment for this text, we refer only to the intentional use of a tool or instrument to cause separation of body parts.