Abstract
The commonest way of killing in the UK is by a sharp instrument. Knight reported in 1975 that it is impossible to discern with any degree of certainty the degree of force used to create a stab wound. Despite this, expert witnesses continue to approximate the degree of force used for their reports and evidence in court. It is usually subjectively categorized as mild, moderate or severe, based solely on the examination of the wound. We undertook a study considering forces generated in a range of blunt trauma actions, using a novel force plate dynamometer to measure the peak forces obtained by adult male and female volunteers. We then studied forces generated by stabbing skin simulants and porcine samples with knives and screwdrivers. Men generated more force than women during stabbings which was found to be equivalent to somewhere between the blunt trauma actions of pushing a button to a single-handed push. When asked to stab using what they thought was mild, moderate and severe force, although volunteers were able to actively decide the force used, the actual force was found to be influenced by the weapon, sex of the individual, hand used and biological/anatomical site penetrated. This study shows that the forces generated by volunteers in mild, moderate and severe stabbing tests in almost all cases were significantly greater than the forces required for skin penetration. We suggest that the use of subjective force scales is inappropriate. Rather than use of a subjective scale, we suggest that the force required in any stabbing requires investigation in four areas: the tip radius of the weapon, minimal force required for penetration, the sex of the assailant and whether the force required for penetration is greater than that that can be generated by a person stabbing. This allows for the use of an evidence-based two-tier scale to suggest the force required.
Highlights
Knife crime continues to be a concern worldwide, in those countries where access to guns is restricted
Expert witnesses are often requested to approximate the degree of force used to cause the stab wound, as part of their statement and evidence provided to a court
The individual penetrative force for skin simulant, pork thigh and pork ribs as well as the blunt edge radii, tip radii and blunt edge tip angle for five steak knives and five all-purpose knives of the type used in the volunteer experiments as well as the flat-headed and Phillips-headed screwdrivers and the instrumented knife were investigated
Summary
Knife crime continues to be a concern worldwide, in those countries where access to guns is restricted. A subjective visual assessment of the sharpness of the blade may be taken into account Studies have been conducted previously to investigate the force involved in stabbings The earliest of these was by Knight in 1975, who found it impossible to answer the question with any degree of certainty [4]. The aim was to consider whether the use of the commonly used subjective scale is appropriate when providing evidence to a court concerning the possible forces used in stabbings, or whether a more scientific approach should be adopted by investigating the penetrative potential of the weapon itself
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