During a recent high-profile criminal trial, headlines appeared in the national newspapers stating that the victim had ‘walked into the knife’. While this scenario was surprising for some, for those working in forensic medicine, this situation poses a well-known difficult challenge.
[caption id="attachment_30872" align="alignright" width="300"] Figure 1a: Experimental stab-penetration test rig[/caption]
When a stabbing is fatal, the amount of force required to inflict a stab wound is often the source of much debate in court. The forensic pathologist usually assesses the force exerted based on the condition of the blade, the extent of the tissue damage, the presence of clothing and other factors, and describes the level of force as ‘mild’, ‘moderate’ or ‘severe’. This information is then used by the jury to assess the degree of intent of an assailant. In certain specific situations, it can be difficult, if not impossible, to distinguish between a walk-on or run-on scenario and a thrust action.
This situation prompted Dr Mike Curtis and Prof Marie Cassidy in the Office of the State Pathologist to team up with Prof Michael Gilchrist and Prof Michel Destrade (now at NUI Galway) in the School of Mechanical & Materials Engineering at UCD in order to develop a quantitative measure of the force involved in puncturing skin. The objectives of the research, completed by Dr Aisling Ní Annaidh as part of her PhD thesis, at first appear to be simple: