Puncturing a castle defence: injury biomechanics solution to a homicide investigation case study

In the wake of a homicide, investigators were confronted with a castle doctrine self-defence argument that was difficult to refute with the tools and evidence at their immediate disposal. However, in his confession, the suspect claimed to have caused the stab wounds in an unusual manner. The victim's autopsy revealed that one of the stab wounds pierced the sternum and cut into the victim's heart, while another cut between ribs and stopped only at the knife hilt, causing a rib fracture. To provide insight into the likelihood of the suspect's narrative, investigators turned to injury biomechanics. It was possible to show the suspect's version of events had a low to an impossible chance of occurring through quantitative testing relating to sternum stabbing, rib fracture load, and ergonomic analysis, ultimately leading to a change in plea to 3rd-degree murder. This case illustrates the worth of injury biomechanics when dealing with complex homicides and why the standard investigative toolbox should include it.