How can it be determined whether a person has died by suicide or homicide - an assessment that is key to the legal process? A new thesis from Lund University in Sweden shows how forensic medicine can become more accurate and legally sound by relying on systematic data rather than professional experience alone.
In her thesis, Maria Berg von Linde, a recent doctoral graduate from Lund University and a forensic pathologist at the National Board of Forensic Medicine in Lund, has analysed a large national dataset from the National Board of Forensic Medicine comprising both fatal and non-fatal cases involving a single stab wound to the trunk.
"We realised early on that there was a lack of scientific evidence in one type of case that can be difficult to assess, namely single stab wounds. There are often no clear injury patterns, which makes it difficult to determine what has happened - whether the person inflicted the injury on themselves or whether someone else did it," says Maria Berg von Linde.
The answer is of great importance to the legal process, as it determines whether or not a crime is to be investigated. An incorrect assessment has implications for legal security, as in the worst-case scenario it could result in a perpetrator going free or an innocent person being convicted. These assessments are also important for relatives and social preventive work.
Differences between homicide and suicide
Although the assessment is not straightforward, studies have identified generalisable patterns that can assist forensic pathologists in their assessments:
- Homicide victims are more often young men who are attacked outdoors.
- Homicide victims are more often under the influence of alcohol or illegal drugs.
- Suicides are more likely to occur at home.
- Self-inflicted stab wounds are usually found on the front of the trunk, whereas in homicide cases the stab wounds are scattered across the entire trunk.
"By analysing the injuries and circumstances within a large population, we can identify patterns that can then be used to assess individual cases - and this enables us to base our assessments on a more systematic approach, while also making the evidence available for external review," says Maria Berg von Linde.
New tool could assist forensic pathologists
As part of the research, a new assessment tool - MODSIT (Manner of Death in Stab Injuries to the Trunk) - has been developed, which takes several factors into account to distinguish between homicide and suicide. The tool has demonstrated a very high degree of accuracy in the studies.
"It is not intended to replace expert judgement, but can serve as a tool to help ensure more consistent and transparent assessments."
The thesis also demonstrates that an established trauma scoring system can be used to determine whether an injury has been life-threatening, which is a key issue in legal proceedings involving survivors of stab wounds, as it may influence how serious the offence is deemed to be and the sentence received by the perpetrator.
Research that strengthens legal security
Supervisor Carl Johan Wingren believes that the thesis highlights an important development in forensic medicine:
"Forensic assessments are largely based on experience and professional judgement. This type of research makes it possible to move towards a practice where assessments are consistent and evidence-based," he says, emphasising that the research is also significant outside the field of forensic medicine.
"At its core, it's about legal security. Forensic reports can be of crucial importance in a court case, and it is therefore important that assessments are as robust and transparent as possible, so that the court can understand the strengths and weaknesses of the reasoning."
How MODSIT works
MODSIT (Manner of Death in Stab Injuries to the Trunk) is a research-based assessment tool that helps forensic pathologists determine whether a stab wound was caused by homicide or suicide.
- It is based on an analysis of national forensic data from both fatal cases and verified survival cases.
- It takes into account various types of information, such as the characteristics of the injury (e.g. placement, direction of the entry wound and defensive wounds), circumstances at the scene (e.g. indoors/outdoors, location of the knife after the incident), influence of alcohol, and demographic factors (age and gender).
- Each variable was assigned a score based on how specific it is to homicide or suicide cases. The accuracy of the scoring system was evaluated using a statistical model (known as receiver operating characteristic analysis).
- The results clearly indicate whether the evidence points to homicide or suicide.
- The tool is intended to serve as a support and to be used in conjunction with forensic pathologists' expert assessments in order to enhance transparency and consistency in their assessments. The method has been developed using Swedish data and needs to be validated in other populations.
