Increasing the efficiency of rape investigation by using advances in forensic evidence analysis
In criminal cases, a DNA profile recovered from an item can link a suspect to the crime scene. However, the DNA profile itself can only provide information to help identify the donor of cellular material and does not explain how (direct or indirect transfer) or when (before, during or after the crime event) the cellular material was deposited.
In court, alternative propositions are considered to explain evidence. To establish the value of the evidence in relation to activities, the scientist considers different transfer mechanisms of cellular material to describe how a defendant’s DNA came to the crime scene given alternate propositions. However, evaluation of the evidence is often inadequate because of limited knowledge of transfer and persistence of cellular material. This is because there has been insufficient research in this area. In addition to questions related to how and when a DNA profile was deposited, the question about the type of body fluid/cells that the DNA profile originated from can be of great importance. For instance, in a rape case, where DNA from the victim is found on a penile swab recovered from the suspect, the confirmation of the cell-type is paramount to the investigation. The prosecution will propose that a sexual assault was committed by the suspect, and DNA from the victim was transferred as a result. The alternative (defense) explanation may be that the findings are a result of indirect transfer after social contact i.e. the DNA comes from epithelial skin cells from the victim and not vaginal epithelial cells as argued by the prosecution. Hence, the detection of a body fluid can provide additional information of activity required for its deposition.
In this PhD project we will investigate transfer, persistence and recovery of DNA and body fluids (gene expression markers) in samples collected from body and clothing after social contact and sexual contact. This knowledge is essential to evaluate the findings in cases related to sexual assault cases. In addition a method that can link a body fluid to a specific contributor to a crime stain, containing DNA from two or more individuals, will be attempted.
The aim of this project is to develop tools that will aid interpretation and understanding of DNA traces at activity level in sexual assault cases. The study will comprise a large dataset that will be made available for other scientists and police to aid in sampling and interpretation of evidence under different case circumstances. The dataset will further be used to address the weight of the evidence given the alternative explanations of activities that are raised by the prosecution and the defense. This will be communicated by using an activity related Bayesian Network as an objective tool that will help the forensic scientist and court to interpret the evidence.
The results will be disseminated via training packages to scientists, police, lawyers and judges.