A Practical Guide for the Formulation of Propositions in the Bayesian Approach to DNA Evidence Interpretation in an Adversarial Environment

The interpretation of complex DNA profiles is facilitated by a Bayesian approach. This approach requires the development of a pair of propositions: one aligned to the prosecution case and one to the defense case. This note explores the issue of proposition setting in an adversarial environment by a series of examples. A set of guidelines generalize how to formulate propositions when there is a single person of interest and when there are multiple individuals of interest. Additional explanations cover how to handle multiple defense propositions, relatives, and the transition from subsource level to activity level propositions. The propositions depend on case information and the allegations of each of the parties. The prosecution proposition is usually known. The authors suggest that a sensible proposition is selected for the defense that is consistent with their stance, if available, and consistent with a realistic defense if their position is not known.     

Evaluating DNA profiles in a case where the defence is "it was my brother".

The widespread application of DNA profiling has brought to some prominence the issue of close relatives sharing body fluid types. In a particular crime case it may be suggested that a close relative of the suspect was the person responsible. This paper explains how an assessment may be made in the context of single locus profiling and where the suggestion is that a full sibling is involved. A formula is established for the likelihood ratio which is then worked out in detail for the particular case where the suspect profile has two distinct bands. Generalization to other types of case is briefly explained and there is a short discussion of the impact of the evidence in the context of a trial. For all parties, justice will best be done if the scientist has ample notice, before the trial, of relationship issues such as this one.     

Perceptions of restorative justice concepts: an evaluation of university housing residents

This study focuses on the perceptions of students who resided in a university residential hall regarding methods of conflict resolution and concepts of restorative justice. Furthermore, comparisons of perceptions between residents who participated in restorative justice workshops with residents who did not are also made. Variables studied include: understanding the perspectives of others, willingness to approach others, consideration of how to approach others, and awareness of communication styles during conflict situations. Additional considerations include a willingness for inclusion, providing perspectives, and listening and compromising during conflict situations. Also explored is usage of dialogue as well as residents becoming better equipped to approach others, and utilizing or sharing information about restorative justice concepts with others following restorative justice workshops. Findings suggest that residents exposed to restorative concepts during workshops were more likely than non-attenders to listen to the perspectives of others regarding conflict situations. The results indicate that a number of the residents within the university housing setting shared and utilized restorative justice techniques with others following attendance of the restorative workshops.     

Quantitative assessment of evidential weight for a fingerprint comparison. Part II: a generalisation to take account of the general pattern

The authors have proposed a quantitative method for assessing weight of evidence in the case where a fingermark from a crime scene is compared with a set of control prints from the ten fingers of a suspect. The approach is based on the notion of calculating a Likelihood Ratio (LR) that addresses a pair of propositions relating to the individual who left the crime mark. The current method considers only information extracted from minutiae, such as location, direction and type. It does not consider other information usually taken into account by fingerprint examiners, such as the general pattern of the ridge flow on the mark and the control prints. In this paper, we propose an improvement to our model that allows a fingerprint examiner to take advantage of pattern information when assessing the evidential weight to be assigned to a fingerprint comparison. We present an extension of the formal analysis proposed earlier and we illustrate our approach with an example.     

Calculating likelihood ratios for a mixed DNA profile when a contribution from a genetic relative of a suspect is proposed

This technical note describes a practical method for evaluating evidence in the case of a two person conditioned DNA mixture where the defence proposition is that the unknown contributor is genetically related to the suspect. A conditioned mixture is one where the presence of DNA from one of two individuals is accepted by both prosecution and defence. A typical example would be a vaginal swab in an alleged rape case, where the presence of the complainant's DNA would be expected and samples have been taken from the complainant and a suspect. Much has been written about the interpretation of such mixtures and the calculation of the conditional genotype probabilities that must be carried out. In general, such treatments assume that the unknown contributor, under the defence proposition, is unrelated to the known individuals. In this paper, we consider the case where the defence proposition is that the unknown contributor is genetically related to the suspect. We describe a method, incorporating a flow chart and reference tables that facilitate manual calculations of the likelihood ratio for several postulated genetic relationships.     

The interpretation of refractive index measurements V.

An approach to the interpretation of glass refractive index measurements in forensic science casework which has been developed in four previous papers is extended to deal with the calculation of coincidence probabilities in cases which involve multiple control and recovered samples. Examples of the calculations are given and there is a discussion of the possible limitations of the method.