A Logical Framework for Forensic DNA Interpretation

Driver or passenger? Use of a Bayesian network for the evaluation of DNA results in a fatal car accident

This article presents a case where the issue was to determine who was the driver and who was the passenger at the time of a fatal car accident involving two persons, one of whom died in the accident. The presence of the two persons in the car was not contested, only the mechanisms that led to the deposition of the DNA (i.e., the activities) were. To our knowledge, few cases are evaluated considering the alleged activities. The reasons for this include the lack of knowledge, and data, as well as the difficulties encountered for the formulation of conclusions. In this case report, we present the architecture of the Bayesian Network (BN) used to evaluate the DNA results of the traces recovered from the steering wheel, driver's and passenger's airbags. The following propositions were considered: "The person of interest (POI) was driving the car and the alternative person (AP) was the passenger at the time of the accident" or vice versa. We discuss the assumptions that were made and how data from the literature was used to parametrize into the BN. A likelihood ratio of the order of 90 was finally assigned. The statement proposed to the mandating authority indicated that, given the information that was made available to us, our observations were of the order of 90 times more probable if the POI was driving the car at the time of the accident rather than if the AP was. A sensitivity analysis was performed (5000 simulations): this shows that our likelihood ratio is robust.

From frequented environments to the crime scene: Evaluating findings of fibre comparisons in complex transfer scenarios

The evaluation of the results from a fibre comparison given activity level propositions is well established when considering only a single group of potential primary transfers. However, secondary transfers are less prevalent in the literature despite their potential value, especially in cases where the primary transfers are not sufficiently informative. In particular, one can consider the fibres from frequented environments of the person of interest (POI) identified in a struggle. If the POI did struggle with the complainant, these fibres can potentially be recovered in small quantities on the surface of the complainant as a result of secondary or higher order transfers. Therefore, these fibres may provide useful information that can resolve competing propositions involving struggles, as well as forensic intelligence in the form of linkages or investigative leads. If a non-differentiation is indeed found between recovered fibres and fibres from the frequented environments of the POI, these results need to be properly interpreted. In this paper, a model, based on an object oriented Bayesian network (OOBN), for evaluating such findings along with its implementation is proposed. Using available data from the literature and other sources, the model was then used to assess a few hypothetical scenarios involving secondary transfers. The results provided useful insights into secondary transfer that help to validate the model and demonstrate the potential utility that can be gained by considering transfers beyond the primary order. Moreover, these results can be used to help guide future research by identifying gaps in the literature. Finally, the direct application to a case study was conducted to demonstrate the practical aspects of such a model.

Global survey on evaluative reporting on DNA evidence with regard to activity-level propositions

For many criminal cases, the source of who deposited the DNA is not what the prosecutor and the defense are trying to dispute. In court, the question may be how the DNA was deposited at the crime scene rather than who the DNA came from. Although laboratories in many countries have begun to evaluate DNA evidence given formal activity-level propositions (ALPs), it is unknown how much other forensic practitioners know and what they think about activity-level evaluative reporting (ALR). To collect this information, a survey with 21 questions was submitted to international forensic science organizations across Europe, Australia, South America, Canada, Asia, and Africa. The survey combined open-ended and multiple-choice questions and received 162 responses. Responses revealed a wide range of knowledge on the topic. Overall, most respondents were somewhat knowledgeable about ALR, ALP, and current practices in court and expressed their support of the concept. A majority of participants identified gaps and obstacles regarding ALR they would like to see addressed. Examples include (1) need for more education/training at all stakeholder levels, (2) need for more DNA evidence-related data under realistic case scenarios, (3) need to internally implement and validate a formalized and objective approach for reporting, and (4) in some countries the need to achieve court admissibility. This global survey gathered the current concerns of forensic DNA practitioners and outlined several operational concerns. The information can be used to advance the implementation of ALR in laboratories and court testimony worldwide.

A study of DNA transfers onto plastic packets placed in personal bags

The ability to detect low level DNA brings with it the uncertainty of whether the detected DNA is a result of transfer. To address this uncertainty, a simulation study was conducted in which a mock illicit drug packet was placed into the personal bags of individuals. When the average transit time of the packets was increased from around 2 h to more than 14 h, the percentage of the DNA profiles recovered from the packets which could be attributed to the individuals increased greatly from 5.3% to 48.6%. We found that drug packers who were poor shedders could not be included as contributors to the DNA profiles from the drug packets at all and there was a higher chance that individuals other than themselves could be included as contributors to the DNA profile recovered from drug packets. We also found that it was equally likely that the drug packers who had direct contact with the drug packets and bag owners who did not, could be included as contributors to the DNA profiles recovered from the packets. The results in this study highlight the importance of taking into consideration the transit time of drug packet, the shedder status of the alleged packer and the history of an item, when evaluating DNA evidence in the context of illicit drug activities.

DNA transfer when using gloves in burglary simulations

Several studies have demonstrated that DNA can be indirectly transferred from an individual onto a surface. Therefore, the presence of DNA that is compatible with a given person does not necessarily mean that this person has touched the surface on which the DNA was recovered. The present work simulates cases, where DNA is recovered on a door handle and compared to several reference DNA profiles. The DNA profile of the trace shares DNA components with a person of interest (POI). When asked about the DNA results, the POI says he has nothing to do with the incident and has never been at the scene. However, a possibility would be that the DNA came from his recently stolen gloves. Someone else, the alternative offender (AO), could have opened the door wearing his gloves (POI's gloves), and transferred his DNA (POI's DNA). Based on the above-mentioned scenario, 60 burglary simulations experiments were carried out to generate data to assess DNA results given these allegations. The quantity and quality of DNA profiles (NGM SElect) recovered when the POI opened/closed the door bare-handed or when someone else performed the same activity but using POI's gloves, were compared. The gloves were regularly worn during at least three months by their owner during the winter. On the contrary, the AO wore them only for two minutes. Among the traces collected on the door handles, less than 50% of the traces led to interpretable DNA profiles. In 30% of the cases (3/10), when the door was opened/closed with bare hands, the DNA found on the door handle led to a mixed DNA profile with the POI's DNA aligning with the major contributor. For the experiments where the AO opened/closed the door with the POI's gloves, the POI's DNA was compatible with 22% (11/50) of the mixed DNA profile, aligning with the major in 8% of the cases (4/50). The DNA profiles of the offices' occupants were observed on the door handles, but not the AO's. In addition to the results of the experiments, we show two examples of how one can assess results observed in casework. Given the possibility of indirect transfer of minute DNA quantities, this research emphasizes the need to evaluate DNA results given the activities when the POI has a legitimate reason that can explain the presence of their DNA.

Reporting on forensic biology findings given activity level issues in the Netherlands

There appears to be some hesitation within the forensic biology community to formally evaluate and report on findings given activity level propositions. This hesitance in part stems from concerns about the lack of relevant data on the dynamics of biological traces and doubt about the relevance of such expert opinions to the trier of fact. At the Netherlands Forensic Institute formal evaluative opinions on the probability of case findings given propositions at the activity level are provided since 2013, if requested by a mandating authority. In this study we share the results from a retrospective analysis of 74 of such requests. We explore which party initiates requests, the types of cases that are submitted, the sources of data being used to assign probabilities to DNA transfer, persistence, prevalence and recovery (TPPR) events, the conclusions that were drawn by the scientists, and how the conclusions were used by the courts. This retrospective analysis of cases demonstrates that published sources of data are generally available and can be used to address DNA TPPR events in most cases, although significant gaps still remain. The study furthermore shows that reporting on forensic biology findings given activity level propositions has been generally accepted by the district and appeal courts, as well as the other parties in the criminal justice system in the Netherlands.

Integrity, Trustworthiness, and Effectiveness: Towards an Ethos for Forensic Genetics

Forensic genetics comes under critical scrutiny when developments challenge previously accepted legal, ethical, social, and other boundaries. Forensic geneticists continue to build a knowledge culture within a community of practice that acknowledges ethical standards of conduct in both research and the societal application of forensic genetics. As the community further cements and extends its societal role, and in that process often pushing at ethical and legal boundaries, it requires a strong, resilient, and responsive ethos that, in setting clear parameters for conduct, fosters the field's sense of purpose. While supra-national declarations and human rights protections, coupled with local regulations, provide some parameters for practice, and discipline-specific guidance has refined an agenda for forensic genetics research and application, this maturing field needs to now define its core principles. This contribution proposes the values of integrity, trustworthiness, and effectiveness as a foundational triptych for a bespoke forensic genetics ethos to ensure the augmentation of developments that range from a purely science-oriented to a wider societally relevant knowledge culture.