Research paperSharing data on DNA transfer, persistence, prevalence and recovery: Arguments for harmonization and standardization
Introduction
The routine application of forensic DNAprofiling in criminal cases can lead to questions on the relevance of the traces that have been typed. Since being the donor of the DNA in a sample is not a crime, inferences regarding the relevance of the traces need to be made when DNA is used as evidence in a court case. These inferences lead us through the levels in the hierarchy of propositions [1]; from (sub-) source level (whose DNA or cell type is it?) to activity level (what activity led to deposition of the trace?) to offense level (can the activity be considered a criminal act?). To be able to address questions regarding the timing or activity that led to deposition of a biological trace (activity level inference), relevant information is needed on the probability of DNA transfer in various situations, its persistence over time given the environmental conditions and use of the object it is retrieved from, the general prevalence of DNA on objects/surfaces given their history, and the ability to recover and generate an informative DNA profile. The factors relevant in addressing the questions being raised are dependent on the case circumstances.
Within the field of forensic genetics there is growing awareness of the need for scientific data on transfer, persistence, prevalence and recovery (TPPR) of DNA (Table 1) under conditions relevant to criminal cases. This is reflected by an increasing number of publications dealing with these issues (Fig. 1). A similar trend is observed by Taylor et al. [2]. With the data available, and questions being put to the forensic practitioner by the courts, sharing current knowledge on these issues with judiciary is imperative [4].
It is crucial to assist the court in understanding the intricacies of DNA TPPR [4,5]. Sharing this information with the judiciary may take different forms. These could, for instance, be general answers (e.g. not case specific) to questions on factors to consider when interpreting test results. In other words, provide guidance to the factfinders in the case (judges or jury) when assessing the relevance of the findings in the case at hand. A formal probabilistic assessment of the evidence by the expert is the preferred way to address these issues [6,7]. To be able to perform such probabilistic assessments, data are needed from which probabilities of transfer, persistence, prevalence and/or recovery of DNA can be inferred.
Sharing data on these topics between laboratories and jurisdictions is relevant since similar types of cases are seen in many jurisdictions. Taylor et al. [2] list a number of commonly encountered issues surrounding TPPR of DNA and illustrate this with cases from a number of jurisdictions. From this we can infer that forensic practitioners in different jurisdictions may be confronted with the same questions on TPPR in similar cases. That these commonalities exist across jurisdictions is further illustrated by the publication of TPPR studies from different laboratories across the globe on similar issues. For instance, within a short time frame, four studies were published on (secondary) transfer of DNA to knife handles by laboratories from Australia [8] and UK and Australia [9], Switzerland [10] and the United States [11]. It is therefore conceivable that standardized sharing of data on TPPR may assist forensic experts in courtrooms across jurisdictions.
In the early nineties, European DNA scientists took an initiative that would ensure that common DNA typing systems would be used throughout the European Community [48,49]. The final objective of this initiative was to facilitate the criminal justice systems to exchange DNA typing data between different countries. To allow for the exchange of DNA profiling data between different countries, agreements had to be made between scientists on the selection of standard DNA systems. Ultimately, the way forward lay with the use of a European standard set of short tandem repeat (STR) loci [12]. Scientific results inclusive of inter-laboratory exercises between the forensic European laboratories have convinced scientists, legal professionals and legislators that reliable and robust DNA typing results can be obtained with the internationally selected core STR loci. These first initiatives have evolved into additional standard loci being adopted and becoming part of EU legislation [13], as well as in the establishment of a pan European DNA database where the data of 23 national DNA databases across the EU are shared [14]. This illustrates the importance of international collaboration and standardization in the forensic DNA community, and has set precedence for the harmonization of other areas within forensic genetics.
In this article we show that our knowledge on DNA transfer, persistence, prevalence and recovery issues can be vastly increased by similar strategies for harmonization and standardization. International collaboration and standardization in these fields will further enhance our scientific knowledge. The use of internationally endorsed standards in forensic investigations on DNA activity level issues will also have positive effects on the confidence from the legal community in this specific scientific field.
Here we will address the application of published data on TPPR to casework situations, demonstrating the impact on activity level assessments given differences in knowledge used and modes of its application. Based on this, we provide recommendations for sharing DNA TPPR data within the forensic DNA community. This paper will outline potential avenues to proceed, but does not provide a restrictive template for future work. We wish to start and fuel discussions on data sharing on TPPR issues, and suggest that international standardization and harmonization on these topics will benefit the forensic and legal communities as it has done in the past with STR typing.
Section snippets
The process of evaluating findings at the activity level
The way in which data from scientific literature is used to address questions at activity level in casework can depend on the forensic practitioner or laboratory. In this chapter we illustrate how forensic practitioners differ in their approach. We use a mock case example to illustrate the different approaches, and highlight current limitations that exist when using published data in casework. Suggestions to reduce these limitations are provided.
Standardization and harmonization
The ideal method to assign probabilities to DNA TPPR events would be to perform replicate experiments which are perfectly aligned with the known case circumstances. The experiments are performed using the exact same analysis and interpretation methods that were applied to the traces of interest. This approach would require substantial resources and would take a considerable amount of time for each case. As such, this ideal situation is unlikely to become commonplace due to restrictions in time
Towards a shared knowledge base
Currently, each scientist will explore scientific literature to find those studies that can be used to inform probabilities of TPPR. This can be quite labor-intensive, and relevant studies may be missed. Furthermore, these studies that are found may not present their data in a similar fashion, or could otherwise be limited in their use. A single ‘port-of-call’, for instance, a web-based portal, could assist forensic practitioners in finding relevant data. In this section we
outline a potential
Concluding remarks
There is a need to progress our collective pursuit to improve our addressing of DNA related activity level assessments. The proposed considerations in this article are presented as one set of possible enablers to assist in this endeavor. We hope that this paper will aid further discussion and trigger actions in the intended direction. Pending the availability of an online platform, we encourage authors to consider including a data supplement to their manuscripts. These data supplements could be
Funding
The project ‘DNActivity’ is part of the ENFSI project ‘Towards the Vision for European Forensic Science 2020 (TVEFS-2020)’ which is co-funded by the ‘Prevention of and Fight against Crime Programme of the European Union’ under agreement number HOME/2013/ISEC/MO/ENFSI/4000005962. This project has been funded with support from the European Commission. This publication reflects the views only of the authors, and the European Commission or any of the institutes hosting the authors cannot be held
Acknowledgements
We wish to express our gratitude to all forensic practitioners involved in the mock case exercise.
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