Understanding the variables impacting DNA transfer, persistence, prevalence and recovery (DNA-TPPR) has become increasingly relevant in investigations of criminal activities to provide opinion on how the DNA of a person of interest became present within the sample collected. This review considers our current knowledge regarding DNA-TPPR to assist casework investigations of criminal activities. There is a growing amount of information available on DNA-TPPR to inform the relative probabilities of the evidence given alternative scenarios relating to the presence or absence of DNA from a specific person in a collected sample of interest. This information should be used where relevant. However, far more research is still required to better understand the variables impacting DNA-TPPR and to generate more accurate probability estimates of generating particular types of profiles in more casework relevant situations. This review explores means of achieving this. It also notes the need for all those interacting with an item of interest to have an awareness of DNA transfer possibilities post criminal activity, to limit the risk of contamination or loss of DNA. Appropriately trained forensic practitioners are best placed to provide opinion and guidance on the interpretation of profiles at the activity level. However, those requested to provide expert opinion on DNA-related activity level issues are often insufficiently trained to do so. We advocate recognition of DNA activity associated expertise to be distinct from expertise associated with the identification of individuals. This is to be supported by dedicated training, competency testing, authorisation, and regular fit for purpose proficiency testing. The possibilities for experts to report on activity-related issues will increase as our knowledge increases through further research, access to relevant data is enhanced, and tools to assist interpretations are better exploited. Improvement opportunities will be achieved sooner, if more laboratories and agencies accept the need to invest in these aspects as well as the training of practitioners.

/pdf/dna-transfer-in-forensic-science-a-review-2shgt6g9kb.pdf

DNA transfer in forensic science: A review.

The use in courtrooms of forensic DNA typing results from presumably touched or handled items is increasing as the sensitivity of detection techniques improves. Research investigating how much DNA can be recovered from handled items, whether trace DNA can be detected under certain scenarios including varying degrees of indirect transfer, and factors which may influence these results is summarized here. Fundamentally, our current understanding of the cellular content of touch deposits and the origins of the potential trace DNA therein is extremely limited. Possible origins include anucleate corneocytes, fragmentary cells/nuclei, nucleated epithelial cells from hands, transferred nucleated cells, and cell-free DNA. Here we review the existing evidence for each possible source and consider remaining knowledge gaps regarding forensically relevant touch depositions.

/pdf/a-review-of-trace-touch-dna-deposits-variability-factors-and-2vxxoye5gb.pdf

A review of trace "Touch DNA" deposits: Variability factors and an exploration of cellular composition.

The value of the evidence depends critically on propositions. In the second of two papers intended to provide advice to the community on difficult aspects of evaluation and the formulation of propositions, we focus primarily on activity level propositions. This helps the court address the question of “How did an individual’s cell material get there?”. In order to do this, we expand the framework outlined in the first companion paper. First, it is important not to conflate results and propositions. Statements given activity level propositions aim to help address issues of indirect vs direct transfer, and the time of the activity, but it is important to avoid use of the word ‘transfer’ in propositions. This is because propositions are assessed by the Court, but DNA transfer is a factor that scientists need to take into account for the interpretation of their results. Suitable activity level propositions are ideally set before knowledge of the results and address issues like: X stabbed Y vs. an unknown person stabbed Y but X met Y the day before. The scientist assigns the probability of the evidence, if each of the alternate propositions is true, to derive a likelihood ratio. To do this, the scientist asks: a) “what are the expectations if each of the propositions is true?” b) “What data are available to assist in the evaluation of the results given the propositions?” When presenting evidence, scientists work within the hierarchy of propositions framework. The value of evidence calculated for a DNA profile cannot be carried over to higher levels in the hierarchy – the calculations given sub-source, source and activity level propositions are all separate. A number of examples are provided to illustrate the principles espoused, and the criteria that such assessments should meet. Ideally in order to assign probabilities, the analyst should have/collect data that are relevant to the case in question. These data must be relevant to the case at hand and we encourage further research and collection of data to form knowledge bases. Bayesian Networks are extremely useful to help us think about a problem, because they force us to consider all relevant possibilities in a logical way. An example is provided.

DNA commission of the International society for forensic genetics: Assessing the value of forensic biological evidence - Guidelines highlighting the importance of propositions. Part II: Evaluation of biological traces considering activity level propositions.

Since DNA from touched items and surfaces ("touch DNA") can successfully and reliably be analyzed, the question as to how a particular DNA containing sample came to be from where it was recovered is of increasing forensic interest and expert witnesses in court are increasingly challenged to assess for instance whether an incriminatory DNA sample matching to a suspect could have been transferred to the crime scene in an innocent manner and to guess at the probability of such an occurrence. The latter however will frequently entail expressing a subjective probability i.e. simply making a best guess from experience. There is, to the present date, an extensive and complex body of literature on primary, secondary, tertiary and even higher order DNA transfer, its possibility, plausibility, dependency on an array of variables and factors and vast numbers of permutations thereof. However, from our point of view there is a lack of systematic data on DNA transfer with existing research widely varying in quality and relevance. Our aim was, starting from a comprehensive survey of the status quo and appreciating its increasing importance, to in the first part of our review raise consciousness towards the underestimated and insufficiently accounted for complexity of DNA transfer and thus appendant research of forensic scientists serving as expert witnesses in court but also acting in the role of a journal referee to point them to areas of criticism when reviewing a manuscript on DNA transfer. In the second part, we present propositions how to systematize and integrate future research efforts concerning DNA transfer. Also, we present a searchable database providing an extensive overview of the current state of knowledge on DNA transfer, intended to facilitate the identification of relevant studies adding knowledge to a specific question and thus help forensic experts to base their opinion on a broader, more complete and more reproducible selection of studies.

On DNA transfer: The lack and difficulty of systematic research and how to do it better.

Among the various items recovered from crime scenes or persons involved in a crime event, clothing items are commonly encountered and submitted for forensic DNA sampling. Depending on the case circumstances and the activity-of-interest, sampling of the garment may concentrate on collecting DNA from the wearer, or from one or more offenders who have allegedly contacted the item and/or wearer. Relative to the targeted DNA, background DNA already residing on the item from previous contacts, or transferred during or after the crime event, may also be collected during sampling and observed in the resultant DNA profile. Given our limited understanding of how, and from where, background DNA is derived on clothing, research on the transfer, persistence, prevalence, and recovery (TPPR) of DNA traces from upper garments was conducted by four laboratories. Samples were collected from several areas of two garments, each worn on separate working or non-working days and individually owned by four individuals from each of the four laboratories, and processed from DNA extraction through to profiling. Questionnaires documented activities relating to the garment prior to and during wearing, and reference profiles were obtained from the wearer and their close associates identified in the questionnaire. Among the 448 profiles generated, variation in the DNA quantity, composition of the profiles, and inclusion/exclusion of the wearer and their close associates was observed among the collaborating laboratories, participants, garments worn on different occasions, and garment areas sampled.

Assessment of the transfer, persistence, prevalence and recovery of DNA traces from clothing: An inter-laboratory study on worn upper garments

Despite a broad consensus that cycling can address a range of transportation issues, many countries have struggled to institute measures to increase cycling participation. Even for cities that have achieved marked progress, there remains a gap in making cycling a truly normative mode of transportation. The practical problem of translating research and converting policy vision into broad-based cycling participation has become an increasingly central focus of international cycling scholarship. To examine the challenges of practically planning for cycling, we focus on the role of local government and report on a survey of all urban and major regional local governments in Australia and New Zealand. By analyzing results across the two countries, we diagnose challenges faced by practitioners in implementing measures to support cycling. Key findings suggest there is support among local government officers and stakeholders for cycling to play an increased role in daily transportation, yet this support is much more mixed at the implementation stage of cycling plans, policies, and infrastructure projects. These findings indicate a pressing need to better equip local government practitioners with tools and knowledge to overcome barriers to providing for cycling, particularly in increasingly politicized and complex contexts.

Planning for cycling in local government: Insights from national surveys in Australia and New Zealand

During an investigation, the question of interest might be whether or not a person has worn a given garment. Wearer DNA studies have contributed to our knowledge and understanding of DNA transfer and persistence on items of worn clothing. However, there is currently no extensive dataset on DNA profiling outcomes from a variety of upper garments. Therefore we investigated the DNA profiling outcomes from the collars and/or cuffs of forty-four upper garments of worn clothing and determined the quantity of wearer and non-wearer DNA recovered. Interpretable DNA profiles were more likely to be obtained from collars than cuffs (84% versus 71%). The wearer was detected in all interpretable profiles and a major profile corresponding to the wearer was the most common outcome from both collar and cuff samples (48% and 50%, respectively). There was large variation in the amount of wearer DNA recovered and the average recovered was approximately 20 ng. Usually more wearer DNA was found on collars than cuffs of the same garment and, on average, more non-wearer DNA was found on cuffs than collars. No DNA was recovered from the cuffs of two garments despite these garments being worn for three and four hours, respectively. On one occasion a non-wearer contributed more DNA to a cuff sample than the wearer. We found no correlation between wearing time and the amount of wearer DNA recovered which indicates that other factors (e.g. shedder status and/or the manner of contact between the garment and skin) have a greater influence, than wearing time, on the amount of DNA transferred. However, there was a positive correlation between wearing time and the likelihood of obtaining interpretable profiles. This work has generated data to support the evaluation of DNA evidence from clothing and we provide a case example to demonstrate this.

Wearer and non-wearer DNA on the collars and cuffs of upper garments of worn clothing

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Planning for cycling in local government: Insights from national surveys in Australia and New Zealand

Wearer and non-wearer DNA on the collars and cuffs of upper garments of worn clothing