Opportunistic crimes: Evaluation of DNA from regularly-used knives after a brief use by a different person

© 2019 Elsevier B.V. When evaluating trace DNA recovered from evidential items in forensic casework, it is crucial to consider how the DNA got there, and such evaluative interpretations should ideally be informed by published experimental data. A key activity-level question is whether the DNA obtained comes from the regular user, the last user (ostensibly the user at the time of the crime) or from indirect transfer events. The aim of this experiment was to provide data to contribute to answering this question, particularly when considering opportunistic crimes, in which an offender might grab the nearest item at hand required for their purpose, e.g. a weapon or tool, and therefore only handle it very briefly. Volunteers (‘regular users’) used knives in a prescribed manner to simulate regular use (one user per knife); DNA recovery by mini-tapes from these knives gave ˜1–10 ng DNA, with <16% non-donor DNA from indirect transfer events. Different volunteers (‘second users’) then stabbed replicate sets of regularly-used knives into a foam block for either 2, 30 or 60 s (on different occasions), with each timeframe in triplicate, and DNA was recovered from the knife handles using mini-tapes. For knives regularly-used by three of the four volunteers, the ratios of regular user to second user DNA were approximately 4:1, 2:1 and 1:1 for durations of use by the second user of 2, 30 and 60 s, respectively. Analysis of the respective quantities of DNA showed that this trend resulted from a decrease in regular user DNA via transfer to the second user's hands, rather than an increase in DNA deposition from the second user. However, for knives regularly-used by the fourth volunteer, DNA from the regular user remained at significantly higher quantities than DNA from the second user and unknown sources, irrespective of duration of use by the second user. Furthermore, one volunteer deposited a similar amount of DNA through regular use as the amount of indirectly-transferred unknown DNA deposited by another volunteer's hands. These observations indicate that caution should be taken when relying solely on absolute quantities of DNA to inform evaluative interpretations, and other parameters, such as profile quality and relative contributions to mixed profiles, should also be taken into account. To better assist activity level assessments, more extensive studies of this manner should be conducted to obtain probability distributions of different types of profiles resulting from this kind of activity

DNA transfer in forensic science: A review

© 2018 Elsevier B.V. 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

DNA Transfer in Forensic Science: Recent Progress towards Meeting Challenges.

Understanding the factors that may impact the transfer, persistence, prevalence and recovery of DNA (DNA-TPPR), and the availability of data to assign probabilities to DNA quantities and profile types being obtained given particular scenarios and circumstances, is paramount when performing, and giving guidance on, evaluations of DNA findings given activity level propositions (activity level evaluations). In late 2018 and early 2019, three major reviews were published on aspects of DNA-TPPR, with each advocating the need for further research and other actions to support the conduct of DNA-related activity level evaluations. Here, we look at how challenges are being met, primarily by providing a synopsis of DNA-TPPR-related articles published since the conduct of these reviews and briefly exploring some of the actions taken by industry stakeholders towards addressing identified gaps. Much has been carried out in recent years, and efforts continue, to meet the challenges to continually improve the capacity of forensic experts to provide the guidance sought by the judiciary with respect to the transfer of DNA

Trace DNA evidence dynamics: An investigation into the deposition and persistence of directly- and indirectly-transferred DNA on regularly-used knives

Empirical data on the transfer and persistence of trace DNA are crucial to the evaluation of forensic DNA evidence. This evaluation can be complicated by the occurrence of indirect DNA transfer; the possibility of which is well established, but research into such transfer is often focussed on unrealistic situations, e.g. handling of DNA-free items after participants have shaken hands for 1–2 min. To simulate more realistic scenarios, this study investigated the deposition and persistence of both directly- and indirectly-transferred DNA on knives that had been artificially set up as ‘regularly-used’. Each knife was handled in a prescribed manner by a specific participant over two consecutive days to simulate regular use. Each participant then shook hands for 10 s with a fellow volunteer and immediately stabbed one of their knives into a foam block repeatedly for 60 s. DNA was recovered by mini-taping from triplicate sets of knife handles from four pairings of volunteers after regular use, and at one hour, one day and one week after the handshaking and stabbing events. Total amounts of DNA recovered from the knives, regularly used by a single person, varied among individuals; one volunteer consistently deposited significantly greater amounts than the others, whilst another volunteer did not always leave complete profiles. DNA attributed to the regular user persisted for at least a week, declining with increasing time between DNA deposition and recovery. Non-donor DNA was co-deposited at <5% of the profiles recovered, except for one volunteer, who consistently left DNA from their romantic partner on their knives at ∼25% and ∼11% of the profiles before and after the handshaking and stabbing events, respectively. In three pairings of volunteers, after the handshaking and stabbing events, alleles that could be attributed to the respective handshakers’ profiles were detected as partial minor profiles, equating to ∼10% of the profiles recovered. For the fourth pairing of volunteers, only complete single-source DNA profiles matching the regular user’s profile were recovered. However, it is important to note that, when indirectly-transferred handshaker DNA was detected, it declined with increasing time between DNA deposition and recovery. These data provide an initial insight into the detection and persistence of directly- and indirectly-transferred DNA that extend the data already available on forensic DNA transfer. The results herein suggest that the sooner an item is sampled after an offence has occurred, the greater the chance of recovering indirectly-transferred DNA, which has implications for forensic reconstructions

The effects of soaking for DNA recovery on the striation patterns of fired cartridge cases

© 2019, © 2019 Australian Academy of Forensic Sciences. The recovery of trace DNA from fired cartridge cases has recently gained increased interest throughout the literature, with a variety of methods currently being explored. Soaking fired cartridge cases in a lysis buffer holds potential in producing meaningful DNA profiles; however, chemical interactions between the lysis buffer and brass cartridge cases may limit the efficacy of this method. This preliminary study examines the effects of soaking on the microscopic striation detail of brass and nickel 9 mm Parabellum (9 mmP) calibre and.22 Long Rifle (.22LR) calibre fired cartridge cases. Headstamp and coarse striation patterns on 9 mmP fired cartridge cases and finer striation patterns along the outer wall of.22LR fired cartridge cases were microscopically examined prior to and following soaking. Soaking was performed by submerging the fired cartridge cases in 380 µl of ATL buffer (Qiagen, Germany) for 20 minutes. Microscopic analysis of brass and nickel 9 mmP and.22LR fired cartridge cases showed that coarse and fine striation detail remain unaffected following soaking. These results indicate that comparative ballistics examinations may be performed following DNA recovery using the soaking method

Evaluation of soaking to recover trace DNA from fired cartridge cases

© 2020, © 2020 Australian Academy of Forensic Sciences. The recovery of trace DNA from cartridge cases is of common interest across many jurisdictions. Soaking offers improved profiling success rates over traditional methods. We evaluated the effects of firing, calibre, and metal composition on controlled and handled DNA samples utilizing a soaking method. Our results show that firing decreases the quantities of DNA recoverable from cartridge cases and higher quantities of DNA are recoverable from nickel ammunition compared to brass. In spiked samples, calibre of ammunition had no significant effect on DNA recovery. Despite slight to moderate DNA degradation and variable profiling success rates, spiked unfired and fired nickel cartridges resulted in more usable profiles than brass cartridges. These findings can aid in triaging the types of ammunition subjected to DNA testing

Trace DNA analysis: Do you know what your neighbour is doing?. A multi-jurisdictional survey

Since 1997 the analysis of DNA recovered from handled objects, or 'trace' DNA, has become routine and is frequently demanded from crime scene examinations. However, this analysis often produces unpredictable results. The factors affecting the recovery of full profiles are numerous, and include varying methods of collection and analysis. Communication between forensic laboratories in Australia and New Zealand has been limited in the past, due in some part to sheer distance. Because of its relatively small population and low number of forensic jurisdictions this region is in an excellent position to provide a collective approach. However, the protocols, training methods and research of each jurisdiction had not been widely exchanged. A survey was developed to benchmark the current practices involved in trace DNA analysis, aiming to provide information for training programs and research directions, and to identify factors contributing to the success or failure of the analysis. The survey was divided in to three target groups: crime scene officers, DNA laboratory scientists, and managers of these staff. In late 2004 surveys were sent to forensic organisations in every Australian jurisdiction and New Zealand. A total of 169 completed surveys were received with a return rate of 54%. Information was collated regarding sampling, extraction, amplification and analysis methods, contamination prevention, samples collected, success rates, personnel training and education, and concurrent fingerprinting. The data from the survey responses provided an insight into aspects of trace DNA analysis, from crime scene to interpretation and management. Several concerning factors arose from the survey. Results collation is a significant issue being identified as poor and differing widely, preventing inter-jurisdictional comparison and intra-jurisdictional assessment of both the processes and outputs. A second point of note is the widespread lack of refresher training and proficiency testing, with no set standard for initial training courses. A common theme to these and other issues was the need for a collective approach to training and methodology in trace DNA analysis. Trace DNA is a small fraction of the evidence available in current investigations, and parallels to these results and problems will no doubt be found in other forensic disciplines internationally. The significant point to be realised from this study is the need for effective communication lines between forensic organisations to ensure that best practice is followed, ideally with a cohesive pan-jurisdictional approach. Crown Copyright © 2007