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The heightened sensitivity of DNA typing techniques, paired with the extensive use of trace DNA in forensic investigations, has resulted in an increased need to understand how and when DNA is deposited on surfaces of interest. This study focussed on the transfer, persistence, and prevalence of trace DNA in a single occupation of an office space by an intruder, when all contacts made during occupation and for the two hours prior and post occupation were known. The extent to which DNA could be recovered from contacted/not contacted surfaces was investigated. This study investigates the impacts of these movements and use of an office space when the duration of occupancy, surface contact histories and shedder status of participants are known. Contacts were documented and surfaces in the office space were targeted for sampling. Categories were set for target sampling that included different types of contact. Direct and indirect DNA transfer was detected in 55 % and 6 % of samples, respectively. Contactless DNA transfer was detected in 0.5 % of samples. The owner was observed as the sole/major/majority contributor in 77 % of the samples and as minor contributor in 10 % of samples. The intruder was observed as the sole/major/majority contributor in 14 % of samples and as the minor contributor in 16 %. An increased number of contacts increased the relative DNA contribution of the individual making the contact, however, not all observed direct contacts resulted in detectable DNA transfer. The outcome of this study will aid in better sample targeting strategies and contribute to the pool of data assisting in the development of activity level assessments., Competing Interests: Declaration of Competing Interest The authors declare no competing interests., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

According to the principle of Locard "Every contact leaves a trace", when touching a surface, a bi-directional transfer of self and non-self-DNA residing on the hands and touched objects can occur. Metals are commonly encountered in forensic evidence and, during hand contact with these surfaces, a transfer of metal particles could occur together with the transfer of human DNA. This study proposes a proof-concept approach for the original detection of metal particles and touch DNA to track the activity performed by a donor and particularly to assess the metallic substrate touched before the contact with a subsequent surface. To this scope, a scenario of contact events was simulated by three volunteers, who participated in fingerprint deposition firstly on copper and then on plastic and glass surfaces. Twenty-four stubs were collected on the hands of volunteers and the secondary surfaces and then analyzed by environmental scanning electron microscopy (ESEM). DNA was quantified only from copper and plastic surfaces. Ten additional volunteers followed the same protocol of deposition on copper and then on plastic surfaces to evaluate DNA transfer only. On 20 touch DNA samples, the copper surface yielded significantly lower DNA amounts, ranging from 0.001 to 0.129 ng/μl, compared to the secondary touched plastic surface, ranging from 0.007 to 0.362 ng/μl. ESEM-EDS analysis showed that copper particles could be abundantly detected on the hands of the volunteers after contact with the copper surface. Particles containing silicates with copper were shown on plastic, while they were only found in 1/3 of samples on glass. Our proof-of-concept study has shown that ESEM-EDS analysis has the potential to detect copper particles transferred to the hands of volunteers during contact with a copper metallic surface and deposited on secondarily touched items. The results suggest that this original ESEM-DNA parallel approach could potentially allow the tracking of DNA transfer and metal particles at a crime scene, although this represents only a first step and further research on a wider casuistry could help to address the interpretation of results given activity level propositions., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Considering activity level propositions in the evaluation of forensic biology findings is becoming more common place. There are increasing numbers of publications demonstrating different transfer mechanisms that can occur under a variety of circumstances. Some of these publications have shown the possibility of DNA transfer from site to site on an exhibit, for instance as a result of packaging and transport. If such a possibility exists, and the case circumstances are such that the area on an exhibit where DNA is present or absent is an observation that is an important diagnostic characteristic given the propositions, then site to site transfer should be taken into account during the evaluation of observations. In this work we demonstrate the ways in which site to site transfer can be built into Bayesian networks when carrying out activity level evaluations of forensic biology findings. We explore the effects of considering qualitative vs quantitative categorisation of DNA results. We also show the importance of taking into account multiple individual's DNA being transferred (such as unknown or wearer DNA), even if the main focus of the evaluation is the activity of one individual., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

The sensitivity of DNA analysis has progressed to the point that trace levels of DNA, originating from only a few cells, can generate informative profiles. This means that virtually any item or surface can be sampled with a reasonable chance of obtaining a DNA profile. As the presence of DNA does not suggest how it was deposited, questions are often raised as to how the DNA came to be at a particular location and the activity that led to its deposition. Therefore, understanding different modes of DNA deposition, reflective of realistic forensic casework situations, is critical for proper evaluation of DNA results in court. This study aimed to follow the movements of DNA to and from individuals and common household surfaces in a residential premises, while socially interacting. This took place over an hour and involved four participants, with known shedder status, designated as visitors (a male and a female) and hosts (a male and a female), who engaged in the activity of playing a board game while being served food. During the study, the participants were instructed to use the toilet on a single occasion to assess the transfer of DNA to new and unused underwear that was provided. All contacts made by the participants in the dining room and kitchen were video recorded to follow the movements of DNA. Samples were collected based on the history of contact, which included hands, fingernails and penile swabs. Direct contacts resulted in detectable transfer (LR > 1) in 87 % (87/100) of the non-intimate samples and clothing. For surfaces touched by multiple participants, DNA from the person who made the last contact was not always detectable. The duration and number of contacts did not significantly affect the detection of the person contacting the item. On the other hand, presence of background DNA and participant's shedder status appear to play an important role. Further, unknown contributors were detected in the majority of samples. Finally, indirect transfer was observed on a number of occasions including co-habiting partners of guests who were not present at the study location. The results of this study may assist with decision making for exhibit selection or targeting areas for sampling within the home environment. Our findings can also be used in conjunction with previous literature to develop activity-level evaluations in such situations where the source of the DNA is conceded, but the mode of deposition is disputed., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

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., Competing Interests: Declaration of Competing Interest No conflict of interest., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

The development of increasingly efficient DNA extraction and profiling kits has increased the amount of allelic information obtained from trace DNA samples, but also inadvertently, increased the detection of DNA contamination. This study aimed to evaluate the potential of DNA transfer using fluorescein, fluorescent under an alternate light source, in the use of a range of forensically relevant DNA profiling consumables. An evaluation of two pre-lysis methods adopting three different sample tubes, some with deliberate seal damage, showed the PrepFiler™ Automated Forensic DNA Extraction Kit caused leakage and crusting when the rim of the PrepFiler™ LySep column was compromised, but no leakage was observed under the same conditions using the Investigator STAR Lyse&Prep kit. The AutoLys tube showed minimal leakage using the PrepFiler™ chemistry. A DNA extract tube with an external thread, similar to the AutoLys tube, showed no leakage after fridge or freezer storage. However, it highlighted that a centrifugal spin does not guarantee all the DNA will pool at the base of the tube. A comparison of adhesive plate sealing films to 8-well strip caps for sealing 96-well PCR plates showed the adhesive plate sealing films presented a lower risk of DNA transfer, largely due to the adhesion of dispersed liquid on the sticky surface of the film. Overall, this study highlighted a number of variables that may be considered in the development of more refined contamination minimisation protocols in respect to increased sensitivities of DNA profiling., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Crown Copyright © 2024. Published by Elsevier B.V. All rights reserved.)

Domestic animals, such as cats and dogs, are present in the majority of Australian households. Recently, questions regarding the possibility that domestic animals can serve as silent witnesses, from whom evidence can be collected, or act as vectors of contamination and transfer, have started to be raised. Yet, little is known regarding the transfer and prevalence of human DNA to and from cats. This study investigated if cats are reservoirs and vectors for human DNA transfer. Twenty cats from 15 households were sampled from 4 different areas (head (fur), back (fur), left (skin) and right (fur)) to obtain information on the background DNA that may be found on an animal. Further, transfer of human DNA to and from an animal, after a short patting contact, was tested. Human DNA was found to be prevalent on all cats. Of the areas sampled, most DNA was collected from the top of the fur from the back followed by the head and right/fur. No or very low quantities of human DNA was recovered from the left (skin) area. Most of the human DNA originated from the owners, but DNA from others was also often present (47 % of samples). Further, the transfer tests demonstrated that human DNA transferred readily to (detected in 45 % of samples) and from (detected in 80 % of samples) cats during patting. These results show that animals can act as reservoirs of human DNA and vectors for human DNA transfer that may need to be considered during evaluative DNA reporting. Furthermore, if an interaction between an animal and a perpetrator is suspected, consideration should be given to collecting DNA evidence from suspected contact areas on an animal., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Individuals leave behind traces of their DNA wherever they go. DNA can be transferred to surfaces and items upon touch, can be released into the air, and may be deposited in indoor dust. The mere presence of individuals in a location is sufficient to facilitate either direct or indirect DNA transfer into the surrounding environment. In this study, we analyzed samples recovered from commonly touched surfaces such as light switches and door handles in an office environment. We evaluated two different methods to isolate DNA and co-extract DNA and RNA from the samples. DNA profiles were compared to the references of the inhabitants of the different locations and were analyzed taking into consideration the type of sampled surface, sampling location and information about the activities in a room during the sampling day. Results from DNA samples collected from surfaces were also compared to those from air and dust samples collected in parallel from the same areas. We characterized the amount and composition of DNA found on various surfaces and showed that surface DNA sampling can be used to detect occupants of a location. The results also indicate that combining information from environmental samples collected from different DNA sources can improve our understanding of DNA transfer events in an indoor setting. This study further demonstrates the potential of human environmental DNA as an investigative tool in forensic genetics., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Shedder status is defined as the propensity of an individual to leave DNA behind on touched items or surfaces and has been suggested as one of the major factors influencing DNA transfer. However, little is known about whether shedder status is a constant property of an individual across multiple measurements or when the environmental conditions are changed. We have assessed DNA depositions of six males on 20 occasions to acquire a reference data set and to classify the participants into high, intermediate, or low shedders. This data set was also used to investigate how the probability of a correct shedder status classification changed when the number of DNA deposition measurements increased. Individual sweat rates were measured with a VapoMeter and data regarding hygiene routines were collected through a questionnaire on each sampling occasion. Next, we investigated how changes in the experimental conditions such as seasonal variation, hygiene routines, the temperature of the touched object, and repeated handling of an object influenced the DNA shedding. Additionally, we assessed DNA collected from the face and from T-shirts worn by the six participants to explore whether shedder status may be associated with the relative amount of DNA obtained from other body parts. Our results indicate that shedder status is a stable property across different seasons and different temperatures of handled objects. The relative DNA amounts obtained from repeatedly handled tubes, worn T-shirts, and from faces reflected the shedder status of the participants. We suggest that an individual's shedder status is highly influenced by the DNA levels on other body parts than hands, accumulating on the palms by frequently touching e.g., the face or previously handled items harboring self-DNA. Assessing physiological differences between the participants revealed that there were no associations between DNA shedding and individual sweat rates., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

When sampling an item or surface for DNA originating from an action of interest, one is likely to collect DNA unrelated to the action of interest (background DNA). While adding to the complexity of a generated DNA profile, background DNA has been shown to aid in resolving the genotypes of contributors in a targeted sample, and where references of donors to the background DNA are not available, strengthen the LR supporting a person of interest contributing to the targeted sample. This is possible thanks to advances in probabilistic genotyping, where forensic labs are able to deconvolute complex DNA profiles to obtain lists of genotypes and their associated weights. Coupled with DBLR™, one can then compare multiple evidentiary profiles to each other to determine the contribution of common, but unknown, contributors. Here, we consider factors associated with taking background samples and whether one should collect multiple background samples that all relate to a single target sample, or if one should collect larger background samples rather than smaller samples. Background samples consisted of DNA accumulated on the items primarily by one or both occupants of a single household, while targeted samples were generated from touch deposits, or saliva deposits that had been left to air dry. Samples were collected from areas of various sizes, consisting of only the background, the target and the background directly beneath it, and the target and additional surrounding background. A broad range of DNA quantities were recovered, with larger background samples (400 cm 2 ) yielding significantly more DNA than smaller background samples (30 cm 2 ). Significant differences in DNA quantities between target samples were not observed. Generated DNA profiles were interpreted using STRmix™ and DBLR™, and where there was support for a common donor between the background and target sample, pairwise comparisons were performed to observe the effect on the LR supporting the target DNA donor contributing to the targeted sample when conditioning on one (or two) common donor between the targeted sample and 1-8 background samples. Multiple background samples gave significantly higher LRs compared to a single background sample, the larger sampled background area resulted in larger LR gains than the smaller areas, and four or more background samples reduced LR variability considerably. Here we provide recommendations for the minimum and ideal number of additional background samples that should be collected, and that several smaller samples may be more beneficial than a single larger sample., Competing Interests: Declaration of Competing Interest The authors declare that they have no conflict of interest., (Copyright © 2023 Elsevier B.V. All rights reserved.)

DNA unrelated to an action of interest (background DNA) is routinely collected when sampling an area for DNA that may have originated from an action of interest. Background DNA can add to the complexity of a recovered DNA profile and could impact the discrimination power when comparing it to the reference profile of a person of interest. Recent advances in probabilistic genotyping and the development of new tools, now allow for the comparison of multiple evidentiary profiles to query for a common DNA donor. Here, we explore the additional discrimination power that can be gained by having an awareness of the background DNA present on a surface prior to the deposition of target DNA. Samples with varying number of contributors and DNA quantities were generated on cleaned plastic pipes (where ground truth was known) and items used by occupants of a single household (where ground truth was not known). The background consisted of deposits made by hands (touch) while target deposits were both touch and saliva. Samples were collected from areas consisting of only the background (A), the target and the background directly beneath it (B), and the target and additional surrounding background (B+C). Samples B and B+C yielded similar DNA amounts when the target consisted of saliva, but when the target consisted of touch, significantly more DNA was recovered from B+C. Subsequently generated DNA profiles were interpreted using STRmix™ and DBLR™. The first approach involved no conditioning while the second approach involved conditioning on the reference profiles of the known background DNA donors. The third approach involved conditioning on one common DNA donor between A and B or A and B+C. The fourth and final approach involved conditioning on two common DNA donors between A and B or A and B+C. As more information was applied to the analysis, the greater the increase in the LR for the comparison of the target sample to the POI. Conditioning on two common donors between the target and the background provided almost the same amount of information as conditioning on the references of the known background DNA donors. This resulted in an increase in the LR that was over 10 orders of magnitude for known donors in the target sample. Here we have demonstrated the value in collecting additional background samples from an area adjacent to a targeted sample, and that this has the potential to improve discrimination power., Competing Interests: Conflict of interest The authors declare that they have no conflict of interest., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Forensic laboratories often sample weapons and clip-seal plastic bags (CSPB) used to package illicit material for the purpose of identifying the handler(s). However, there may be other explanations as to how a person's DNA was transferred to such items. This may include an individual storing the item among their personal belongings for somebody else or the item being stored among their belongings without their knowledge. Here we investigate the direct transfer of DNA to knives and CSPB during handling and explore two feasible alternative explanations related to the indirect transfer of DNA to these items in residential environments. The handling of DNA-free items was performed by 10 individuals who were instructed, on separate occasions, to cut a foam board in half and fill a CSPB with a drug substitute. To explore indirect transfer, sets of these items were (a) placed on kitchen benches and coffee/dining tables for ∼1 min, or (b) stored for two days in kitchen and bedroom drawers within the homes of 10 individuals. After each of the three scenarios, samples were collected from the knife handle and blade, the body and seal of the CSPB, and the surface the items were placed on, the latter as a measure to gain insight into the presence of prevalent and/or background DNA. DNA transfer was observed under all three scenarios, though more frequently when items were handled or stored for 2 days, compared to when placed on a surface for ∼1 min. Under the latter scenario, DNA, if present, was below the level of detection in many samples and produced no profile, suggesting that detectable DNA transfer occurs to a lesser degree from static brief contacts. The study results and associated probabilities will assist forensic examiners with their interpretation of case circumstances regarding the transfer and recovery of DNA from these items., Competing Interests: Declaration of Competing Interest The authors declare no conflict of interest., (Copyright © 2023 Elsevier B.V. All rights reserved.)

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., Competing Interests: Conflicts of interest The authors have no conflicts of interest to declare., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)

The increased sensitivity of current DNA profiling technologies allows the detection of trace amounts of DNA. With these advancements, there is an increased probability of detecting trace levels of DNA from contamination. Studies which investigate the accumulation and transfer of DNA within forensic laboratories provide insight into the possible mechanisms which may result in the contamination of exhibits. To gain a greater understanding of the level of DNA transfer between exhibit packaging and forensic workspaces, the accumulation of DNA within an operational forensic exhibit storeroom was investigated. Samples were collected from previously cleaned forensic exhibit storeroom shelves at various time points over a 14-week period. To determine the source of accumulating DNA, profiles generated from shelf samples were compared to the laboratory staff elimination database and the profiles generated from exhibits stored on each of the shelves sampled over the course of the study. Additionally, all samples were compared using STRmix™ mixture-to-mixture profile analysis, to identify the presence of common non-staff DNA donors and DNA from exhibits stored on the shelves sampled. As sampling time intervals increased, there was a significant increase in DNA quantity (ng) and number of profile contributors. The shelf height was also observed to influence the number of profile contributors, with higher numbers of contributors being found on lower shelves. DNA profiles generated from the shelf samples were matched to DNA from forensic staff members who enter the storeroom and police employees, who do not enter the storeroom. There were three instances where a common DNA profile contributor was identified between a shelf sample and the profile generated from an exhibit.This study provides insight into whether current exhibit storage procedures are still adequate given the highly sensitive DNA profiling systems currently used., (Copyright © 2022 Elsevier B.V. All rights reserved.)

DNA samples recovered from items of clothing are often attributed to the wearer and one or more individuals who may have contacted the item during an alleged criminal activity. Another scenario often proposed by defence counsel is that DNA was transferred from a previously contacted item/surface unrelated to the activity of interest onto the item of clothing. Under such scenarios, DNA may also be transferred from the clothing to the item/surface with which it comes into contact. One such surface is flooring, upon which clothing may be placed while not being worn or may be contacted during wearing, such as falling or being forced to the ground. This study investigates the transfer of DNA to and from clothing and flooring when different contacts are applied between the two surfaces in an environment representative of what investigators would encounter in routine casework, a residential environment. Participants were provided with two sets of new and unused upper and lower garments to wash then wear for ~8 h inside their own home before storing them in paper evidence bags. The two sets of clothing were taken to a home occupied by unrelated individuals, where one set was placed on the floor ('passive') by the researcher while the other was worn by the participant who laid with their back on the floor, rolled to one side and back, then stood up ('active'). Within the houses sampled, the main bedroom was targeted as flooring types and histories of use were more consistent across houses and less variation in DNA profile composition was previously observed for samples collected in the same room. Samples were collected from predetermined areas of the clothing and flooring where contact did and did not occur. Reference profiles were obtained from wearers and individuals they lived with, as well as occupants of the home. DNA transfer was observed from clothing to flooring and from flooring to clothing in both 'active' and 'passive' situations, though greater where a situation involved the application of pressure and friction ('active'), and only where contact between clothing and flooring occurred. Results from this study inform on the composition of DNA profiles one is likely to obtain from an item of clothing or a flooring surface following a similar contact event between the two substrates and will aid investigators when interpreting DNA evidence recovered in a domestic environment and the activities leading to its transfer and subsequent recovery., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Current forensic DNA profiling kits and techniques enable the detection of trace amounts of DNA. With advancements in kit sensitivity, there is an increased probability of detecting DNA from contamination. Research into DNA transfer within operational forensic laboratories provides insight into the possible mechanisms that may lead to exhibit contamination. To gain a greater understanding of the potential for evidence bags to act as DNA transfer vectors, the level of DNA accumulating on the exterior of evidence bags during the exhibit examination process was investigated. The exterior of 60 evidence bags were tapelifted before and after the examination of the exhibit inside of the bag resulting in 120 DNA profiles. These DNA profiles were compared to DNA profiles of staff working within the building and samples taken from the exhibit inside the bag. Common DNA profile contributors from each sample were also identified through STRmix™ mixture to mixture analysis. The average DNA quantity and number of profile contributors was higher in samples taken from the bag before exhibit examination than after examination. Fifty six percent of all samples taken identified a match between DNA recovered from the evidence bag and at least one staff member. On 11 bags, a common contributor was identified between the exhibit in the bag and the exhibit package post-examination. In one instance a DNA profile, matching that of a donor, on the exhibit bag before examination was also detected on a sample taken from the exhibit, raising the possibility of outer bag-to-exhibit DNA contamination. This study demonstrates that operational forensic laboratories must consider exhibit packages as a potential source of DNA contamination and evaluate their exhibit handling and storage procedures accordingly., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Due to improved laboratory techniques, touched surfaces and items are increasingly employed as sources of forensic DNA evidence. This has urged a need to better understand the mechanisms of DNA transfer between individuals. Shedder status (i.e. the propensity to leave DNA behind) has been identified as one major factor regulating DNA transfer. It is known that some individuals tend to shed more DNA than others, but the mechanisms behind shedder status are largely unknown. By comparing the amounts of DNA deposited from active hands (i.e. used "as usual") and inactive hands (i.e. not allowed to touch anything), we show that some of the self-DNA deposited from hands is likely to have accumulated on hands from other parts of the body or previously handled items (active hands: 2.1 ± 2.7 ng, inactive hands: 0.83 ± 1.1 ng, paired t-test: p = 0.014, n = 27 pairs of hands). Further investigation showed that individual levels of deposited DNA are highly associated with the level of DNA accumulation on the skin of the face (Pearson's correlation: r = 0.90, p < 0.00001 and Spearman's ranked correlation: r s = 0.56, p = 0.0016, n = 29). We hypothesized that individual differences in sebum secretion levels could influence the amount of DNA accumulation in facial areas, but no such correlation was seen (Pearson's correlation: r = - 0.13, p = 0.66, n = 14). Neither was there any correlation between DNA levels on hands or forehead and the time since hand or face wash. We propose that the amount of self-DNA deposited from hands is highly influenced by the individual levels of accumulated facial DNA, and that cells/DNA is often transferred to hands by touching or rubbing one's face., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

DNA evidence on shoes can play an important role in solving a variety of crimes. We investigated the transfer, persistence, prevalence and recovery of DNA (DNAtppr) on shoes (sneakers) and their soles in realistic handling scenarios taking into account the shedder status. This study aims to increase the understanding of the expected composition of DNA profiles and their probative value, providing a basis for activity level assessments. Samples were analyzed using a direct lysis method, suggesting its versatility and increasing the DNA typing success compared to previous studies on footwear. The data showed surface-dependent background DNA (bDNA) levels on shoe soles and prevalence of bDNA on the upper parts of the shoe. The owner of the shoe was allocatable to the mixture for almost every shoe and sampling location. Alternating scenarios of shoe handling were simulated through different pairs of shedders to distinguish shoe owner and subsequent user. Secondary users were attributable to DNA mixtures regardless of shedder status after wearing shoes a single time. The influence of the shedder status follows specific trends in this context. However, particularly intermediate shedders show inconsistent results. The prevalence of bDNA appears to have a greater effect on the impact of the shedder status on DNA profile composition than previously reported. The data help researchers to better resolve suspect statements and determine if a person of interest wore the shoes relevant to the investigation., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Due to advances in DNA profiling sensitivity as well as the implementation of various types of software to analyse these profiles, forensic biologists can provide opinions about results generated from very low levels of template DNA. The ability to obtain DNA profiles from such 'trace' DNA brings into question the mechanisms of transfer which led to it being deposited. This study investigates the level of DNA that is deposited by an individual to their work environment. DNA collection plates were placed at distances from 0.5 to 5 m from individuals' office desks and left for 1 day to 6 weeks before being swabbed and profiled with GlobalFiler. The results from this study indicate that an individual can deposit DNA in areas they were present, even if surfaces and/or objects were not directly contacted and even after only one day. Distance from a person, the length of time and the person themselves all play a role in the quantity of DNA that is deposited to one's surroundings., (Copyright © 2021 Elsevier B.V. All rights reserved.)

In forensic investigations involving stolen and crashed vehicles, examining airbags for the presence of saliva is useful strategy in order to try and establish who the driver of the vehicle may have been. The use of an evaluative approach in these types of investigations allows the forensic scientist to evaluate the significance of the evidence with regard to two alternative hypothesis. The presence of saliva on an airbag may be the result of the driver coming into contact with it during an impact. Alternatively, the saliva may have transferred to the airbag from another area in the vehicle following its deployment. To address this question and attach significance to this finding, a dataset on the prevalence and persistence of saliva is required, alongside relevant background information on the case. The purpose of this study was to determine if saliva matching the main driver of a vehicle is present in the areas immediately surrounding the driver's section, and also to determine the persistence of saliva in vehicles. Salivary-α-amylase was detected in 53% of all samples collected from vehicles. Saliva positive samples yielded statistically significantly (p<0.05) more DNA than saliva negative samples. There was no statistical difference in DNA yields from the different areas sampled in the vehicles. The steering wheel was observed to have the greatest number of saliva positive samples (80%). The driver's DNA profile was detected in 72% of the total samples taken. We demonstrated that saliva can persist for at least ten days in vehicles in daily use. This study has produced a useful dataset that can be utilised under certain conditions by forensic investigators when taking an evaluative approach to these particular types of forensic investigations., (Copyright © 2021 Elsevier B.V. All rights reserved.)

DNA transfer is a well-recognised phenomenon impacting the probability of detecting the presence of a particular source of DNA and thus the likelihood of the evidence given considered events within forensic investigations. Comprehensive study is lacking on variables associated with indirect DNA transfer without physical contact. Additionally, the drying properties of forensically relevant biological materials are under researched despite the recognised potential for these properties to affect DNA transfer. This study investigated the drying properties and indirect DNA transfer of dried blood, saliva, semen, vaginal fluid and touch DNA without contact deposited on two different non-porous hard substrates (melamine and glass) and two different porous soft substrates (polyester and cotton) by tapping (all substrates) and stretching (only fabric substrates) agitations. Different apparent drying trends were observed between the volumes, substrates and biological materials tested with substrate type generally having a greater influence than biological material. The rate and percentage of indirect transfer appeared to be dependent on agitation, substrate type, biological material and its drying properties. The outcomes of this study may assist those evaluating the likelihood of the evidence given proposed events during activity level assessments., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Firearms are the most relevant items of evidence in gun-related crimes, likely bearing various traces facilitating an objective reconstruction of the crime. Trace DNA recovered from firearm surfaces might help to identify individual(s) having handled the firearm and thereby possibly to link the firearm and the corresponding shooter, however, the interpretation of DNA traces on handled items can be challenging and requires a detailed understanding of various factors impacting DNA prevalence, transfer, persistence and recovery. Herein, we aimed at improving our understanding of factors affecting the variability of trace DNA characteristics recovered from firearms handled in gun-related crimes: Skin contact traces were recovered from various outer surfaces of two types of firearms handled in four realistic, casework-relevant handling scenarios and the corresponding trace characteristics (DNA yield, number of contributors, relative profile contribution for known and unknown contributors, LRs) were compared. Trace DNA characteristics differed distinctly between handling conditions, firearm and surface types as well as handling individuals and intraindividual deposits emphasizing the variability and complexity of trace DNA profile composition expected to be recovered from firearms after realistic handling scenarios. The obtained results can provide useful insights for forensic experts evaluating alternative activity level propositions in gun-related crimes., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Sexual assault cases are regularly encountered in forensic laboratories. The victim's underwear and other clothes are often submitted with the intention of retrieving the offender's DNA. We examined six sexual assault scenarios; removing underwear, removing brassiere, digital penetration of the vagina from the front, grabbing breasts over the top of the brassiere, digital penetration of the vagina from the rear, and grabbing the breasts under the brassiere from the rear. For each scenario we used a dummy weighing approximately 45 kg to mimic a victim and recorded where the underwear was contacted and how much DNA was transferred using volunteer 'offenders'. We found that how much DNA was recovered depended on which individual acted as offender and suggest it depends on the shedder status of the offender. We also discovered instances of the spouse, or office co-worker of the offender on the underwear. The obtained results will assist in identifying areas to target on underwear for different sexual assault scenarios, and also will provide important information that can be used for assigning probabilities of DNA transfer aiding evaluations of forensic biology findings that consider activity level propositions., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Cellular material derived from contact traces can be transferred via many direct and indirect routes, with the manner of contact and the time of transfer (in relation to the alleged crime-event) having an impact on whether DNA is recovered from the surface and a reportable profile generated. In an effort to acquire information on the transfer and recovery of DNA traces from clothing items worn during scenarios commonly encountered in casework, upper garments were worn during a normal working day before individuals were paired to embrace one another ('contact'), go on an outing together ('close proximity'), or individually asked to spend a day in another person's environment ('physical absence'). Each prescribed activity was repeated by sixteen individuals across four countries, and was the last activity performed before the garment was removed. Samples were collected from several areas of the upper garments and processed from DNA extraction through to profiling within the laboratory of the country in which the individual resided. Activities relating to the garment prior to and during wearing, including the prescribed activity, were recorded by the participant and considered during the interpretation of results. In addition to obtaining reference profiles from the wearer and their activity partner, DNA profiles from the wearers' close associates identified in the questionnaire were obtained to assess the impact of background DNA transferred prior to the prescribed activity. The wearer was typically, but not always, observed as the major contributor to the profiles obtained. DNA from the activity partner was observed on several areas of the garment following the embrace and after temporarily occupying another person's space. Particular areas of the garment were more prone to acquiring the hugging partner or office owner's DNA than others, and whether they were observed as the major or minor component was activity dependent. For each of the pairs, no DNA from the activity partner was acquired by the garments during the outing, even though both participants were in close proximity. This study provides empirical data on the transfer, persistence, prevalence and recovery of DNA from clothing items, and enables a better understanding of the mechanisms which lead to the transfer and detectability of DNA traces in different scenarios., (Copyright © 2020 Elsevier B.V. All rights reserved.)

There is a need to improve our awareness of the transfer, persistence, prevalence and recovery of DNA (DNA-TPPR) from items/surfaces, and within different spaces and circumstances, to assist sample targeting during collection and activity level assessments. Here we investigate DNA-TPPR within office spaces. Specifically, to what extent DNA, left by a temporary user of an office space that has been occupied by a regular user for an extended period, is detectable when the duration of their temporary occupancy and their general activities are known. Also, how readily the DNA of the regular user is still detectable after a known period of occupancy by another person, and to what extent DNA of others is present. Samples were collected from 18 core items/surfaces within eight single use office spaces that had been used temporarily by another occupant for 2.5-7 h. Four of these offices were within one forensic laboratory and four within another. Each lab collected and processed the samples to generate DNA profiles using their own set of methodologies. The owner/regular user of an office space was found to be the major/majority contributor to profiles from most items within the space, even after temporary use by another person. The detectability of the temporary occupier of an office space varied among offices and items. The temporary occupier was not observed on all items touched. In most instances, when detected, the temporary occupier was known to have touched the surface at some stage. Therefore, where one is seeking to collect samples that may detect a temporary user of a space, it is advisable to target several potentially touched sites. A difference in methodologies applied from collection through to profiling appears to impact DNA yields and profile types. Ascertaining the impact of using different methodologies on the profiles generated from collected samples, requires further research. More research is also needed to generate data to help determine frequency estimates for different types of profiles given different user histories of an item or space., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Trace DNA and the manner in which it is transferred from item to item is a common topic arising in forensic science, both in case evaluations, and in Court testimony. In order to assign the probability of obtaining DNA findings, given competing propositions that specify transfer mechanisms, consideration must be given to a number of factors. Previous work by the authors developed a simple Object-Oriented Bayesian Network (OOBN) that pooled numerous published studies in order to attempt evaluation of trace DNA results given such propositions. In this work, we expand on the previously published OOBN and formalise a number of class networks that can be used together in a logical way to consider DNA movement through complex chains of transfer events. Specifically, we develop an OOBN that considers the two-way transfer of DNA that occurs when two items contact, and allows for the sampling of intermediary items involved in the chain of transfers. The aim is to show that adopting an approach involving basic building blocks, we offer the possibility to tackle complex and various cases for which the OOBN will be obtained by combining their elementary blocks. We conclude with a demonstration of applying the OOBN being applied to a chain of transfers in a case scenario., (Copyright © 2019 Elsevier B.V. All rights reserved.)

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., (Copyright © 2019 Elsevier B.V. All rights reserved.)

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., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Sharing data between forensic scientists on DNA transfer, persistence, prevalence and recovery (TPPR) is crucial to advance the understanding of these issues in the criminal justice community. We present the results of a collaborative exercise on reporting forensic genetics findings given activity level propositions. This exercise outlined differences in the methodology that was applied by the participating laboratories, as well as limitations to the use of published data on DNA TPPR. We demonstrate how publication of experimental results in scientific journals can be further improved to allow for an adequate use of these data. Steps that can be taken to share and use these data for research and casework purposes are outlined, and the prospects for future sharing of data through publicly accessible databases are discussed. This paper also explores potential avenues to proceed with implementation and is intended to fuel the discussion on sharing data pertaining to DNA TPPR issues. It is further suggested that international standardization and harmonization on these topics will benefit the forensic DNA community as it has been achieved in the past with the harmonization of STR typing systems., (Crown Copyright © 2018. Published by Elsevier B.V. All rights reserved.)

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., (Copyright © 2018 Elsevier B.V. All rights reserved.)

In alleged sexual assault investigations, the detection of male DNA on female intimate swabs can be established through Y-STR profiling. However, in cases where the defendant lives in the same dwelling as the complainant, the defendant may argue that his DNA was transferred through normal social contact, and dispute that intimate contact occurred. This study aimed to determine whether or not male DNA could be detected in samples collected from the vaginal cavity after everyday activities. A total of 300 samples from eight individuals were subjected to DNA quantification and Y-STR amplification. Three donors reported sexual contact during the time of sampling, hence the detection of male-specific DNA in post-coital samples was concomitantly evaluated. The majority of samples (n=237, 79%) were undetermined for male DNA by real-time PCR quantification. No Y-STR profiles having three or more alleles were obtained in these samples, with the exception of three samples which displayed three alleles each. One sample was collected six days post-coital, one sample likely presented artefacts, and one exhibited two alleles at the same locus. Male-specific quantification values were obtained for the remaining 63 samples (21%), however only 31 samples displayed alleles at three or more loci. Twenty-three of the 63 samples showed inhibition during real-time PCR quantification, and the majority of these exhibited no Y-STRs. A further three samples were excluded from the dataset due to possible contamination. The maximum confirmed time frame for obtaining a full Y-STR profile was six days post-coital, but may be longer in some donors. Overall concordance between DNA quantification and Y-STR amplification was 85.8%. This study demonstrates that obtaining a Y-STR profile comprising three or more alleles from a vaginal swab collected from a woman who has not participated in recent intimate sexual activities is not indicated. This suggests that there is unlikely to be detectable adventitious transfer of DNA from male individuals living in the same household as a female donor. However, approximately one in seven samples may display 1-2 unexpected allelic peaks (<400 RFU). These are unlikely to originate from the male partner or cohabitant of the donor and should be interpreted with extreme caution, and with every effort attempted to replicate results before a conclusion is derived about their relevance. These findings support the significance of male DNA profiles consisting of more than three alleles obtained from female intimate samples during investigations of alleged sexual assault., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Questions relating to how DNA from an individual got to where it was recovered from and the activities associated with its pickup, retention and deposition are increasingly relevant to criminal investigations and judicial considerations. To address activity level propositions, investigators are typically required to assess the likelihood that DNA was transferred indirectly and not deposited through direct contact with an item or surface. By constructing a series of Bayesian networks, we demonstrate their use in assessing activity level propositions derived from a recent legal case involving the alleged secondary transfer of DNA to a surface following a handshaking event. In the absence of data required to perform the assessment, a set of handshaking simulations were performed to obtain probabilities on the persistence of non-self DNA on the hands following a 40min, 5h or 8h delay between the handshake and contact with the final surface (an axe handle). Variables such as time elapsed, and the activities performed and objects contacted between the handshake and contact with the axe handle, were also considered when assessing the DNA results. DNA from a known contributor was transferred to the right hand of an opposing hand-shaker (as a depositor), and could be subsequently transferred to, and detected on, a surface contacted by the depositor 40min to 5h post-handshake. No non-self DNA from the known contributor was detected in deposits made 8h post-handshake. DNA from the depositor was generally detected as the major or only contributor in the profiles generated. Contributions from the known contributor were minor, decreasing in presence and in the strength of support for inclusion as the time between the handshake and transfer event increased. The construction of a series of Bayesian networks based on the case circumstances provided empirical estimations of the likelihood of direct or indirect deposition. The analyses and conclusions presented demonstrate both the complexity of activity level assessments concerning DNA evidence, and the power of Bayesian networks to visualise and explore the issues of interest for a given case., (Copyright © 2017 Elsevier B.V. All rights reserved.)

To address questions on the activity that led to the deposition of biological traces in a particular case, general information on the probabilities of transfer, persistence and recovery of cellular material in relevant scenarios is necessary. These figures may be derived from experimental data described in forensic literature when conditions relevant to the case were included. The experimental methodology regarding sampling, DNA extraction, DNA typing and profile interpretation that were used to generate these published data may differ from those applied in the case and thus the applicability of the literature data may be questioned. To assess the level of variability that different laboratories obtain when similar exhibits are analysed, we performed an inter-laboratory study between four partner laboratories. Five sets of 20 cable ties bound by different volunteers were distributed to the participating laboratories and sampled and processed according to the in-house protocols. Differences were found for the amount of retrieved DNA, as well as for the reportability and composition of the DNA profiles. These differences also resulted in different probabilities of transfer, persistence and recovery for each laboratory. Nevertheless, when applied to a case example, these differences resulted in similar assignments of weight of evidence given activity-level propositions., (Copyright © 2017 Elsevier B.V. All rights reserved.)

The presence of DNA in a criminal investigation often requires scrutiny in relation to how it came to be where it was found. There is a paucity of data with respect to the extent to which one can assume that the last person handling an object, which has previously been touched by others, will contribute to the DNA profile generated from it. There are limited data in detailing the extent to which any foreign DNA is picked-up from a previously touched object and transferred to subsequently touched objects. This study focuses on DNA transfer and persistence on a knife handle after multiple handlings with the knife by different individuals soon after each other, as well as handprints left on flat DNA-free surfaces immediately after touching a knife handle with a known history of prior handling. The profiles of later handlers of a knife are more prominent than earlier handlers; however, the last handler is not always the major contributor to the profile. Proportional contributions to the profiles retrieved from knife handles vary depending on the individuals touching the knife handle. They can also vary when knife handles have been handled in the same manner by the same individuals in the same sequence on different occasions. Hands readily pickup DNA left on objects by others and transfer it to subsequently touched objects. The quantity of foreign DNA picked up by a hand and deposited on subsequently touched objects diminishes as more DNA-free objects are handled soon after each other. Caution is advised when considering how DNA from different individuals may have been transferred to the object from which it was collected., (Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.)