Impact of several wearers on the persistence of DNA on clothes-a study with experimental scenarios

Self- and non-self-DNA on hands and sleeve cuffs

Studying DNA transfer and persistence has become increasingly important over the last decade, due to the impressive sensitivity of modern DNA detection methods in forensic genetics. To improve our understanding of background DNA that could also potentially be transferred, we analyzed the DNA composition on the outside of sleeve cuffs and sampled DNA directly from the hands of four different collaborators upon their arrival at work during 25 working days. Sampling of their hands was repeated after several hours working in our department. The shedder status of the participants, as assumed from previous internal studies, was well re-produced in the study. However, we noticed that the DNA shedding capacity could also change drastically during the day, with one participant showing a more than sixfold increase between hands sampled in the morning and hands sampled in the afternoon. As expected, poor DNA shedders carry more relative amounts of non-self-DNA on their hands than good shedders. Non-self-alleles were detected in 95% of the samples. We also observed potential effects of hand washing and the mode of transport to get to work on the DNA amount. People living with family members occasionally carried their DNA on their hands and more frequently on their sleeve cuffs. Sleeve cuffs, as being close to our hands, have a large potential to transfer DNA from one place to another, yet they have sparsely been studied as DNA transfer intermediates so far. In general, we collected consistently more DNA from the sleeve cuffs than from the hands of the participants, demonstrating their importance as potential transfer vectors. More DNA was recovered from sleeve cuffs made of synthetic fabric than from cuffs made of cotton or leather. In the afternoon, DNA from co-habitant family members could not be detected on the hands anymore and the detection of profiles from colleagues became more frequent. From two out of 100 analyzed sleeve cuffs and two out of 200 sampled hands, we established unknown major DNA profiles that would have been suitable for an entry in the national DNA database. This finding demonstrates the possibility to transfer DNA that has most likely been picked up somewhere in the public space.

Comparison of DNA recovery methods and locations from regularly-worn hooded jumpers before and after use by a second wearer

Items of worn clothing are routinely examined for DNA in forensic casework, commonly with the expectation that at least some of the DNA will come from a wearer of the item, so-called 'wearer DNA'. This study investigated DNA recovered from hooded jumpers that were regularly worn and laundered for four weeks and then subsequently worn by a different individual for four hours. This study also systematically investigated whether using different recovery methods or sampling locations on the jumpers might distinguish between DNA deposited by the regular and most recent wearers of clothing. Four volunteers each wore a new hooded jumper regularly (6 h/day, 2 days/week, washed at weekends) during two 4-week periods. At the end of each month, DNA was first recovered by cutting out and mini-taping the inside left cuff, half-collar, pocket and underarm fabric. The jumpers were then worn by a different individual for four hours, and DNA was again recovered by cutting out and mini-taping, but this time from the inside right cuff, half-collar, pocket and underarm fabric. All DNA samples (n = 128) were quantified and profiled. DNA quantities ranged from 0 to ∼40 ng with an outlier of ∼150 ng, and no significant differences were observed among recovery methods and sampling locations, nor whether one or two wearers had worn the jumpers. However, one volunteer consistently deposited significantly more DNA to their jumpers than two other volunteers, confirming the impact of 'shedder status' on DNA deposition during wearing of clothing. When jumpers were regularly worn by one wearer, the majority (72.7-83.3 %) of the samples for all wearers across both months comprised a major profile of the wearer with a minor profile of non-wearer alleles. When jumpers were then worn by a second wearer, the composition of the profiles obtained were generally reproducible across the recovery methods used, the sampling locations and the two replicates of the experiment for each pairing of wearers. However, profile compositions differed between wearer pairings. Overall, ∼60 % of profiles obtained gave a major profile of the regular wearer, whereas ∼30 % gave a major profile of the second wearer. The remaining profiles comprised other much less frequent observations of single-source profiles of each wearer and equal proportions of DNA from both wearers. Non-wearer DNA was also observed in the majority of samples, both before and after jumpers were worn by a second wearer. For one volunteer's jumpers, a recurring non-wearer DNA profile was observed that could be attributed to their romantic partner, and this DNA persisted on the jumpers even after being worn by the second wearer. This study provides insight on the impact of shedder status, multiple wearers, different recovery methods and sampling locations on the quantities of DNA and compositions of DNA profiles recovered from authentically regularly-worn hooded jumpers. The findings also provide a preliminary dataset that can be used to infer activity level probabilities in casework.

Evaluation of face masks as a valuable forensic DNA evidence in the post-COVID era

After the onset of COVID-19 pandemic, a sharp surge in the usage of the face-masks throughout the globe has been observed. Pre-experiment survey of 252 individuals indicated a higher use of cotton-make masks (41%), followed by N-95 make (31%), and surgical disposable masks (26%). It was also further revealed that a higher fraction of individuals wear a face-mask more than 3 times (37%) before its disposal. In order to assess the potential usability of different mask types as forensic DNA evidence, a study was conducted on 50 healthy individuals. DNA content of different fractions such as the portion of mask covering the mouth region and the ear-piece showed a good source of host DNA. Though no statistically significant difference (P < 0.05) was found in the DNA quantity obtained from different face mask types, an increasing trend was obtained in the order: cloth make type (7.031 ± 0.31 ng), N-95 make (4.711 ± 0.15 ng), and surgical disposable type (2.17 ± 0.13 ng). The time of wearing of a face-mask showed a positive correlation with the yield of DNA irrespective of the face-mask type used. Samples retrieved from both the portions covering the mouth area and the ear-piece showed a good source of genomic DNA yielding an average of 4.82 ± 0.11 ng and 4.44 ± 0.10 ng of DNA, respectively. Irrespective of the face-mask types, number of reuse, and the portion of the mask, 66.66-96.11% of samples showed a complete autosomal STR DNA profile. This suggests that if a face-mask is found at the crime scene, it should be collected and preserved as a potential source of DNA evidence for routine forensic DNA analysis.

DNA transfer between worn clothing and flooring surfaces with known histories of use

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.

About the influence of environmental factors on the persistence of DNA - a long-term study

DNA persistence and DNA transfer are important features in the assessment of a crime scene. The question how long DNA may persist at a certain location is similarly important as the one how the DNA has been transferred to this location. Depending on the source of the DNA as well as the conditions at the crime scene, the answer to this question is quite difficult. In this study, persistence of DNA from epithelial abrasions, blood cells, and saliva cells in indoor and outdoor scenarios has been investigated with regard to exposure time and exposure conditions including sunlight, temperature, and humidity in summer and winter scenarios. Overall, we generated 338 epithelial samples, 572 blood samples, and 572 saliva samples. A complete profile of the cell/DNA donor after exposure could be obtained in 47%, 65%, and 58% of epithelial abrasions, blood samples, and saliva samples, respectively. Regarding blood samples, there were no differences between supporting materials cloth and plastic; however, the percentage of complete profiles was higher for saliva samples on plastic and for epithelial samples on cloth. In indoor scenarios, complete profiles could be recovered from nearly all blood and saliva samples up to 9 months, whereas the amount of epithelial complete profiles already started to decline after 3 months. In outdoor scenarios, we observed a tipping point at an exposure time of 3 months. Blood and saliva samples collected after this period displayed complete profiles in less than 25% of samples. After 12 months, no outdoor sample showed a complete profile. The results of this study facilitate decisions on the relevance of recovered DNA from crime scenes.

Persistence of blood (DNA/RNA) on shoe soles under varying casework related conditions

Blunt force traumas by footwear can result in severe and even fatal head and upper body injuries. Oftentimes, footwear impressions are only partially available and evidential value is limited. DNA evidence on shoe soles could provide crucial evidence helping to solve crimes by linking target DNA to the activity of interest. Little is known about the persistence and detectability of biological material post such offenses and the interplay of factors affecting the analytical success. In this study, we assessed the persistence of blood on shoe soles under varying parameters such as blood location, different sneakers, weather condition, gait, amount of blood, underground and step count. We applied an optimized DNA/RNA workflow adapted to micro-traces without constraints for the primary DNA pipeline. There is a high probability to link donor DNA to the shoe sole for up to 300-400 steps, regardless of the underground, blood location, and amount of blood. Depending on the sole material and the degree of abrasion of the sole, a longer blood persistence can be observed. Considering blood, 98.2% of the initial DNA amount (1 μl initial blood volume) was lost after 100 steps walked on sole areas that are in constant contact with the ground. Proportion of foreign DNA was marginal (avg. 4.4 alleles), minimizing the probability of unintentional DNA transfer in this context. RNA typing showed high specificity but lower sensitivity than presumptive tests used for body fluid identification (BFI). Luminol is essential for targeted sampling on shoe soles, as latent blood traces (>100-200 steps) provided sufficient biological material for DNA/RNA typing. The generated data help to address the activity of interest and evaluate probabilities about prevalence of target DNA important for casework implications and assessments on activity level.

Casework-related DNA transfer on footwear in consideration of the shedder status

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.

Transfer of DNA without contact from used clothing, pillowcases and towels by shaking agitation

DNA is frequently retrieved from commonly used objects or surfaces with no apparent biological stains. This DNA may have come from one or more individuals who directly deposited their DNA, or indirectly transferred the DNA of others, when physically contacting the sampled object or surface. Furthermore, contactless indirect DNA transfer of this 'touch DNA' from fabric substrates was recently demonstrated to be possible in a controlled laboratory environment. The circumstances and extent to which this form of contactless DNA transfer occurs are largely unknown. This study investigated indirect DNA transfer without contact by applying a gentle shaking agitation to used clothing, pillowcases and towels, with known usage and history, of 10 volunteers above the collection zone of the secondary surface. DNA transfer frequently occurred and was possible from all three investigated items. It occurred at levels that often produced informative profiles where transferred profiles closely resembled the profiles generated from the primary item. The outcomes of this study contribute to expanding the understanding of indirect DNA transfer without contact. However, this field would benefit from investigating a wider range of agitations and/or item types with various histories of use to determine the level of transfer and its detectability under different conditions.

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.

"I've never been at the crime scene!" - gloves as carriers for secondary DNA transfer

Over recent years, DNA profiling techniques have become highly sensitive. Even small amounts of DNA at crime scenes can be analysed leading to new defence strategies. At court, defence lawyers rarely question the existence of a DNA trace (source level) but challenge how the DNA was transferred to the scene (activity level). Nowadays, the most common defence strategy is to claim that somebody else had stolen the defendant's gloves and used them while breaking and entering. In this study we tested this statement. Using gloves made of different material (cloth, leather, rubber) and varying secondary transfer surfaces (wood, metal, glass), we simulated a few of the most likely transfer scenarios that occur during breaking and entering. While we detected the presence of DNA on the outside of 92 of the 98 gloves tested, we observed only one case of secondary transfer in a total of 81 transfer experiments. This data demonstrates that secondary transfer under conditions resembling realistic conditions is a very rare event.

Casework direct kit as an alternative extraction method to enhance touch DNA samples analysis

Latent fingerprints are commonly found in crime scenes, and currently used in forensic analysis to obtain STR profiles from DNA recovered from finger contact. Analysis of STR profiles obtained from touch DNA has been very useful to elucidate crimes and the extraction method may be determinant for the recovery of genetic material collected from different surfaces. This study aimed to verify and compare the efficiency of two different extraction kits for processing touch DNA samples obtained from fingerprints deposited on computer keyboards, knife handles and exterior door handles and steering wheels of cars. One hundred and four experiments were conducted to simulate crime scenes and evaluate the efficiency of two extraction kits for touch DNA samples: the DNA IQ™ System and the Casework Direct Kit (both Promega Corporation). Each experiment was conducted with two individuals in order to obtain a mixture profile. The genetic material deposited was collected by double swab method (Sweet et al. 1997) and DNA quantification was conducted using Quantifiler Trio™ (ThermoFisher Scientific). Samples were amplified by PowerPlex® Fusion System kit (Promega). It was possible to obtain STR profiles for 32 (61.5%) out of the 52 extracted using DNA IQ and 51 (98.1%) out of the 52 extracted using the Casework Direct Kit. Samples extracted by DNA IQ had higher average of quantification values for long targets (>200bp) across all tested surfaces. That seems to be due to an incompatibility between the Quantifiler Trio and the Casework Direct Kit. Samples with positive quantification but without STR profile, as well as samples without quantification but with STR profiles were also observed. Statistical analysis showed that the Casework Direct Kit produced significantly more useful profiles than DNA IQ (p-value = 0.001), since these profiles had more STR markers with allelic correspondence to second donators present in the mixture. This study provides insights about the effect of different surfaces and extraction methods on recovery and generation of STR profiles. Limitations for the quantification step for these samples with a low quantity of DNA were highlighted as well. We concluded that the Casework Direct Kit was much more efficient for processing touch DNA samples than DNA IQ.

Interpol review of forensic biology and forensic DNA typing 2016-2019

This review paper covers the forensic-relevant literature in biological sciences from 2016 to 2019 as a part of the 19th Interpol International Forensic Science Managers Symposium. The review papers are also available at the Interpol website at: https://www.interpol.int/content/download/14458/file/Interpol%20Review%20Papers%202019.pdf.

DNA detection of a temporary and original user of an office space

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.

Secondary DNA transfer by working gloves

With the development of highly sensitive STR profiling methods, combined with sound statistical tools, DNA analysis on the (sub-)source level is hardly ever seriously questioned in court. More often, the exact mode of DNA transfer to the crime scene is questioned. In burglary cases, in particular when gloves are worn, secondary DNA transfer is often discussed as explanation for finding a DNA profile matching the accused because it is well known that gloves can act as a potential vector for indirect DNA transfer. In this study we investigated the shedder status as a possible factor influencing the extent of secondary DNA transfer to a crime scene, with the person committing the crime wearing working gloves. Firstly, the shedder status for 40 participants (20 male, 20 female) was determined, following a previously published procedure. Good shedders (n = 12) were found to deposit a higher amount and quality of DNA onto objects, compared to bad shedders (n = 25). Secondly, participants were paired into four groups (good with good; good with bad; bad with good; bad with bad), each group consisting of five pairs. The first participant (P1) of each pair used working gloves to pack and carry a box to simulate a house move. Two days later, the second participant (P2) of the pair wore the same pair of gloves to simulate a burglary, using a screwdriver as a break-in tool. After taking swabs of the outside and inside of a glove (primary DNA transfer) and the handle of the screwdriver (secondary DNA transfer), full DNA analysis was performed. Our experiments show that good shedders, overall, deposit more DNA than bad shedders, both onto the outside and the inside of the glove, regardless of being P1 or P2. When conducting the experiments with two participants sharing the same shedder status, no significant differences occurred in the number of deposited alleles. In six out of 19 cases a DNA profile matching P1 was found (binary LR>10⁶) on the screwdriver and in all six cases P1 was a good shedder. Our results indicate that the shedder status of an individual affects the extent of DNA transfer. They further confirm the possibility of an innocent person's DNA profile being found on an object they never handled.

Touch DNA: impact of handling time on touch deposit and evaluation of different recovery techniques: An experimental study

"Touch DNA" is DNA obtained from biological material transferred from a donor to an object or a person during physical contact. This particular kind of evidence could play an essential role in forensic laboratory work and is considered an important tool for investigators. Even though the principal aspects of "Touch DNA" have been extensively studied, to date, there are few reports in the research field of DNA retrieval from garments that have been worn. This study aimed to investigate the "handling time", analyzing particularly the minimum contact time required to deposit a sufficient amount of DNA on a garment to produce an interpretable profile of the "handler". Moreover, three different sampling techniques were compared ("dry swab", "cutting out", and "adhesive tape") with the aim of defining the technique that guarantees the best recovery of the three methods tested. Analyzing the data of this experimental model, a "handling time" of two seconds is enough to release sufficient DNA on to a garment to obtain a complete profile. Moreover, this study demonstrated that when targeting for foreign DNA, the sample area should be narrowed down as much as possible to the smallest area possible to maximize target DNA recovery.

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

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.