Prevalence of human cell material: DNA and RNA profiling of public and private objects and after activity scenarios

Where did it go? A study of DNA transfer in a social setting

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.

Transfer and persistence of intruder DNA within an office after reuse by owner

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.

The role of cats in human DNA transfer

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.

Investigative use of human environmental DNA in forensic genetics

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.

Trace DNA and its persistence on various surfaces: A long term study investigating the influence of surface type and environmental conditions - Part one, metals

It is imperative for proper evidence triage that forensic biologists understand what kind of results to expect from certain evidence types submitted for DNA analysis. The persistence of trace DNA has been insufficiently investigated and there is little data available pertaining to the persistence of DNA in different environmental conditions and on different materials. The goal of this study is to increase the available data on this topic which would, in turn, help forensic biologists manage expectations when submitting specific evidence types for DNA testing. The work presented herein is a large-scale persistence project aimed to identify trends in the persistence of trace DNA and indicate how different environmental storage conditions and target surface characteristics influence the persistence of cellular and cell free DNA (cfDNA) over time. To eliminate variation within the experiment we used a proxy DNA deposit consisting of a synthetic fingerprint solution, cellular DNA, and/or cfDNA. Samples were collected and analysed from 7 metals over the course of 1 year (27 time points) under 3 different environmental storage conditions. The results of this experiment show that metal type greatly influences DNA persistence. For instance, copper exhibited an expected poor DNA persistence (up to 4 h) which a purification step did not help increase the DNA yield. Alternatively, DNA can persist for up to a year on lead at levels potentially high enough to allow for forensic DNA testing. Additionally, this study showed that the sample storage environment had no impact on DNA persistence in most cases. When considering DNA type, cfDNA was shown to persist for longer than cellular DNA and persistence as a whole appears to be better when DNA is deposited as mixtures over when deposited alone. Unsurprisingly, it can be expected that DNA recovery rates from trace deposits will decrease over time. However, DNA decay is highly dependent on the metal surface and extremely variable at short time points but slightly less variable as time since deposition increases. This data is intended to add to our understanding of DNA persistence and the factors which affect it.

A study of DNA transfers onto plastic packets placed in personal bags

The ability to detect low level DNA brings with it the uncertainty of whether the detected DNA is a result of transfer. To address this uncertainty, a simulation study was conducted in which a mock illicit drug packet was placed into the personal bags of individuals. When the average transit time of the packets was increased from around 2 h to more than 14 h, the percentage of the DNA profiles recovered from the packets which could be attributed to the individuals increased greatly from 5.3% to 48.6%. We found that drug packers who were poor shedders could not be included as contributors to the DNA profiles from the drug packets at all and there was a higher chance that individuals other than themselves could be included as contributors to the DNA profile recovered from drug packets. We also found that it was equally likely that the drug packers who had direct contact with the drug packets and bag owners who did not, could be included as contributors to the DNA profiles recovered from the packets. The results in this study highlight the importance of taking into consideration the transit time of drug packet, the shedder status of the alleged packer and the history of an item, when evaluating DNA evidence in the context of illicit drug activities.

Comparison of massively parallel sequencing to capillary electrophoresis for short tandem repeat genotyping of trace DNA

In forensic genetics, massively parallel sequencing (MPS) offers several advantages over the current golden standard, capillary electrophoresis (CE): additional sequence information, shorter amplicon lengths, and the simultaneous analysis of many markers. These benefits result in a reduced number of reactions necessary while improving the amount of data obtained, thereby conserving valuable sample extracts. This proves particularly advantageous for the analysis of trace DNA. This study assessed the suitability of MPS for short tandem repeat (STR) typing of low template samples compared with results obtained through CE. The MPS genotypes showed higher concordance to reference genotypes, with donor alleles being more frequently assigned to be the major contributor, meeting the requirements for database entry. However, the MPS workflow is more time-consuming and associated with higher costs.

Trace DNA Transfer in Co-Working Spaces: The Importance of Background DNA Analysis

The presence of background DNA (bgDNA) can hinder the evaluation of DNA evidence at the activity level, especially when the suspect is expected to be retrieved due to their habitual occupation of the investigated environment. Based on real-life casework circumstances, this study investigates the prevalence, composition, origin, and probable transfer routes of bgDNA found on personal items in situations where their owner and person of interest (POI) share the same workspace. Baseline values of bgDNA were evaluated on the participants' personal items. Secondary and higher degree transfer scenarios of non-self DNA deposition were also investigated. The DNA from co-workers and co-inhabiting partners can be recovered from an individual's personal belongings. Non-self DNA present on the hands and deposited on a sterile surface can generate uninformative profiles. The accumulation of foreign DNA on surfaces over time appears to be crucial for the recovery of comparable profiles, resulting in detectable further transfer onto other surfaces. For a thorough evaluation of touch DNA traces at the activity level, it is necessary to collect information not only about DNA transfer probabilities but also about the presence of the POI as part of the 'baseline' bgDNA of the substrates involved.

Determining the number and size of background samples derived from an area adjacent to the target sample that provide the greatest support for a POI in a target sample

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 cm2) yielding significantly more DNA than smaller background samples (30 cm2). 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.

The invisible witness: air and dust as DNA evidence of human occupancy in indoor premises

Humans constantly shed deoxyribonucleic acid (DNA) into the surrounding environment. This DNA may either remain suspended in the air or it settles onto surfaces as indoor dust. In this study, we explored the potential use of human DNA recovered from air and dust to investigate crimes where there are no visible traces available-for example, from a recently vacated drugs factory where multiple workers had been present. Samples were collected from three indoor locations (offices, meeting rooms and laboratories) characterized by different occupancy types and cleaning regimes. The resultant DNA profiles were compared with the reference profiles of 55 occupants of the premises. Our findings showed that indoor dust samples are rich sources of DNA and provide an historical record of occupants within the specific locality of collection. Detectable levels of DNA were also observed in air and dust samples from ultra-clean forensic laboratories which can potentially contaminate casework samples. We provide a Bayesian statistical model to estimate the minimum number of dust samples needed to detect all inhabitants of a location. The results of this study suggest that air and dust could become novel sources of DNA evidence to identify current and past occupants of a crime scene.

Presence of Human DNA on Household Dogs and Its Bi-Directional Transfer

Awareness of the factors surrounding the transfer of DNA from a person, item, or surface to another person, item, or surface is highly relevant during investigations of alleged criminal activity. Animals in domestic environments could be a victim, offender, or innocent party associated with a crime. There is, however, very limited knowledge of human DNA transfer, persistence, prevalence, and recovery (DNA TPPR) associated with domestic animals. This pilot study aimed to improve our understanding of DNA TPPR associated with domestic dogs by collecting and analysing samples from various external areas of dogs of various breeds, interactions with humans, and living arrangements, and conducting a series of tests to investigate the possibility of dogs being vectors for the indirect transfer of human DNA. Reference DNA profiles from the dog owners and others living in the same residence were acquired to assist interpretation of the findings. The findings show that human DNA is prevalent on dogs, and in the majority of samples, two-person mixtures are present. Dogs were also found to be vectors for the transfer of human DNA, with DNA transferred from the dog to a gloved hand during patting and a sheet while walking.

A synthetic fingerprint solution and its importance in DNA transfer, persistence and recovery studies

A review of the literature on DNA transfer and persistence highlights many difficulties that are encountered when conducting research of this nature. One of the main problems highlighted repeatedly in the literature is the prevalence of inherent uncontrolled variation that accompany these studies, and in turn, the results obtained. This work aims to decrease the amount of intrinsic variability associated with DNA transfer and persistence experiments using a realistic proxy solution which is adaptable, of known composition, reproducible, and capable of being standardised. This proxy is composed of three parts: a synthetic fingerprint solution, cellular DNA, and cell free DNA. In this proof-of-concept study the proxy was tested with a small-scale DNA transfer and recovery experiment and the data obtained suggests that the use of a solution that mimics real fingerprint secretions, over an alternative (such as buffer or a body fluid), is important when working with non-donor provided trace DNA samples. This is because the DNA deposit solution likely impacts the transfer of DNA from fingers/hands to a surface as well as the ability to recover the biological material once deposited.

Persistence of touch DNA on commonly encountered substrates in different storage conditions

The persistence of touch DNA deposited after realistic handling of items typically encountered in forensic investigations has been the subject of few studies. Understanding the long-term persistence of touch DNA on different substrates in varying conditions can be central to the effective triage of samples for further processing. As the time between an alleged incident and collection of evidence may vary from a few days to years after an alleged event, this study assessed three different common substrates for the persistence of touch DNA over a time span up to 9 months. These substrates included fabric, steel, and rubber, each of which were handled in a way to imitate what may happen during a criminal act. The three substrates were exposed to two different environments for up to 9 months: inside a dark cupboard with no traffic to act as a control and an outside semi-exposed environment. Ten replicates from each of the 3 substrates were tested at 5 time points to create 300 samples. All samples were processed using a standard operating workflow to provide genotype data after exposure to different environments. It was found that the fabric samples produced informative STR profiles (defined here as 12 or more alleles) up to the 9 month timepoint for either environment. The rubber and steel substrates for the inside condition produced informative STR profiles up to the 9 month timepoint, but only generated informative STR profiles for the outside condition up to 3 and 6 months, respectively. These data add to our understanding of the external factors that affect DNA persistence.

Direct and Secondary Transfer of Touch DNA on a Credit Card: Evidence Evaluation Given Activity Level Propositions and Application of Bayesian Networks

In a judiciary setting, questions regarding the mechanisms of transfer, persistence, and recovery of DNA are increasingly more common. The forensic expert is now asked to evaluate the strength of DNA trace evidence at activity level, thus assessing if a trace, given its qualitative and quantitative features, could be the result of an alleged activity. The present study is the reproduction of a real-life casework scenario of illicit credit card use by a co-worker (POI) of its owner (O). After assessing the shedding propensity of the participants, differences in DNA traces' qualitative and quantitative characteristics, given scenarios of primary and secondary transfer of touch DNA on a credit card, a non-porous plastic support, were investigated. A case-specific Bayesian Network to aid statistical evaluation was created and discrete observations, meaning the presence/absence of POI as a major contributor in both traces from direct and secondary transfer, were used to inform the probabilities of disputed activity events. Likelihood Ratios at activity level (LRα) were calculated for each possible outcome resulting from the DNA analysis. In instances where only POI and POI plus an unknown individual are retrieved, the values obtained show moderate to low support in favour of the prosecution proposition.

Recovery techniques for contact DNA traces

Donor DNA profiling can serve at least two purposes: 1) to enhance the evidential value of DNA deposited on garments/ items and 2) to provide valuable tactical information during crime scene investigation. In this review, different types of methods for the recovery of the contact DNA traces have been summarized. Additionally, with the available techniques, the unique characteristics and limitations thereof have been overviewed. The aim of this paper is to review the techniques of touch traces collection. Techniki odzyskiwania śladów kontaktowych DNA Profilowanie DNA dawcy może służyć co najmniej dwóm celom: 1) zwiększeniu wartości dowodowej DNA zdeponowanego na odzieży/przedmiotach oraz 2) dostarczeniu cennych informacji taktycznych podczas badania miejsca przestępstwa. W niniejszym przeglądzie podsumowano różne rodzaje metod odzyskiwania śladów kontaktowych DNA. Dodatkowo, w odniesieniu do dostępnych technik, dokonano przeglądu ich unikalnych cech i ograniczeń. Celem niniejszej pracy jest przegląd technik pozyskiwania śladów dotykowych.

Reporting on forensic biology findings given activity level issues in the Netherlands

There appears to be some hesitation within the forensic biology community to formally evaluate and report on findings given activity level propositions. This hesitance in part stems from concerns about the lack of relevant data on the dynamics of biological traces and doubt about the relevance of such expert opinions to the trier of fact. At the Netherlands Forensic Institute formal evaluative opinions on the probability of case findings given propositions at the activity level are provided since 2013, if requested by a mandating authority. In this study we share the results from a retrospective analysis of 74 of such requests. We explore which party initiates requests, the types of cases that are submitted, the sources of data being used to assign probabilities to DNA transfer, persistence, prevalence and recovery (TPPR) events, the conclusions that were drawn by the scientists, and how the conclusions were used by the courts. This retrospective analysis of cases demonstrates that published sources of data are generally available and can be used to address DNA TPPR events in most cases, although significant gaps still remain. The study furthermore shows that reporting on forensic biology findings given activity level propositions has been generally accepted by the district and appeal courts, as well as the other parties in the criminal justice system in the Netherlands.

The DNA-Buster: The evaluation of an alternative DNA recovery approach

Touch DNA recovery techniques can have limitations, as their effectiveness depends on the substrate on which the DNA of a person of interest can be found. In this study, an in-house dry-vacuuming device, the DNA-Buster, was compared to traditional methods for its DNA recovery performance from items typically examined in forensic casework. The aim was to evaluate whether this dry-vacuuming approach can recover DNA efficiently, potentially complementing the well-established recovery strategies. For this, the performances of swabbing, taping, wet- (M-Vac®) and dry-vacuuming (DNA-Buster) were investigated quantitatively and qualitatively for touch DNA deposited on carpet, cotton sweater, stone, tile and wood. For the sweater, both vacuuming methods outperformed the other collection tools quantitatively. While the highest DNA amounts for the carpet were yielded by swabbing and taping, dry-vacuuming was equally good in reaching full DNA profiles, whereas less complete profiles were observed for the M-Vac®. For stone and tile, swabbing was optimal, whereas dry-vacuuming clearly underperformed for these substrates. Taping was the best recovery method for wood. Despite applying single donor DNA after thoroughly cleaning the items, undesired DNA mixtures were detected for all recovery techniques and all substrates. The overall research findings show first that the novel dry-vacuuming method is suited for DNA recovery from textiles. Secondly, they indicate that more attention should be paid to the substrate-collection dependency to ensure best practices in recovering genetic material in a precise, confident and targeted manner from the variety of forensic casework material.

DNA accumulation and transfer within an operational forensic exhibit storeroom

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.

Comparison of genotyping and weight of evidence results when applying different genotyping strategies on samples from a DNA transfer experiment

In this study, we assessed to what extent data on the subject of TPPR (transfer, persistence, prevalence, recovery) that are obtained through an older STR typing kit can be used in an activity-level evaluation for a case profiled with a more modern STR kit. Newer kits generally hold more loci and may show higher sensitivity especially when reduced reaction volumes are used, and this could increase the evidential value at the source level. On the other hand, the increased genotyping information may invoke a higher number of contributors in the weight of evidence calculations, which could affect the evidential values as well. An activity scenario well explored in earlier studies [1,2] was redone using volunteers with known DNA profiles. DNA extracts were analyzed with three different approaches, namely using the optimal DNA input for (1) an older and (2) a newer STR typing system, and (3) using a standard, volume-based input combined with replicate PCR analysis with only the newer STR kit. The genotyping results were analyzed for various aspects such as percentage detected alleles and relative peak height contribution for background and the contributors known to be involved in the activity. Next, source-level LRs were calculated and the same trends were observed with regard to inclusionary and exclusionary LRs for persons who had or had not been in direct contact with the sampled areas. We subsequently assessed the impact on the outcome of the activity-level evaluation in an exemplary case by applying the assigned probabilities to a Bayesian network. We infer that data from different STR kits can be combined in the activity-level evaluations.

Touch DNA Sampling Methods: Efficacy Evaluation and Systematic Review

Collection and interpretation of "touch DNA" from crime scenes represent crucial steps during criminal investigations, with clear consequences in courtrooms. Although the main aspects of this type of evidence have been extensively studied, some controversial issues remain. For instance, there is no conclusive evidence indicating which sampling method results in the highest rate of biological material recovery. Thus, this study aimed to describe the actual considerations on touch DNA and to compare three different sampling procedures, which were "single-swab", "double-swab", and "other methods" (i.e., cutting out, adhesive tape, FTA® paper scraping), based on the experimental results published in the recent literature. The data analysis performed shows the higher efficiency of the single-swab method in DNA recovery in a wide variety of experimental settings. On the contrary, the double-swab technique and other methods do not seem to improve recovery rates. Despite the apparent discrepancy with previous research, these results underline certain limitations inherent to the sampling procedures investigated. The application of this information to forensic investigations and laboratories could improve operative standard procedures and enhance this almost fundamental investigative tool's probative value.

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.

Transfer, persistence and recovery of DNA and mRNA vaginal mucosa markers after intimate and social contact with Bayesian network analysis for activity level reporting

In sexual assault cases, it can be challenging to identify the type of body fluids/ cell types present in a crime scene sample, especially the origin of epithelial cells. Therefore, more labs are applying mRNA body fluid analysis for saliva, skin and vaginal mucosa markers. To address activity level propositions, it is necessary to assign probabilities of transfer, persistence, prevalence and recovery of DNA and mRNA markers. In this study we analysed 158 samples (fingernail swabs, penile swabs and boxershorts) from 12 couples collected at different time points post intimate contact and after non-intimate contact in order to detect DNA from the person of interest (POI) and mRNA vaginal mucosa markers. Samples were DNA and RNA co-extracted and analysed with PowerPlex®Fusion 6C System and 19-plex mRNA primer mix respectively, using Endpoint PCR and the CE platform. Vaginal mucosa was detected up to 36 h post intimate contact, but also detected in one non-intimate contact sample. In 94% of intimate contact and 50 % of non-intimate contact samples the DNA results support the proposition that POI is the donor (LR ≥ 10,000). There was a strong association between the detection of vaginal mucosa and the average RFU value of the POI. The data were used to instantiate a comprehensive Bayesian network to evaluate the evidence at activity level, given alternate propositions conditioned upon indirect or direct transfer events. It is shown that the value of the evidence is mainly affected by the high DNA quantity (measured as mean RFU) that is recovered from the POI. The detection of vaginal mucosa had low impact upon the resultant likelihood ratio.

Transfer and persistence of DNA on items routinely encountered in forensic casework following habitual and short-duration one-time use

Empirical data obtained from controlled experiments is necessary to ensure that sound expert opinion evidence is provided regarding transfer and persistence of DNA in criminal proceedings. Knowledge in this area is also required at the outset of criminal investigations, to ensure that the proposed examinations can assist with answering questions that are relevant to forensic investigations. This study aimed to provide such data by examining the relative and absolute quantities of DNA deposited on items that are routinely submitted to the forensic laboratory by a habitual user, defined as someone who used it for ~1 week, and a subsequent one-time user. We found that the quantity of DNA deposited on routine household items spanned a broad range. The habitual user's DNA was detected on most items as the major donor, regardless of whether it was subsequently handled by another person for a short period of time. The one-time, short duration, user's DNA was detected on approximately two thirds of the items, albeit typically at quantities lower than the habitual user. Most of the household items we examined also had detectable DNA deposits from at least one other, unknown individual, typically in low quantities. Attempts to clean non-porous items with readily available household cleaners were partially effective but failed to completely eliminate detectable DNA from a habitual user in most cases.

Development and validation of a fast and automated DNA identification line

The importance of DNA evidence for gaining investigative leads demands a fast workflow for forensic DNA profiling performed in large volumes. Therefore, we developed software solutions for automated DNA profile analysis, contamination check, major donor inference, DNA database (DDB) comparison and reporting of the conclusions. This represents the Fast DNA IDentification Line (FIDL) and this study describes its development, validation and implementation in criminal casework at the authors' institute. This first implementation regards single donor profiles and major contributors to mixtures. The validation included testing of the software components on their own and examination of the performance of different DDB search strategies. Furthermore, end-to-end testing was performed under three conditions: (1) testing of scenarios that can occur in DNA casework practice, (2) tests using three months of previous casework data, and (3) testing in a casework production environment in parallel to standard casework practices. The same DNA database candidates were retrieved by this automated line as by the manual workflow. The data flow was correct, results were reproducible and robust, results requiring manual analysis were correctly flagged, and reported results were as expected. Overall, we found FIDL valid for use in casework practice in our institute. The results from FIDL are automatically reported within three working days from receiving the trace sample. This includes the time needed for registration of the case, DNA extraction, quantification, polymerase chain reaction and capillary electrophoresis. FIDL itself takes less than two hours from intake of the raw CE data to reporting. Reported conclusions are one of five options: (1) candidate retrieved from DDB, (2) no candidate retrieved from DDB, (3) high evidential value with regards to reference within the case, (4) results require examination of expert, or (5) insufficient amount of DNA obtained to generate a DNA profile. In our current process, the automated report is sent within three working days and a complete report, with confirmation of the FIDL results, and signed by a reporting officer is sent at a later time. The signed report may include additional analyses regarding e.g. minor contributors. The automated report with first case results is quickly available to the police enabling them to act upon the DNA results prior to receiving the full DNA report. This line enables a uniform and efficient manner of handling large numbers of traces and cases and provides high value investigative leads in the early stages of the investigation.

GITAD 2020: quality assurance test through 20 years of experience

GITAD (Grupo Iberoamericano de Trabajo en Análisis de DNA) was founded in 1998 as the first operational group of AICEF (Academia Iberoamericana de Criminalística y Estudios Forenses), formally created in 1999. The mission and the vision of GITAD are to promote the development of forensic genetics in Ibero-American countries and to achieve the maximum level of innovation and quality in each country, and with that aim, a proficiency test was developed. Since 1999, the member laboratories receive four reference samples with the objective of obtaining the genetic profile with their routine protocols, a theoretical exercise since 2003, and since 2007, it was incorporated a forensic sample, which changes every year. The consensus results and the different discrepancies are discussed in an annual meeting. This article illustrates the evolution of the proficiency test through 20 years from different points of view: the increase of participant laboratories, the evolution of the different DNA typing techniques reported by the Ibero-American participant laboratories, the challenges that the proficiency test have met, and future perspectives for a continuous improvement of the proficiency test, especially regarding its accreditation under ISO 17043.

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.

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.

On the Identification of Body Fluids and Tissues: A Crucial Link in the Investigation and Solution of Crime

Body fluid and body tissue identification are important in forensic science as they can provide key evidence in a criminal investigation and may assist the court in reaching conclusions. Establishing a link between identifying the fluid or tissue and the DNA profile adds further weight to this evidence. Many forensic laboratories retain techniques for the identification of biological fluids that have been widely used for some time. More recently, many different biomarkers and technologies have been proposed for identification of body fluids and tissues of forensic relevance some of which are now used in forensic casework. Here, we summarize the role of body fluid/ tissue identification in the evaluation of forensic evidence, describe how such evidence is detected at the crime scene and in the laboratory, elaborate different technologies available to do this, and reflect real life experiences. We explain how, by including this information, crucial links can be made to aid in the investigation and solution of crime.

Determination of shedder status: A comparison of two methods involving cell counting in fingerprints and the DNA analysis of handheld tubes

The shedder status of an individual may be important to consider in the context of DNA transfer, persistence and recovery and in Bayesian networks where a person's shedder status may have an impact on the outcome. In this study we compared two methods to determine shedder status: the handheld tube (HH) method and a fluorescent cell count (CC) method. A poor association was observed between the numbers of detected cells in a fingerprint using the CC method and the strength of the DNA result with the HH method. The 20 participants were classified into low (25%), medium (50%) and high (25%) shedders based on the HH method. While the low and high shedders showed a good consistency between the replicates, the medium shedders varied more and have to be considered more carefully as they may act as either a high or a low shedder in an event of DNA transfer.

Sampling touch DNA from human skin following skin-to-skin contact in mock assault scenarios-A comparison of nine collection methods

Collection of touch DNA from an offender on the victim's skin can provide relevant evidence for investigations of criminal cases. Therefore, the choice of the optimal sample collection method is crucial. In this study, we investigated the recovery of STR profiles from touch DNA on human skin by comparing nine different collection methods: the dry and wet cotton swabs in three different movements, the double-swab (wet-dry) method, the wet and dry Copan FLOQSwabs™, and the Scene Safe FAST™ minitapes. Mock assault scenarios were conducted with a male offender grasping the forearms of a female victim. Samples were collected from the assaulted area of the victim's skin, and the recovery of the offender's STR profile was evaluated. Our results indicate that the different swabs and swabbing techniques did not have a distinct impact on the STR recovery; however, the lowest STR recovery was achieved with Scene Safe FAST™ minitapes. In addition, we compared the double-swab method to the single-swab method by analyzing the DNA quantity of the wet and dry swabs separately. We found on average 13.7% more offender DNA using the double-swab method, but this did not translate into higher STR recovery. Our findings indicate that several methods perform equally well when collecting touch DNA from human skin, although SceneSafe FAST™ minitapes seem to be the least adequate for this purpose.

An LR framework incorporating sensitivity analysis to model multiple direct and secondary transfer events on skin surface

Bayesian logistic regression is used to model the probability of DNA recovery following direct and secondary transfer and persistence over a 24 h period between deposition and sample collection. Sub-source level likelihood ratios provided the raw data for activity-level analysis. Probabilities of secondary transfer are typically low, and there are challenges with small data-sets with low numbers of positive observations. However, the persistence of DNA over time can be modelled by a single logistic regression for both direct and secondary transfer, except that the time since deposition must be compensated by an offset value for the latter. This simplifies the analysis. Probabilities are used to inform an activity-level Bayesian Network that takes account of alternative propositions e.g. time of assault and time of social activities. The model is extended in order to take account of multiple contacts between person of interest and 'victim'. Variables taken into account include probabilities of direct and secondary transfer, along with background DNA from unknown individuals. The logistic regression analysis is Bayesian - for each analysis, 4000 separate simulations were carried out. Quantile assignments enable calculation of a plausible range of probabilities and sensitivity analysis is used to describe the corresponding variation of LRs that occur when modelled by the Bayesian network. It is noted that there is need for consistent experimental design, and analysis, to facilitate inter-laboratory comparisons. Appropriate recommendations are made. The open-source program written in R-code ALTRaP (Activity Level, Transfer, Recovery and Persistence) enables analysis of complex multiple transfer propositions that are commonplace in cases-work e.g. between those who cohabit. A number of case examples are provided. ALTRaP can be used to replicate the results and can easily be modified to incorporate different sets of data and variables.

Prevalence of DNA of regular occupants in vehicles

People will deposit, redistribute and remove biological traces when they interact with their environment. Understanding the dynamics of trace DNA is crucial to assess both the optimal sampling strategy to recover traces and the relevance of DNA evidence in the context of a case. This paper addresses the prevalence of DNA of drivers, passengers, and unknown individuals in vehicles. Five vehicles with a regular driver only, and five vehicles with a regular driver and regular passenger have each been sampled at twenty locations. Based on the findings, we propose a sampling strategy for investigative purposes as well as for evaluative purposes when evaluating the findings given scenarios that propose the person-of-interest as either the driver or passenger in a vehicle.

mRNA profiling of mock casework samples: Results of a FoRNAP collaborative exercise

In recent years, forensic mRNA profiling has increasingly been used to identify the origin of human body fluids. By now, several laboratories have implemented mRNA profiling and also use it in criminal casework. In 2018 the FoRNAP (Forensic RNA Profiling) group was established among a number of these laboratories with the aim of sharing experiences, discussing optimization potential, identifying challenges and suggesting solutions with regards to mRNA profiling and casework. To compare mRNA profiling methods and results a collaborative exercise was organized within the FoRNAP group. Seven laboratories from four countries received 16 stains, comprising six pure body fluid / tissue stains and ten mock casework samples. The laboratories were asked to analyze the provided stains with their in-house method (PCR/CE or MPS) and markers of choice. Five laboratories used a DNA/RNA co-extraction strategy. Overall, up to 11 mRNA markers per body fluid were analyzed. We found that mRNA profiling using different extraction and analysis methods as well as different multiplexes can be applied to casework-like samples. In general, high input samples were typed with high accuracy by all laboratories, regardless of the method used. Irrespective of the analysis strategy, samples of low input or mixed stains were more challenging to analyze and interpret since, alike to DNA profiling, a higher number of markers dropped out and/or additional unexpected markers not consistent with the cell type in question were detected. It could be shown that a plethora of different but valid analysis and interpretation strategies exist and are successfully applied in the Forensic Genetics community. Nevertheless, efforts aiming at optimizing and harmonizing interpretation approaches in order to achieve a higher consistency between laboratories might be desirable in the future. The simultaneous extraction of DNA alongside RNA showed to be an effective approach to identify not only the body fluid present but also to identify the donor(s) of the stain. This allows investigators to gain valuable information about the origin of crime scene samples and the course of events in a crime case.

Investigation into the prevalence of background DNA on flooring within houses and its transfer to a contacting surface

When sampling an item or surface for DNA, the collection of 'background' DNA (bDNA) from previous use poses an issue as it may impact the detectability of 'target' DNA and the interpretation of the DNA results given alleged activities. This study investigates the prevalence and transferability of bDNA on flooring surfaces within occupied houses under conditions similar to those that are encountered in casework. To assess bDNA presence and transferability, and the impact of how and who contacts the surface, areas used frequently and infrequently were targeted in the kitchen, living room, bedroom and bathroom of five houses, and two samples taken from each area; one directly from the floor and another from a cotton surface after contacting the floor. DNA was detected in 97 % (of 39) of samples collected directly from flooring, with 92 % providing interpretable profiles. DNA was detected in 85 % (of 39) samples collected from cotton swatches after contacting the floors, with 79 % providing interpretable profiles. The overall quantity, number of contributors, and likelihood of observing a major contributor was greater for samples obtained directly from the floor compared to the cotton. In 80 % of samples recovered from cotton, the quantity of DNA recovered was less than 20 % of that which was recovered directly from the floor. Overall, no trend was observed between the level of reported activity by occupants within areas of the same room and the quantity of DNA recovered directly from the flooring, the quantity of DNA transferred to and recovered from the cotton, or the number of contributors in resulting DNA profiles. In contrast, greater quantities of DNA were generally obtained from houses with a greater number of occupants. Profile composition was similar for samples collected from different areas of the same room, irrespective of the level of activity and from where the sample was obtained (i.e. directly from the floor or contacting surface). Occupants were often not detected in DNA profiles collected from rooms they were known to use and could be observed in profiles collected from rooms they reportedly did not use. The findings of this preliminary investigation provide an understanding of the complexities of transfer, persistence, prevalence and recovery of DNA traces in houses occupied by multiple people and highlights the need to consider how and who uses a space, in the investigation of criminal activities where DNA traces are recovered from, or have been in contact with, flooring.

DNA transfer to firearms in alternative realistic handling scenarios

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.

Illuminating touch deposits through cellular characterization of hand rinses and body fluids with nucleic acid fluorescence

Forensic DNA typing from touched or handled items in routine casework is increasing as the sensitivity of detection techniques improves. Our understanding of the cellular/acellular content of touch deposits and the origins of the DNA therein is still limited. This work explores the cellular content of rinses from washed and unwashed hands, as well as saliva, nasal and eye washes which could be sources of transferred DNA onto hands. Flow cytometry and microscopic examination were used to detect granularity, size and nucleic acid fluorescence data. Cellular content did not vary significantly within an individual, although some differences were observed between donors. Saliva contained populations of nucleated epithelia as well as smaller cells and debris, all positive for DNA. Hand rinses consisted almost entirely of anucleate corneocytes, many of which also stained positive for nucleic acids. These data raise questions about shed corneocyte DNA content previously assumed to be negligible.

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.