An investigation into the transference and survivability of human DNA following simulated manual strangulation with consideration of the problem of third party contamination

Approach considerations for the management of strangulation in the emergency department

Patients with a history of strangulation present to the emergency department with a variety of different circumstances and injury patterns. We review the terminology, pathophysiology, evaluation, management, and special considerations for strangulation injuries, including an overview of forensic considerations and legal framework for strangulation events.

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.

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.

Profiling in wildlife crime: Recovery of human DNA deposited outside

Incidents of bird of prey persecution receive a lot of media coverage in the UK, with investigations rarely recovering sufficient evidence to proceed to prosecution. One of the main challenges is to identify a suspect, as these offences are carried out in remote locations without witnesses, and crime scenes may not be found for days. However, traps, poisoned baits and bird of prey carcasses can be recovered from these crime scenes. This study aimed to determine whether reportable human DNA profiles could be recovered from any of these substrates after periods of time outside. Experiments depositing human touch DNA on duplicate substrates (traps, rabbit baits and corvid carcasses) set for 0, 1, 2, 4, 7 and 10 days outside were carried out, with DNA recovery and profiling following standard operating procedures for Scottish Police Authority Forensic Services. Weather conditions varied among experiments, including some heavy rainfall. Results demonstrated that it was possible to obtain reportable DNA profiles from all substrates after at least 1 day outside. Most promisingly, the traps showed no drop-off in DNA persistence over the experiments as complete DNA profiles were obtained after the full 10 days outside. A further experiment using 4 bird of prey carcasses confirmed that it is possible to obtain reportable human DNA profiles from them after 1 day outside (n = 2 reportable profiles). These results show that touch DNA can persist in an outdoor environment, and provide a tantalising avenue for inquiry in bird of prey persecution investigations.

City-scale distribution and dispersal routes of mycobiome in residences

BACKGROUND

Pathogenic and allergenic bacteria and fungi within the indoors can bring detrimental health effects on the occupants. We previously studied the bacterial communities found in households located throughout Hong Kong as well as the skin surfaces of the occupants. As a complementary study, here, we investigated the fungal communities (mycobiome) in the same residences and occupants and identified factors that are important in shaping their diversity, composition, distribution, and dispersal patterns.

RESULTS

We observed that common skin and environmental fungal taxa dominated air, surface, and skin samples. Individual and touch frequency strongly and respectively shaped the fungal community structure on occupant skin and residential surfaces. Cross-domain analysis revealed positive correlations between bacterial and fungal community diversity and composition, especially for skin samples. SourceTracker prediction suggested that some fungi can be transferred bidirectionally between surfaces and skin sites, but bacteria showed a stronger dispersal potential. In addition, we detected a modest but significant association between indoor airborne bacterial composition and geographic distance on a city-wide scale, a pattern not observed for fungi. However, the distance-decay effects were more pronounced at shorter local scale for both communities, and airflow might play a prominent role in driving the spatial variation of the indoor airborne mycobiome.

CONCLUSIONS

Our study suggests that occupants exert a weaker influence on surface fungal communities compared to bacterial communities, and local environmental factors, including air currents, appear to be stronger determinants of indoor airborne mycobiome than ventilation strategy, human occupancy, and room type.

Defining background DNA levels found on the skin of children aged 0-5 years

There are currently no data available regarding the normal levels of DNA found on the skin of children engaging in routine day to day activities to assist with the forensic interpretation of DNA profiles generated from skin surface swabs. To address this deficit, skin surface swab samples were collected from 12 face/neck sites and 20 body sites on 50 children less than 5 years old. After exclusion of spoilt samples, 60 sets of swabs from 47 children (30 face/neck, 30 body) comprising of 944 individual samples were analysed. The number of alleles observed which could have originated from the child and the number which must have come from another source (non-child) were analysed. The following variables were evaluated: age, kissing, feeding and washing practices, number of contacts and application of cream. Overall, extremely small amounts of non-child DNA were retrieved from skin swabs. Child only (46.3 %) or no DNA at all (18.6 %) was observed for 64.9 % of all swabbed samples. Low levels of non-child DNA (1–5 alleles) were observed on 31.6 % of all swabs tested with only 3.4 % of swabs showing six or more alleles. A great deal of variation between children and between sites in the levels of both child DNA and non-child DNA was observed. A multilevel model, taking account of clustering within children, showed that there was a strong direct association between the amounts of child and non-child DNA observed. There was no relationship between the amount of DNA recovered and the demographic and biographic variables analysed. These background data have the potential to assist the analysis of DNA from the skin of children during criminal investigation.

The influence of substrate on DNA transfer and extraction efficiency

The circumstances surrounding deposition of DNA profiles are increasingly becoming an issue in court proceedings, especially whether or not the deposit was made by primary transfer. In order to improve the currently problematic evaluation of transfer scenarios in court proceedings, we examined the influence a variety of nine substrate types (six varieties of fabric, plywood, tarpaulin, and plastic sheets) has on DNA transfer involving blood. DNA transfer percentages were significantly higher (p=0.03) when the primary substrate was of non-porous material (such as tarpaulin, plastic or, to a lesser degree, wood) and the secondary substrate porous (such as fabrics). These findings on transfer percentages confirm the results of previous studies. Fabric composition was also shown to have a significant (p=0.03) effect on DNA transfer; when experiments were performed with friction from a variety of fabrics to a specific weave of cotton, transfer percentages ranged from 4% (flannelette) to 94% (acetate). The propensity for the same nine substrates to impact upon the efficiency of DNA extraction procedures was also examined. Significant (p=0.03) differences were found among the extraction efficiencies from different materials. When 15μL of blood was deposited on each of the substrates, the lowest quantity of DNA was extracted from plastic (20ng) and the highest quantities extracted from calico and flannelette (650ng). Significant (p<0.05) differences also exist among the DNA extraction yield from different initial blood volumes from all substrates. Also, significantly greater (p<0.05) loss of DNA was seen during concentration of extracts with higher compared to lower initial quantities of DNA. These findings suggest that the efficiency of extraction and concentration impacts upon the final amount of DNA available for analysis and that consideration of these effects should not be ignored. The application of correction factors to adjust for any variation among extraction and concentration efficiencies among substrates is proposed.

An evaluation of the transfer of saliva-derived DNA

Studies of DNA transfer have focused largely on the transfer of sloughed off epithelial cells from individuals' hands. This research examines primary, secondary, and tertiary transfer events involving DNA originating from saliva, a commonly encountered body fluid. More routine human behaviors were simulated to evaluate transfer, and the effects of drying time, moisture, and surface composition were investigated. The results agree with previous findings which indicate that the presence of moisture, as well as a smooth nonporous surface as the primary substrate, increases the efficiency of transfer. Previous transfer studies have found that the last individual to come into contact with an item is usually the major contributor to the resulting DNA mixture, unless conditions are simulated in which a "good shedder" serves as the primary depositor and a poor shedder serves as the secondary depositor. The results of this study indicate that when saliva is the source of the transferred DNA, the primary depositor is often the major contributor. These findings suggest that shedder status is less relevant with regard to touch DNA samples in a forensic setting and emphasize the need for caution when analyzing such samples.

DNA transfer within forensic exhibit packaging: potential for DNA loss and relocation

Crime scene samples after their collection are packaged and transported to the laboratory for examination and DNA analysis. The amount and location of DNA-containing material retrieved from an exhibit can be critical in acquiring a profile for incrimination or exclusion purposes and for elucidating criminal events. This paper shows that significant quantities of DNA are frequently: (a) transferred from the exhibit to the inside of the packaging and (b) transferred from its area of initial deposit to other areas of the same exhibit and/or to other exhibits within the same package. There is a distinct possibility of failing to generate adequate profiles in instances where the DNA content may otherwise have been adequate, and for the misinterpretation of a result that could impact negatively on the criminal investigation and court outcome. These findings highlight the need for improvements in the collection and packaging of forensic casework exhibits for DNA analysis.

Forensic trace DNA: a review

DNA analysis is frequently used to acquire information from biological material to aid enquiries associated with criminal offences, disaster victim identification and missing persons investigations. As the relevance and value of DNA profiling to forensic investigations has increased, so too has the desire to generate this information from smaller amounts of DNA. Trace DNA samples may be defined as any sample which falls below recommended thresholds at any stage of the analysis, from sample detection through to profile interpretation, and can not be defined by a precise picogram amount. Here we review aspects associated with the collection, DNA extraction, amplification, profiling and interpretation of trace DNA samples. Contamination and transfer issues are also briefly discussed within the context of trace DNA analysis. Whilst several methodological changes have facilitated profiling from trace samples in recent years it is also clear that many opportunities exist for further improvements.

Trace evidence characteristics of DNA: A preliminary investigation of the persistence of DNA at crime scenes

The successful recovery of trace or contact DNA is highly variable. It is seemingly dependent on a wide range of factors, from the characteristics of the donor, substrate and environment, to the delay between contact and recovery. There is limited research on the extent of the effect these factors have on trace DNA analysis. This study investigated the persistence of trace DNA on surfaces relevant to the investigation of burglary and robbery offences. The study aimed to limit the number of variables involved to solely determine the effect of time on DNA recovery. Given that it is difficult to control the quantity of DNA deposited during a hand contact, human buffy coat and DNA control solution were chosen as an alternative to give a more accurate measure of quantity. Set volumes of these solutions were deposited onto outdoor surfaces (window frames and vinyl material to mimic burglary and 'bag snatch' offences) and sterile glass slides stored in a closed environment in the laboratory, for use as a control. Trace DNA casework data was also scrutinised to assess the effect of time on DNA recovery from real samples. The amount of DNA recovered from buffy coat on the outdoor surfaces declined by approximately half over two weeks, to a negligible amount after six weeks. Profiles could not be obtained after two weeks. The samples stored in the laboratory were more robust, and full profiles were obtained after six weeks, the longest time period tested in these experiments. It is possible that profiles may be obtained from older samples when kept in similarly favourable conditions. The experimental results demonstrate that the ability to recover DNA from human cells on outdoor surfaces decreases significantly over two weeks. Conversely, no clear trends were identified in the casework data, indicating that many other factors are involved affecting the recovery of trace DNA. Nevertheless, to ensure that valuable trace evidence is not lost, it is recommended that crime scenes are processed expeditiously.

Investigation into "normal" background DNA on adult necks: implications for DNA profiling of manual strangulation victims

Others have investigated the role that DNA profiling could play as a method for identifying the perpetrator of manual strangulation. These studies have demonstrated that it is possible to collect offender DNA from the skin surface of a victim following physical contact. It is not known whether nonself biological material is normally present on the skin surface due to adventitious transfer occurring during innocent everyday interactions. To test the hypothesis that detectable amounts of nonself DNA are normally present on the skin surface of healthy adult individuals due to the adventitious transfer of DNA occurring during normal day-to-day social interactions, we designed an experiment in three phases. Phase 1 was used to deduce which DNA collection, extraction, and amplification methods were suited to investigating this question. During phase 2, the neck surface of 24 healthy adult volunteers was swabbed. DNA was extracted using the QIAamp DNA mini kit and amplified using the SGM Plus PCR amplification kit, using 28 PCR cycles. The work carried out during phase 3 involved a simulated assault to investigate primary and secondary transfer of DNA during physical contact. It was found that 23% of neck areas swabbed during phase 2 of this investigation showed nondonor alleles in the resulting DNA profile, with 5% of areas showing six or more nondonor alleles. The results of phase 3 showed that primary, secondary, and zero transfer of victim and/or offender DNA could be observed after physical contact and that alleles from an unknown source could still be detected in this more controlled experiment. The data presented in this paper demonstrate that DNA profiles generated after swabbing the skin surface of healthy adults can include components of an unknown source, present due to adventitious transfer. These components, if present in large quantities, have the potential to interfere with DNA profile interpretation of swabs taken for the investigation of physical assault by DNA profiling.

Investigation into the usefulness of DNA profiling of earprints

DNA profiling of biological trace evidence has been used for many years. The application of this technique specifically to the DNA profiling of earprints has not to date been thoroughly investigated. This report presents the results of 60 earprints collected from three healthy adult volunteers under controlled laboratory conditions. DNA profile analysis revealed that high levels of non-donor alleles are observed when earprints are collected for DNA profiling. The source of these non-donor alleles is investigated and the impact that their presence within the profile may have on the use of this technique is discussed.

Retrieval of DNA from the faces of children aged 0-5 years: a technical note

Approximately 21% of children suffer from some form of physical abuse. It is hypothesized that when an individual hits a child some of that person's DNA will be deposited onto the child's skin. As yet, no one has reported a method of sampling DNA from the skin of this vulnerable group of individuals. We have sampled DNA from several facial areas of 30 children aged 5 years of age and under. The results show that it is possible to swab the faces of this age group without distressing them or contaminating the samples. Additionally the results indicate that the DNA obtained is almost entirely that of the subject, with little nondonor DNA being observed.

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

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

The tendency of individuals to transfer DNA to handled items

This research investigates factors influencing the transfer of DNA to handled objects and the process known as 'shedding'. Volunteers were recruited to hold sterile plastic tubes using experiments originally designed by Lowe et al. [A. Lowe, C. Murray, J. Whitaker, G. Tully, P. Gill, The propensity of individuals to deposit DNA and secondary transfer of low level DNA from individuals to inert surfaces, Forensic Sci. Int. 129 (2002) 25-34]. Transferred cellular material was collected from the tubes and STR profiles generated using the AmpFlSTR SGM Plus multiplex with 28 and 34 PCR cycles. Volunteers were asked to hold the tubes with each hand, and to participate in a series of handwashing experiments. The DNA profiling results obtained from the transferred skin cells were compared. An attempt was made to characterize the volunteers as 'good' or 'bad' shedders and to establish which, if any, of the experimental variables were associated with 'good' shedding. Our results suggest that many factors significantly influence shedding, including which hand an individual touches an item with and the time that has elapsed since they last washed their hands. We have found that it may be more complicated than previously reported to categorise a person as being either a 'good' or a 'bad' shedder and that if truly 'good' shedders exist they may be significantly rarer than some have estimated. In the current research no 'good' shedders were observed in a group of 60 volunteers. Given these results, it seems that rather than being applied to individual forensic cases, knowledge of shedding characteristics will be most useful in providing general background data for the interpretation of trace DNA evidence.

The effectiveness of protective clothing in the reduction of potential DNA contamination of the scene of crime

The use of ultra-sensitive low copy number (LCN) DNA typing allows the analysis of picogram amounts of DNA. Trace evidence accidentally left at a scene of crime (SOC) by the investigating team may be inadvertently collected and analysed, potentially leading to spurious evidence being introduced into the criminal investigation. A series of experiments were undertaken to determine the extent to which an investigator could contribute to any DNA contamination of a scene of crime under different simulated activities. Further, the degree to which any contamination was reduced by the use of commercially available protective clothing was demonstrated. Precautions that should routinely be taken at a scene of crime to reduce the risk of DNA contamination are recommended.

Fingerprints as evidence for a genetic profile: morphological study on fingerprints and analysis of exogenous and individual factors affecting DNA typing

Material recovered from 374 fingerprints left by eleven laboratory workers on three different substrates (glass, wood, metal) at a standard pressure time of 30 s, with and without preliminary handwashing, was submitted to morphological, quantitative, and type analysis. Morphological and agarose-gel electrophoresis analysis showed that a non-negligible amount of epidermal corneal cells presented apoptotic alterations. The quantity of DNA recovered from fingerprints ranged between 0.04 to 0.2 ng, and in a significant number of experiments no DNA was detected. Handwashing reduced the amount of DNA recovered from fingerprints. The "shedder status" of the donor was a very important factor, causing inter-individual variations in the amount of DNA left by fingerprints. Spurious alleles from laboratory-based and secondary transfer contamination, stutters, and other artifacts described when analyzing low-copy-number DNA and capable of affecting correct profiles were observed.