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

The Role of Molecular Investigations in Estimating the Time since Deposition (TSD) of Bloodstains: A Systematic Review of the Literature

At many crime scenes, investigators are able to trace and find traces of blood. For many years, it was believed that such traces could only be subjected to genetic investigations, such as those aimed at comparing DNA profiling with a suspect to verify his identity, and that it was therefore not possible to backdate the traces. In recent years, various works have used experimental models to investigate the possibility of identifying markers and methodologies for estimating the time since deposition (TSD) of bloodstains. Despite the results, these methods are still not part of standard procedures, and there is no univocal analysis methodology. In this work we carried out a systematic literature review of all the papers published in the last ten years on this topic, comparing the experimental models created. This review demonstrates the potential that different molecular approaches, such as transcriptomics, metabolomics, proteomics, and spectrometry, can have in the analysis of TSD, with notable sensitivity and specificity. This paper also analyzes the intrinsic and extrinsic limits of these models and emphasizes the need to continue research work on this topic, considering the importance that this parameter can assume in forensic investigations against a suspect.

Detection of invisible biological traces in relation to the physicochemical properties of substrates surfaces in forensic casework

Touch DNA, which can be found at crime scenes, consists of invisible biological traces deposited through a person's skin's contact with an object or another person. Many factors influence touch DNA transfer, including the "destination" substrate's surface. The latter's physicochemical characteristics (wettability, roughness, surface energy, etc.) will impact touch DNA deposition and persistence on a substrate. We selected a representative panel of substrates from objects found at crime scenes (glass, polystyrene, tiles, raw wood, etc.) to investigate the impact of these characteristics on touch DNA deposition and detection. These were shown to impact cell deposition, morphology, retention, and subsequent touch DNA genetic analysis. Interestingly, cell-derived fragments found within keratinocyte cells and fingermarks using in vitro touch DNA models could be successfully detected whichever the substrates' physicochemistry by targeting cellular proteins and carbohydrates for two months, indoors and outdoors. However, swabbing and genetic analyses of such mock traces from different substrates produced informative profiles mainly for substrates with the highest surface free energy and therefore the most hydrophilic. The substrates' intrinsic characteristics need to be considered to better understand both the transfer and persistence of biological traces, as well as their detection and collection, which require an appropriate methodology and sampling device to get informative genetic profiles.

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.

Enzyme activity, DNA degradation and drying times of semen, saliva and vaginal material

The stability of enzyme activity and the amount of detectable DNA within liquid samples of semen, saliva and vaginal material were tested across a number of days. The concentration of DNA within neat semen and saliva samples fell significantly after one week of refrigeration. No apparent change in acid phosphatase or amylase enzyme activity was observed in neat semen and saliva samples over 96 or 72 h respectively. Changes in the enzyme activity of most of the dilute semen and saliva samples, as well as the neat vaginal material sample, were noted after 24 h. The drying times and sizes of stains produced from various volumes of neat semen, saliva and vaginal material were tested on porous and non-porous surfaces at room temperature. Larger volumes of body fluid took longer to dry and generally resulted in larger stains. Body fluids on a non-porous surface took longer to dry than on the porous surface tested.

Nucleic Acids Persistence-Benefits and Limitations in Forensic Genetics

The analysis of genetic material may be the only way to identify an unknown person or solve a criminal case. Often, the conditions in which the genetic material was found determine the choice of the analytical method. Hence, it is extremely important to understand the influence of various factors, both external and internal, on genetic material. The review presents information on DNA and RNA persistence, depending on the chemical and physical factors affecting the genetic material integrity. One of the factors taken into account is the time elapsing to genetic material recovery. Temperature can both preserve the genetic material or lead to its rapid degradation. Radiation, aquatic environments, and various types of chemical and physical factors also affect the genetic material quality. The substances used during the forensic process, i.e., for biological trace visualization or maceration, are also discussed. Proper analysis of genetic material degradation can help determine the post-mortem interval (PMI) or time since deposition (TsD), which may play a key role in criminal cases.

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.

Improvements, factors, and influences on DNA recovery from firearms

Touch DNA recovery from firearms can be central to many criminal investigations, yet the generation of DNA profiles from these items remains poor. Currently in Australia, published casework data highlights extremely poor DNA success from samples recovered from firearms. Only between 5% and 25% of samples result in useful DNA data and therefore increasing the success of DNA recovered from firearms is highly important but has not yet been explored in-depth. This study focused on increasing the recovery of DNA from ten firearm components that were held for 15 s. Multiple recovery methods were used, and the resulting genetic data compared. DNA evidence may be deliberately removed from firearms after discharge to hamper forensic investigations, therefore this study examined the effect of wiping down the components or handling them with gloves. A standard double swab and rinse swab recovery method resulted in an average of 73% cellular recovery. A cumulative swab process had the highest average recovery at 86%, although it was found that increasing the DNA yield led to an increase in mixture complexity. Wiping over the components was observed to remove on average 69% of cellular material, compared with 33% when handed with gloves. However, the size and texture of the components affected the efficiency of cellular material removal. The results from this study allow for prioritisation of areas to sample on firearms, as well as suggesting techniques that can be applied for the optimum process of cellular recovery and subsequent generation of STR DNA data.

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.

"Touch microbiome" as a potential tool for forensic investigation: A pilot study

Human skin hosts a variety of microbes that can be transferred to surfaces ("touch microbiome"). These microorganisms can be considered as forensic markers similarly to "touch DNA". With this pilot study, we wanted to evaluate the transferability and persistence of the "touch microbiome" on a surface after the deposition of a fingerprint and its exposure for 30 days at room temperature. Eleven volunteers were enrolled in the study. Skin microbiome samples were collected by swabbing the palm of their hands; additionally, donors were asked to touch a glass microscope slide to deposit their fingerprints, that were then swabbed. Both human and microbial DNA was isolated and quantified. Amelogenin locus and 16 human STRs were amplified, whereas the V4 region of 16 S rRNA gene was sequenced using Illumina MiSeq platform. STR profiles were successfully typed for 5 out of 22 "touch DNA" samples, while a microbiome profile was obtained for 20 out of 22 "touch microbiome" samples. Six skin core microbiome taxa were identified, as well as unique donor characterizing taxa. These unique taxa may have relevance for personal identification studies and may be useful to provide forensic intelligence information also when "touch DNA" fails. Additional future studies including greater datasets, additional time points and a greater number of surfaces may clarify the applicability of "touch microbiome" studies to real forensic contexts.

Corneocyte lysis and fragmented DNA considerations for the cellular component of forensic touch DNA

DNA deposited by individuals' hands is a routine part of forensic analysis, yet little is understood about the precise cellular contents left by handling. "Dead" skin cells known as corneocytes make up the majority of the cellular material left in touch deposits by people's hands but are known to lack nuclei, making their DNA content ambiguous. Here we measure DNA released from anucleate corneocytes following various lysis methods to determine how much DNA may be present in these cells and how best to recover it from inside the cornified envelope. We demonstrate that enhanced lysis methods using a reducing agent and longer incubation may be valuable for hand deposit samples. Corneocyte DNA can be characterized as highly degraded based on the quantification, STR profiling and fluorescence microscopy of the cells from freshly washed hands. Purification to target shorter DNA fragments is demonstrated. DNA from the washed corneocyte cells is shown to constitute the majority of recoverable DNA with these methods. We consider the use of new methods adapted to cornified cells and fragmented DNA for future research into this sample type.

Exploration of cell-free DNA (cfDNA) recovery for touch deposits

Although touch deposit DNA is widely used in forensic casework, its cellular and acellular contents and their biological origins are poorly understood. There is evidence that the cell-free component of DNA deposited by handling may contribute substantial genetic information; however, most research into touch DNA recovery does not separate cellular and cell-free fractions or seek to characterize their contents. This work is an important early step in developing methods to isolate the cfDNA from biological material deposited by handling. Size-filtration as a separation technique was determined to be prone to DNA loss, even on optimized control samples of pure ladder DNA. Centrifugal separation was optimized to determine minimum speed and time required to reliably remove all cellular debris from the material collected by rinsing donor hands. To determine if the centrifugal force risked rupturing shed corneocyte cells and releasing cellular DNA into the supernatant, DNA levels were measured, and cells were visualized microscopically before and after centrifugation of hand rinses. Heated buccal cells were used as a positive control to demonstrate cell rupture would be detected with these methods. Following the determination of a suitable separation technique, an investigation into purification methods for cfDNA was conducted. DNA recovery using three kits for plasma cfDNA, one for PCR clean-up and one for genomic DNA were assessed on both ladder DNA to simulate cfDNA fragments and on collected hand deposit supernatants from both unwashed and washed hands. Purification methods designed for recovery of short DNA fragments from plasma yielded the highest recovery percentage across sample types, with BioChain cfPure performing the best. Donors' hands were shown to shed high levels of cfDNA, which were better recovered with a method for short fragments than with a traditional genomic technique often used on touch DNA samples.

Forensic DNA Profiling: Autosomal Short Tandem Repeat as a Prominent Marker in Crime Investigation

Short tandem repeat (STR) typing continues to be the primary workhorse in forensic DNA profiling. Therefore, the present review discusses the prominent role of STR marker in criminal justice system. All over the world, deoxyribonucleic acid (DNA) profiling provides evidence that may be used to convict criminals, as an irrefutable proof of wrongful convictions, invaluable links to the actual perpetrators of crimes, and could also deter some offenders from committing more serious offences. Clearly, DNA profiling tools have also aided forensic scientists to re-evaluate old cases that were considered closed as a result of inadequate evidence. In carrying out this review, a comprehensive electronic literature search using PubMed, ScienceDirect, Google Scholar and Google Search were used, and all works meeting the subject matter were considered, including reviews, retrospective studies, observational studies and original articles. Case reports presented here, further demonstrates the crucial role of forensic DNA profiling in mitigating and providing compelling evidence for the resolution of crimes. For case report 1, there was a 100% match between the DNA recovered from the items found in the crime scene, and the suspect's DNA sample collected via buccal swab following 15 STR loci examination. Case report 2 further highlights the indispensable contribution of DNA database in solving crime. Therefore, it has become very necessary for developing countries like Nigeria to develop a national DNA database and make policies and legislatures that will further expand and enable the practice of forensic genetics, particularly DNA profiling.

An efficient and eco-friendly workflow for dual fingermark processing and STR profiling

Since its discovery in 1997, DNA retrieved from touched or handled items (touch DNA) has been increasingly used in criminal casework. Depending on the nature of the substrate examined, numerous techniques are being used for fingermark (FM) collection and development, however, it has been shown that FM processing may impede or even prevent the dual analysis of FMs and DNA. In search for a possible solution, we have recently established a novel workflow for a non-destructive collection and eco-friendly visualization of latent FMs using white BVDA gel-lifters and black Wetwop® solution. In the present study, the scope and limitations of the proposed protocol were thoroughly examined for DNA recovery and genotyping in relation to substrate type (porous and non-porous), time elapsed after the deposition (1, 7 and 14 days) and donor's gender. The study included 120 developed FMs of 20 donors (10 males and 10 females, aged 25-50 years), from which 240 DNA samples were recovered and quantified. The independent analysis of two DNA samples recovered from each FM, one - from the adhesive surface of the gel-lifter and the other - from its imprint on the protecting acetate cover, allowed us not only to increase the total number of the identified donors, but also to achieve a higher level of confidence per FM. Though this approach appeared to be more efficient on non-porous substrates (up to 65% on car tin), it is noteworthy that forensically useful DNA profiles (with at least 8 full STR loci) were generated from poor-quality FMs on the porous substrate, drywall (25% and 15% in males and females, respectively). Finally, the integration of the results of touch DNA analysis and that of FM visual inspection allowed us to increase by more than half the number of personal identifications and to strengthen the chain of forensic evidence.

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.

Detection of latent fingermarks and cells on paper

Fingermarks and DNA are valuable traces in forensic investigations potentially allowing for the identification of the source of the trace or highlighting a link between a touched object and an individual. These traces are often latent and need to be detected before recovery. While a number of validated methods exist for fingermark detection, no routine method is in place for the detection of DNA. This study investigates the use of pdimethylaminobenzaldehyde (DMAB) in conjunction with indanedione zinc (IND-Zn) for the detection of latent cellular material and fingermarks on paper. The aim of this proof-of-concept study is to determine the successfulness of this reagent (DMAB-IND) in the detection of the respective traces and observe the impact it has on the resulting DNA profile. It was found that latent fingermarks and the associated cells could be visualised following treatment with the reagent. Samples treated with DMAB-IND showed a significantly higher percentage of alleles called compared to IND-Zn-treated and untreated samples due to the targeted recovery of cells. However, the reagent appears to degrade DNA at a rapid rate, requiring the treated samples to be processed for DNA on the day of treatment.

Data driven optimization of sexual assault case processing

In recent years, several forensic laboratories have noted an increase in the number of sexual assault cases submitted for testing, often leading to longer turnaround times. In that context, forensic laboratories may be interested in reviewing their procedures to increase productivity. Here, we present two different strategies that were put in place in our laboratory. First, we changed the way sexual assault evidence kits (SAEK) are processed by implementing an optimized workflow that prioritizes the internal samples (vaginal, anal, and oral). This new procedure allowed for a drastic decrease in turnaround time, while maintaining a similar investigative power.

Secondly, we used data from casework to target cases and samples that were likely to yield biological material from the perpetrator, in an attempt to avoid dedicating time and effort to cases for which there is a very low probability of obtaining foreign DNA evidence. Among other things, we looked at the likelihood of obtaining DNA from the perpetrator when the complainant reported the use of a condom, has showered after the assault or when the complainant has no memory of the assault. Results show that those circumstances do not dramatically decrease the probability of finding DNA from the perpetrator.

Investigation of direct and indirect transfer of microbiomes between individuals

The human microbiome encompasses the fungi, bacteria and viruses that live on, within, and immediately surrounding the body. Microbiomes have potential utility in forensic science as an evidentiary tool to link or exclude persons of interest associated with criminal activities. Research has shown the microbiome is individualised, and that personal microbial signatures can be recovered from surfaces such as phones, shoes and fabrics. Before the human microbiome may be used as an investigative tool, further research is required to investigate the utility and potential limitations surrounding microbial profiling. This includes the detectability of microbial transfer between individuals or items, the associated risks (such as contamination events) and the applicability of microbial profiling for forensic purposes. This research aimed to identify whether an individual's distinguishable microbiome could be transferred to another individual and onto substrates, and vice versa. Paper, cotton, and glass surfaces were chosen to represent a range of substrate matrices. The study involved six participants placed into three pairs; participants took part in two modes of transfer. Transfer Mode 1 involved the pair shaking hands, followed by rubbing a substrate in their right hand. Transfer Mode 2 involved individuals rubbing a substrate in their left hand, swapping substrates with their partner and then rubbing the swapped substrate in their left hand. 16S rRNA sequencing was performed on the extracted microbial DNA from participant and substrate samples. Quantitative Insights into Microbial Ecology 2 (QIIME 2) was used for sequence quality control and beta (between-sample) diversity analyses and taxonomic assignment. Principal Coordinate Analysis (PCoA) based on Jaccard distances was visualised through Emperor software to determine the phylogenetic similarity of bacterial communities between participants and among participant pairs. Statistical testing through PERMANOVA revealed significant differences in the Jaccard distances between each participant pair (P < 0.001), highlighting not only the potential distinguishability of skin microbiomes among individuals, but also the clustering effect observed between participant pairs due to the potential transfer of hand-associated microbiomes between individuals. The study demonstrated that transfer of the human skin microbiome had occurred between all participant pairs, regardless of substrate type or mode of transfer.

Bayesian networks and dissonant items of evidence: A case study

The assessment of different items of evidence is a challenging process in forensic science, particularly when the relevant elements support different inferential directions. In this study, a model is developed to assess the joint probative value of three different analyses related to some biological material retrieved on an object of interest in a criminal case. The study shows the ability of probabilistic graphical models, say Bayesian networks, to deal with complex situations, those that one expects to face in real cases. The results obtained by the model show the importance of a conflict measure as an indication of inconsistencies in the model itself. A contamination event alleged by the defense is also introduced in the model to explain and solve the conflict. The study aims to give an insight in the application of a probabilistic model to real criminal cases.

Persistence of DNA in the Singapore context

The relevance and not merely the presence of one's DNA at a crime scene has become the emerging issue in courtrooms all over the world today. By studying the length of time DNA is likely to persist in an environment until detection, a more holistic assessment of DNA evidence in the context of a case can be made. The current study looks at the persistence of DNA from blood, keratinocytes, and several types of mock exhibits under various conditions, in the tropical rainforest climate of Singapore. While DNA on articles left outdoors showed highly variable persistence subject to the presence of rainfall, DNA from items placed indoors at ambient temperature and under controlled temperature and humidity is comparatively stable. The information gathered from this study, while not exhaustive, serves to provide investigators and the courts with a better understanding of the relevance of DNA recovered from crime scenes of different environmental conditions.

Unintentional effects of cleaning a crime scene-when the sponge becomes an accomplice in DNA transfer

DNA transfer in aqueous solutions as well as the persistence of DNA on washed items has become a major subject of research in recent years and is often a significant problem in court. Despite these approaches, the question about the "mobility" of DNA especially in capital offenses cannot be answered in every case, since a variety of scenarios for DNA transfer are possible. The aim of this study was to investigate whether DNA traces could be distributed by cleaning an object. For this purpose, a large table surface and fabric piece were artificially provided with skin contact traces and body fluids (saliva and blood) in two series of experiments and then wiped off with water or with soap water (218 samples in total). These experiments resulted in a clear "carry over" of DNA traces especially for body fluid samples (100% of blood samples and 75% of saliva samples led to a complete profile). The results could be confirmed in a second experimental set-up with 384 samples using different cleaning agents and more intense cleaning actions. Even small amounts of 5-10 μl body fluid led to complete profiles in around 45% of the samples, while 20 μl led to nearly 65% complete profiles. A strong impact of the amount of traces and the chosen surface could be demonstrated, while the active component of the cleaning agent seemed to be of less influence with the explicit exception of chloric agents which rendered almost everything completely DNA-free. In summary, a distribution of DNA traces by wiping or scrubbing an object could be clearly proven.

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.

Single source DNA profile recovery from single cells isolated from skin and fabric from touch DNA mixtures in mock physical assaults

The ability to obtain DNA profiles from trace biological evidence is routinely demonstrated with so-called 'touch DNA evidence', which is generally perceived to be the result of DNA obtained from shed skin cells transferred from a donor's hands to an object or person during direct physical contact. Current methods for the recovery of trace DNA employ swabs or adhesive tape to sample an area of interest. While of practical utility, such 'blind-swabbing' approaches will necessarily co-sample cellular material from the different individuals whose cells are present on the item, even though the individuals' cells are principally located in topographically dispersed, but distinct, locations on the item. Thus the act of swabbing itself artifactually creates some of the DNA mixtures encountered in touch DNA samples. In some instances involving transient contact between an assailant and victim, the victim's DNA may be found in such significant excess as to preclude the detection and typing of the perpetrator's DNA. In order to circumvent the challenges with standard recovery and analysis methods for touch DNA evidence, we reported previously the development of a 'smart analysis' single cell recovery and DNA analysis method that results in enhanced genetic analysis of touch DNA evidence. Here we use the smart single cell analysis method to recover probative single source profiles from individual and agglomerated cells from various touched objects and clothing items belonging to known donors. We then use the same approach for the detection of single source male donor DNA in simulated physical contact/assault mixture samples (i.e. male 'assailant' grabbing the wrist, neck or clothing from the female 'victim', or being in transient contact with bedding from the 'victim'). DNA profiles attributable to the male or female known donors were obtained from 31% and 35% of the single and agglomerated bio-particles (putative cells) tested. The known male donor 'assailant' DNA profile was identified in the cell sampling from every mixture type tested. The results of this work demonstrate the efficacy of an alternative strategy to recover single source perpetrator DNA profiles in physical contact/assault cases involving trace perpetrator/victim cellular admixtures.

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

The detection of DNA of a certain person on the inside of a piece of clothing involved in a crime scene is usually seen as confirmation that this person is the owner or bearer and therefore participated in this crime. However, besides the possibilities of secondary or even tertiary transfer of DNA, the accused often argues that he lent the garment to another person who by chance did not leave any DNA while committing the crime. Then, forensic genetic scientists have to answer the question how long DNA persists on an item used in daily routine and how long a piece of clothing must be worn to definitively leave detectable DNA behind. In an attempt to answer these questions, several scenarios with two or three individuals wearing the same sweatband for different time periods were set up. DNA left on the sweatbands was isolated, quantified, and then analyzed using the Powerplex® ESX17fast kit. The majority of samples displayed all alleles of both/all three wearers on the outside (67%) as well as on the inside (80%) of the sweatbands. In contrast, a single profile of the first wearer could only be found once among all 204 samples, a single profile of the second wearer in 7% of samples. Wearing the sweatband for only 10 min was enough to result in a complete profile of the second wearer in 79% of samples. So, it is highly unlikely to wear/use a piece of clothing for even a short period of time without leaving own DNA behind.

Persistence of DNA on clothes after exposure to water for different time periods-a study on bathtub, pond, and river

DNA traces on clothes of drowned bodies can provide important evidence for police investigations, especially in cases of suspected suicides or homicides. However, it is generally assumed that the water "erodes" a large part of the DNA depending especially on the exposure time. In forensic casework, DNA of suspects could be found frequently on clothes of drowned bodies after hours, sometimes days of exposure to water. This study was conducted to attempt a general statement about the conditions under which sufficient DNA remains can be expected for molecular genetic analysis. For this purpose, different scenarios were designed including DNA from three to five people, different types of waters (tap, pond, bathtub and river) for various time periods, with higher water pressure, different temperature, and soapy water (bathtub). Epithelial cells and blood cells were mounted on cotton cloths, and the DNA left after exposure was analyzed using the Powerplex® ESX17fast kit. In the indoor experiments, complete profiles could be seen even after 10 min rinsing of clothes under the tap and after 1 week in the bathtub. Outdoors, the results differed considerably between summer and winter as well as between pond and river. The longest exposure time still resulting in a complete profile was 2 weeks for a sample with skin cells in the pond during winter. In summer, the time period for erasing the bulk of DNA was 4 hours regarding epithelial samples and more than 1 day for blood samples in pond and river environments. All in all, the results demonstrate that DNA could still be recovered from clothes exposed to water for more than 1 week.

Comparison of preprocessing methods and storage times for touch DNA samples

Aim

To select appropriate preprocessing methods for different substrates by comparing the effects of four different preprocessing methods on touch DNA samples and to determine the effect of various storage times on the results of touch DNA sample analysis.

Method

Hand touch DNA samples were used to investigate the detection and inspection results of DNA on different substrates. Four preprocessing methods, including the direct cutting method, stubbing procedure, double swab technique, and vacuum cleaner method, were used in this study. DNA was extracted from mock samples with four different preprocessing methods. The best preprocess protocol determined from the study was further used to compare performance after various storage times. DNA extracted from all samples was quantified and amplified using standard procedures.

Results

The amounts of DNA and the number of alleles detected on the porous substrates were greater than those on the non-porous substrates. The performances of the four preprocessing methods varied with different substrates. The direct cutting method displayed advantages for porous substrates, and the vacuum cleaner method was advantageous for non-porous substrates. No significant degradation trend was observed as the storage times increased.

Conclusion

Different substrates require the use of different preprocessing method in order to obtain the highest DNA amount and allele number from touch DNA samples. This study provides a theoretical basis for explorations of touch DNA samples and may be used as a reference when dealing with touch DNA samples in case work.