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

Hungarian legislation regarding implementing a forensic DNA elimination database

The inception of forensic DNA elimination database represents a pivotal advancement in forensic science, aiming to streamline the process of distinguishing between DNA found at crime scenes and that of individuals involved in the investigation process, such as law enforcement personnel and forensic lab staff. In subsequent phases, once familiarity with the database is achieved by its administrators and other stakeholders, and they have accrued sufficient experience, the possibility of expanding the database to encompass first responders-including firefighters, paramedics, emergency medical technicians, and other emergency services personnel-can be contemplated. Key challenges in managing these databases encompass the grounds for collecting samples, ensuring the integrity of both samples and profiles, along with the duration of retention, access to the database, and the protocols to follow when a match is found in the database. This paper outlines the conceptual and detailed legislative framework in Hungary, where the forensic DNA elimination database was introduced in 2022.

Saliva-derived secondary DNA transfer on fabric: The impact of varying conditions

This study explored secondary DNA transfer involving saliva, a body fluid often encountered in forensic investigations. Various factors were examined to investigate their potential impact on the transfer of DNA from saliva stains deposited onto common types of fabric (cotton, nylon, and towel). We examined varying types of saliva moisture (wet, dry, and rehydrated) and different types of contact (controlled pressure and active/friction pressure) to quantitatively evaluate how such variables could impact transfer and possible conclusions surrounding saliva-derived DNA deposits. The transfer of DNA was generally least pronounced with more absorbent primary fabrics (cotton and towel materials) while a less absorbent primary fabric (nylon) exhibited a greater propensity for DNA transfer. There were significantly higher amounts of transferred DNA (p < 0.05) observed in wet saliva samples compared to dry and rehydrated saliva samples. Further, the use of active pressure (friction) appeared to result in more DNA transfer overall as compared to controlled pressure contact. Experiments conducted with wet saliva and active pressure (friction) demonstrated the highest likelihood of transfer, with the primary nylon and secondary towel fabric combination demonstrating the greatest average transfer percentage of 94.74 %. The variables explored in this study presented multiple combinations wherein a sufficient amount of DNA (≥ 240 pg total) was transferred to the secondary fabric, making it potentially suitable for STR-PCR amplification in our laboratory. The findings from this study indicate that the type of primary fabric receiving the saliva deposit, the type of saliva moisture, the type of secondary fabric and its moisture type, and the type of contact all have the potential to affect the quantity of DNA transferred and recovered. This study provides empirical data on the ease, and to what extent, DNA from saliva transfers between fabrics and aids DNA activity level evaluations. The significance of this research lies in its contribution to expanding our current understanding of DNA transfer involving saliva within forensic science and criminal investigations.

Assessing the consistency of shedder status under various experimental conditions

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

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.

Secondary and tertiary transfer of latent fingermarks using a sticky note - A feasibility study

Latent fingermarks are enhanced in order to be visible and available for comparison to determine source. Once a fingermark has been identified to a source, the activity that led to it being left on a particular surface may need to be determined. It has been previously shown that under certain conditions fingermarks initially deposited onto a surface (the primary transfer) can be transferred on to another substrate through direct contact - secondary transfer. This study investigates the possibility of secondary and subsequent tertiary transfer using sticky notes. To explore secondary transfer, fingermarks were deposited directly onto two different brands of sticky notes, spanning the adhesive and non-adhesive areas, and then placed in direct contact with paper for up to 72 h under a 5 kg weight. For some donors, there was transfer of fingermarks from the sticky note to the paper, with better results for the adhesive areas. The quality of the transferred fingermarks was dependent on initial fingermark quality and the transferred fingermark was a mirror image of the original. The type of paper used as the secondary substrate was also shown to have an effect. Given the adhesive nature of sticky notes tertiary transfer was also investigated and the potential to lift fingermarks from a glass slide and transfer them onto paper or a second glass slide. In the case of transfer to paper, there were only tertiary transferred fingermarks considered to be of useful quality (score 3 or 4) in 6% of samples and a further 33% of samples were detected but provided evidence of contact only (score 1 or 2) (n = 120). For transfer to glass, tertiary transferred samples were of poorer quality with no useful fingermarks and only 3% of samples scoring 1 or 2 (n = 120). The latter was in part due to the deposition of sticky note adhesive traces obscuring the fingermarks. In the case of tertiary transfer, fingermarks on the final tertiary surface were in the correct orientation. This work demonstrates that whilst tertiary transfer of fingermarks is possible under the laboratory conditions used, the likelihood of the effective transfer of a useful and potentially identifiable fingermark is in reality low.

Indirect DNA Transfer and Forensic Implications: A Literature Review

Progress in DNA profiling techniques has made it possible to detect even the minimum amount of DNA at a crime scene (i.e., a complete DNA profile can be produced using as little as 100 pg of DNA, equivalent to only 15-20 human cells), leading to new defense strategies. While the evidence of a DNA trace is seldom challenged in court by a defendant's legal team, concerns are often raised about how the DNA was transferred to the location of the crime. This review aims to provide an up-to-date overview of the experimental work carried out focusing on indirect DNA transfer, analyzing each selected paper, the experimental method, the sampling technique, the extraction protocol, and the main results. Scopus and Web of Science databases were used as the search engines, including 49 papers. Based on the results of this review, one of the factors that influence secondary transfer is the amount of DNA shed by different individuals. Another factor is the type and duration of contact between individuals or objects (generally, more intimate or prolonged contact results in more DNA transfer). A third factor is the nature and quality of the DNA source. However, there are exceptions and variations depending on individual characteristics and environmental conditions. Considering that secondary transfer depends on multiple factors that interact with each other in unpredictable ways, it should be considered a complex and dynamic phenomenon that can affect forensic investigation in various ways, for example, placing a subject at a crime scene who has never been there. Correct methods and protocols are required to detect and prevent secondary transfer from compromising forensic evidence, as well as the correct interpretation through Bayesian networks. In this context, the definition of well-designed experimental studies combined with the use of new forensic techniques could improve our knowledge in this challenging field, reinforcing the value of DNA evidence in criminal trials.

A collection of idioms for modeling activity level evaluations in forensic science

This paper presents a collection of idioms that is useful for modeling activity level evaluations in forensic science using Bayesian networks. The idioms are categorized into five groups: cause-consequence idioms, narrative idioms, synthesis idioms, hypothesis-conditioning idioms, and evidence-conditioning idioms. Each category represents a specific modeling objective. Furthermore, we support the use of an idiom-based approach and emphasize the relevance of our collection by combining several of the presented idioms to create a more comprehensive template model. This model can be used in cases involving transfer evidence and disputes over the actor and/or activity. Additionally, we cite literature that employs idioms in template models or case-specific models, providing the reader with examples of their use in forensic casework.