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.

Showcasing water-based delivery of an amino acid targeting fingermark developer in a hydrogel.

Most recommended methods for visualising fingermarks on paper rely on chemical developers that target and react with amino acids. Traditionally, these developers are sprayed onto paper substrates in solutions of per- and polyfluoroalkyl substances (PFAS), but now those same PFAS chemicals are undergoing phaseout or phasedown, which threatens to undermine forensic capabilities. This situation provides an opportunity to pivot towards greener approaches to fingermark visualisation. The ideal methodology would be a water-based treatment, as these provide superior safety for practitioners, combined with environmental sustainability. A major hurdle to implementing a water-based fingermark developer targeting amino acids is that water, as a universal solvent, can dissolve the eccrine components in fingermarks, as well as any optical or luminescent dyes that are created, causing the ridge detail to run or dissolve. This work circumvents this problem by delivering the amino acid developer alloxan in a hydrogel, which enables sharp fingermark ridge details to be observed despite it being a water-based treatment. Alloxan dissolved in a viscous hydrogel is shown here to react with the amino acids in fingerprint residues to form the coloured dye murexide, supported by optimisation and characterisation studies.

ENFSI 2022 multidisciplinary collaborative exercise: organisation and outcomes.

The use of collaborative exercises (CE) and proficiency tests (PT) as part of the governance programme for any forensic science laboratory has become commonplace and recommended by several international organisations. Traditionally these have been discipline-specific exercises testing a laboratory's ability in a single area of forensic science. However, the "real" world is normally more complex and, in many instances, forensic material must be examined for a number of different evidence types. This article summarises the concepts, planning, design, preparation, implementation, co-ordination and evaluation of the 2022 Multidisciplinary Collaborative Exercise (2022-MdCE) covering a range of forensic disciplines, specifically DNA, fingerprint, documents and handwriting. The exercise consisted of a questioned letter with typescript text and a signature. In addition, the letter contained a visible bloody fingermark in the area of the signature, a visible staining in the lower left-hand corner, a latent fingermark and an indented impression. The analysis of the results showed that, in the investigation of the bloody fingermark, the priority was given to the DNA examination. Some critical issues emerged in relation to the biological (DNA)/ink sampling strategies when applied before fingermark visualisation. Another outcome of the exercise has been to demonstrate the importance of indented impressions, which have been underestimated by a significant number of participants. As setters, more in-depth studies are needed to produce consistent samples. This concerns all the disciplined involved but especially DNA and fingermarks. Based on this exercise, it is believed that this approach to testing of forensic disciplines allows the analysis of good practice within the various scientific areas, as well as scrutinising the process and sequence of events for examining the material within a forensic laboratory in the best conservative way for all kind of evidences.

Application of mist to fingermark detection: Misting with high-boiling-point liquid containing p-dimethylaminocinnamaldehyde and cyanoacrylate.

In order to detect latent fingerprints that could be damaged by liquid or powder reagents, non-destructive processes such as gaseous reagents have been developed. In this report, we propose the use of fine mist generated when hot vapor of high-boiling-point liquids is rapidly cooled by surrounding air for fingermark detection. Octyl acetate (OA), 2-phenoxyethanol (2PE), and methyl decanoate (MD) were found to efficiently produce mist when heated to 230°C. By combining these liquids with p-dimethylaminocinnamaldehyde (DMAC) and cyanoacrylate (CN), our team demonstrated effective fluorescence staining of cyano-treated fingermarks using DMAC/OA misting or DMAC/2PE misting, and one-step fluorescence detection of latent fingermarks without cyanoacrylate treatment using DMAC/OA/CN misting or DMAC/MD/CN misting. Fingermark fluorescence was efficiently observed by excitation with a blue LED light (max. wavelength 470 nm) equipped with an interference filter and passing through a 520 nm long-pass filter. We successfully obtained fluorescent images from fingermarks on several substrate materials using the developed misting method.

Fingermarks in wildlife forensics: A review.

Wildlife forensics is defined as providing forensic evidence to support legal investigations involving wildlife crime, such as the trafficking and poaching of animals and/ or their goods. While wildlife forensics is an underexplored field of science, the ramifications of poaching can be catastrophic. The consequences of wildlife crime include disease spread, species and habitat loss, human injury, and cultural loss. Efforts to use forensic science to combat poaching are currently limited to DNA-based techniques. However, fingermark analysis for the identification of perpetrators of wildlife crimes has not been explored to the same extent, despite being a cost-effective, simple-to-use forensic method that is easy to deploy in-field. This review covers literature that has explored fingermark examination techniques used on wildlife-related samples, such as pangolin scales, ivory-based substances, bone, and eggs, as well as feathers and skins, among more obscure trafficked items. Useful preliminary work has been conducted in this subject area, demonstrating that commonly used fingermark analysis techniques can be applied to wildlife-based items. However, many of these studies suffer from limitations in terms of experimental design. More work should be done on creating studies with larger sample sizes and novel approaches should be validated under environmental conditions that mimic real crime scenes. Further research into determining the forensic fingermark analysis techniques that perform the most efficiently in the environmental conditions of the countries where they are needed would therefore benefit legal investigations and help to reduce instances of poaching.

Preliminary Study: DNA Transfer and Persistence on Non-Porous Surfaces Submerged in Spring Water.

Submerged items are often thought to lack evidentiary value. However, previous studies have shown the ability to recover DNA from submerged porous items for upwards of six weeks. The crevices or interweaving fibers in porous items are thought to protect DNA from being washed away. It is hypothesized that, because non-porous surfaces do not have the same traits that might aid in DNA retention, then DNA quantities and the number of donor alleles recovered would decrease over longer submersion periods. Additionally, it is hypothesized that DNA quantity and the number of alleles would be negatively affected by flow conditions. Neat saliva of known DNA quantity was applied to glass slides and exposed to stagnant and flowing spring water to observe the effects on both DNA quantity and STR detection. Results supported that DNA deposited onto glass and subsequently submerged in water experienced a decrease in DNA quantity over time, yet submersion did not have as strong of a negative effect on the detected amplification product. Additionally, an increase in DNA quantity and detected amplification product from designated blank slides (no initial DNA added) could indicate the possibility of DNA transfer.

Can latent fingerprint disclose the sex of the donor? A preliminary test study using GC-MS analysis of latent fingerprints.

While fingerprints are a highly used means of identification, not every fingerprint left behind on a potential crime scene can be used for identification purposes. In some cases, the fingerprint may be smudged, partially preserved or overlapping with other prints hence distorting the ridge pattern and may therefore be not appropriate for identification. Further, fingermark residue yields a very low abundance of genetic material for DNA analysis. In such cases, the fingermark may be used to retrieve basic donor information such as sex. The focus of this paper was to assess the possibility of differentiating between the sexes of the donor of latent fingermarks. Analytical method was GC-MS analysis of the chemical compounds of latent fingermarks using 22 male and 22 female donors. Results showed 44 identified compounds. Two alcohols, octadecanol C18 and eicosanol C20 , were found to show a difference that was statistically significant between male and female donors. There is also some evidence for the possibility of distinguishing sex of the fingermark donor based on the distribution of branched chain fatty acids, as free compounds or esterified in wax esters.

Comparison of carbon and iron oxide based powder suspension formulations.

Powder suspensions (PS) are a fingermark development technique made up of a mixture of an insoluble powder and surfactant solution. In the UK, carbon-based PS is used operationally on adhesive surfaces while iron oxide-based PS is used on flexible plastics. In NSW, Australia, only carbon-based suspensions are used due to a lack of research using iron oxide PS in an Australian context. In this research, a range of iron oxide powders and surfactant types were tested to optimise two iron oxide formulations. General observations found that thinner suspensions improved the ease of use in this technique while slightly improving the quality of developed fingermarks. The first optimised formulation involved a magnetic iron-oxide from Fisher Scientific mixed with a dilute Triton X-100 surfactant, and the other an iron-oxide nanopowder from Sigma Aldrich mixed with a 4% Tween 20 solution. The two formulations were then compared with a pre-mixed carbon-based PS, Wet Powder. This comparison showed that the effectiveness of each formulation is heavily dependent on substrate type. Both formulations had issues with heavy background staining on different kinds of surfaces. However, Wet Powder was shown to be the most consistently effective fingermark detection technique overall, especially on adhesive tapes. Despite this, iron-oxide PS were still a highly effective fingermark development technique, notably on plastic surfaces.

Error rates and proficiency tests in the fingerprint domain: A matter of perspective and conceptualization.

The purpose of this work is to critically analyse the aspects connected both with the measurement of error rates and with the design of proficiency tests and collaborative exercises in the fingerprint domain. All from the dual perspective of practitioners and organizers of PT's/CE's. A thorough analysis of the types of errors, of the methods to infer them through black-box studies and PT's/CE's is carried out, and the limits to the generalization of error rates are described, providing insightful indication on how to design PT's/CE's in the fingerprint domain, which are aimed to represent the complexity of casework.

National fingermark visualisation collaborative exercise 2020.

In 2020, the Defence Science and Technology Laboratory organised and ran what is believed to be the first UK national collaborative exercise of its kind in the field of fingermark visualisation, on behalf of the Forensic Science Regulator. Laboratories were provided with a piece of wrapping paper, a challenging item for fingermark visualisation due to its semi-porous characteristics, both from a planning and processing perspective, and asked to treat it as a major crime exhibit. Due to the complexity of the substrate, variation in approach was anticipated. 23 laboratories from 21 organisations completed the exercise. In general, laboratories performed well, providing assurance to the Forensic Science Regulator regarding their ability to visualise fingermarks. Key learning points were identified around decision-making, planning and implementation of fingermark visualisation processes - all of which assist in raising the level of understanding around the likely success of fingermark visualisation. Lessons learnt, along with the overall findings, were shared and discussed in a workshop held in summer 2021. The exercise provided a useful insight into the current operational practices of participating laboratories. Areas of good practice were identified as well as the areas within the laboratories' approach that could be altered or adapted.

MALDI MSI Separation of Same Donor's Fingermarks Based on Time of Deposition-A Proof-of-Concept Study.

Despite the advent of DNA profiling, fingerprints still play an important role in suspect identification. However, if single crime scene marks may be challenging to identify, overlapping fingermarks, understandably, pose an even greater challenge. In the last decade, mass spectrometry-imaging methods have provided a possible solution to the separation of fingermarks from two or more donors, based on the differential chemical composition. However, there are no studies attempting to separate overlapping marks from the same donor. This is important in relation to fingermark deposition at different times, which could be critical, for example, to ascertain legitimate access to the scene. In the work presented here, we investigate whether Matrix-Assisted Laser Desorption Ionisation Mass Spectrometry Imaging can separate the same donor's fingermarks deposited at different times based on intra-donor fingermark composition variability. Additionally, the hypothesis that the different times of deposition could be also determined was investigated in the view of linking the suspect at the scene at different times; the dating window of MALDI MSI within the selected molecular range was explored. Results show that it is possible to separate overlapping fingermarks from the same donor in most cases, even from natural marks. Fresh marks (0 days) could be separated from those of fourteen days of age, though the latter could not be distinguished from the set aged for seven days. Due to the use of only one donor, these are to be considered preliminary data, though findings are interesting enough to warrant further investigation of the capabilities and limitations of this approach using a larger cohort of donors.

Development of Improved DNA Collection and Extraction Methods for Handled Documents.

Handwritten documents may contain probative DNA, but most crime laboratories do not process this evidence. DNA recovery should not impair other evidence processing such as latent prints or indented writing. In this study, single fingermarks on paper were sampled with flocked swabs, cutting, and dry vacuuming. In addition, two extraction methods were compared for the sample type. DNA yields were low across all methods; however, this work confirms the ability to recover DNA from paper and the usefulness of the vacuum sampling method combined with the Chelex-Tween method. Stability of touch DNA deposits were compared over an 11-month period to better understand degradation that may occur over time. No significant difference in DNA recovery was observed, suggesting DNA deposits on paper are stable over an 11-month span.

An evaluation of two adhesive media for the recovery of DNA from latent fingermarks: A preliminary study.

Dual recovery of forensic evidence is beneficial for crime scene and evidence processing as it can potentially double the evidential value of a single source, even more so in instances of DNA fingermarks. The use of adhesive liftering media has shown comparable results to swabbing when dealing with trace DNA recovery. Gelatine lifters have displayed the potential to recover DNA from latent fingermarks with minimal alteration to friction ridge detail post application, yet their ability to recover DNA has not fully been explored. The aim of this research was to compare the use of gelatine lifters with more readily available masking tape in their ability to recover cellular material from latent fingermarks. Natural (n = 120) and sebaceous (n = 120) fingermarks were deposited and aged in time frames from fresh, 1-day, 2-day, 1-week, 2-weeks, and 1 month. DiamondTM Nucleic Acid Dye was used as a visualisation method for any DNA containing cellular material. Images of the fingermarks pre and post lifting, and on the lifting media were imaged using the DSC®5 system. The media's ability to recover cellular material was assessed using fluorescent particle analysis by the employment of the free software ImageJ. Fluorescent particles could be observed on the lifting media post lifting with the use of DiamondTM Dye. Time was not seen to influence the variation in the number of fluorescent particles observed. The use of gelatine lifters was found to have a higher amount of recovered DNA containing cellular material than masking tape. Visualisation of particles on masking tape were inhibited by its porosity and absorption of the dye. Some fingermark detail could be observed in the gelatine lifters. The DSC®5 system was suitable for imaging fingermarks stained with DiamondTM Dye.

Independent component analysis of hyperspectral data measured from overlapping latent fingermarks: Forensic potential of independent component images.

Overlapping fingermark images are sometimes discarded because fingermark collation for the individual fingermarks is difficult. Fluorescence hyperspectral data (HSD) measured using the models of double overlapping fingermarks obtained under the excitation of a high-power, continuous wave, green laser is suitable for obtaining individual fingermark images. However, there are limitations such as the problems on each spectrum of the individual fingermark and the forensic value of the obtained images. In this study, independent component analysis (ICA) was applied to the fluorescence HSD obtained from the models of doubly overlapping fingermarks, to obtain independent component (IC) spectra and the corresponding IC images. Forensic value of the obtained IC images was examined, considering the possibility of fingermark collation in masked fashion to the model sample information. The IC images obtained from the HSD had enough potential to enable extracting twelve minutiae required for fingermark collation if the image quality was good.

The use of liquid latex as a pre-treatment to recover debris-covered latent fingerprints from exterior surfaces of vehicles.

This study evaluated the effectiveness of using liquid latex as a pre-treatment for fingerprint recovery from the exterior surfaces of vehicles in summer. The sample of this study was 540 sebaceous latent fingerprints deposited on the lower body of three vehicles. Thirty control and thirty experimental fingerprints were deposited on each vehicle, and the experiment was repeated three times. The three vehicles were driven daily for either 2, 3, or 4 weeks after the deposition of fingerprints. After the vehicles reached their designated debris accumulation duration, the latent fingerprints in the control groups were developed with black fingerprint powder. Liquid latex was applied onto the fingerprints in the experimental groups, and they were subsequently developed with black fingerprint powder. A chi-sure test indicated that there was a significant difference in fingerprints recovery performance between two methods (X2  = 4.903, d.f. = 1, p = 0.027). An odds ratio test indicated the control method increases the probability of fingerprint recovery by 1.54 times. A Fisher's exact test was used to evaluate the quality of fingerprints recovered from both methods and it indicated that there is no significant difference in quality using the two methods (p = 0.058). This study indicated that the traditional fingerprint powder method performed better for fingerprint recovery from exterior surfaces of vehicles in summer.

Preliminary evaluation of Solstice® PF as a replacement carrier solvent for Australian fingermark detection.

HFE-7100 is a routine carrier solvent in amino acid-sensitive fingermark detection reagents such as ninhydrin and 1,2-indanedione/zinc chloride (IND/Zn). However, a potential EU ban on hydrofluoroethers may require reformulation of these treatments worldwide. Solstice® PF has shown promise as a replacement for HFE-7100 in the United Kingdom. However, the performance (and hence optimal formulation) of IND/Zn is impacted by differences in climate and substrate composition, necessitating assessments under local conditions for different regions. We present a series of preliminary investigations in an Australian context, using the IND/Zn formulation used by Australian forensic service providers. The general performance of Solstice® PF-based IND/Zn was comparable to that using HFE-7100 on three substrate types, three ageing periods (1, 7 and 30 days) and 5 donors. However, slight differences in colour and luminescence intensity, as well as increased ink diffusion, suggest chemical interactions with other reagent components that may affect stability. Specifically, Solstice® PF-based reagent formed a precipitate within a month of storage, though this did not affect performance over a 4 month period. HFE-7100-based IND/Zn was found to be marginally more effective than Solstice® PF when applied to incidental fingermarks. These results indicate that Solstice® PF is a satisfactory alternative carrier solvent to HFE-7100 in an Australian context, though users should be aware of possible limitations regarding compatibility with other evidence components (particularly inks) and shelf-life.

Studies into exfoliation and coating of Egyptian blue in methanol for application to the detection of latent fingermarks.

We have recently demonstrated that coated exfoliated Egyptian blue powder is effective for detecting latent fingermarks on a range of highly-patterned non-porous and semi-porous surfaces. In this extension of that work, we present our studies into an alternative approach to prepare exfoliated Egyptian blue coated with cetrimonium bromide and Tween® 20 using a simpler technique. The quality of the latent fingermarks developed with these exfoliated powders and the commercial powder were compared in acomprehensive study. Depletion series of natural fingermarks from a wide range of donors (12 males and females) deposited on non-porous (glass slides) and semi-porous (Australian banknotes) surfaces were used in this study. Enhancement in the performance of the coated exfoliated particles compared to the commercial powder was observed, particularly in the case of aged fingermarks and polymer banknotes as challenging substrates.

Greasy fingermark detection on porous surfaces using Oil red O in a gas phase: Comparison with Oil red O in solution.

Oil Red O is a fingermark reagent that is useful for developing greasy fingermarks. Classic Oil Red O formulation is based on methanol-water solution. The use of solvent can be harmful to the forensic practitioner and the environment. Moreover, solvent can destroy hand writing and biological traces. In this paper a new solvent-free Oil red O deposition method have been proposed. Experimental method is based on Oil Red O deposition from a gas phase in reduced pressure conditions. 1728 split, greasy fingermarks deposited on paper have been developed with the new method and a benchmark one. The development results have been compared. The general performance of the new method has been found inferior to the solvent based formulation. However, in most cases both methods were comparable. This shows that the experimental method could be a possible alternative to the classic one in the cases where drawbacks connected to the solvent use are unacceptable. Even though, presented results are promising, more research and optimization is necessary, before the new method can be included into the forensic expert toolbox.

Effects of chemical warfare agent decontaminants on trace survival: Impact on fingermarks deposited on glass.

Following a chemical incident involving chemical warfare agents or more broadly, chemical weapons, there are two possible approaches in dealing with the traditional forensic analysis of contaminated exhibits. The first is to analyze the contaminated items under safe conditions (i.e. in laboratories dedicated to the handling of such substances), while the second relies on item decontamination prior to processing them in traditional forensic laboratories. One of the main limitations of the latter is the possible degradation or destruction of traces caused by the decontamination process. Hence, it is crucial to have as much information as possible on the impact of different decontamination agents and procedures on traces. This research presents experimental results on the recovery of fingermarks on glass after the application of decontaminants typically used in case of chemical incidents. The impact of 11 decontaminants on fingermarks deposited on glass and on the subsequent enhancement with cyanoacrylate and Small Particle Reagent (SPR) was evaluated (by visual examination) by four evaluators. The results of the study demonstrated that the persistence of fingermarks on glass is highly dependent on the type of decontaminant used. Decontamination agents based on the principle of nucleophilic substitution to neutralize toxic chemicals allowed good subsequent development of fingermarks with SPR. Powdered decontaminants did not show any indication of alteration of fingermarks, whereas decontamination with oxidants leads to variable results.

Fingermark visualisation on compostable polymers - A comparison among different procedures as an outcome of the 2020 collaborative exercise of the ENFSI Fingerprint Working Group.

In 2020 the Fingerprint Working Group (EFP-WG) of the European Network of Forensic Science Institutes (ENFSI) undertook a collaborative exercise (CE) with the aim of assessing the ability in developing fingermarks on an item constituted of compostable polymers. The test was prepared and managed by the officially established advisory group. The characteristics of the CE are summarised. Different approaches emerged from the outcomes. Multi-Metal Deposition (MMD) was used as reference method for the assessment of the results. It demonstrated to be the more effective and consistent technique for fingermark visualisation on the specific kind of Mater-Bi® compostable polymer used for the test. Alternative techniques, such as Vacuum Metal Deposition (VMD), cyanoacrylate fuming, followed by Basic Yellow 40 dye staining or in its fluorescent forms demonstrated to be effective methods. However, it seems that the operational conditions need to be controlled in order to find the optimal ones. Conversely, data does not support the use of amino acid sensitive techniques.