Fingermark Visualisation Research Articles

UK National Fingerprint Collaborative Exercise 2022-23

In 2022–2023 the Defence Science and Technology Laboratory (Dstl) designed and conducted a two-part fingerprint Collaborative Exercise (CE). The CE focussed on fingermarks contaminated in blood as they provide a complex scenario for forensic units and it involved both fingermark visualisation and comparison elements. Participants were requested to treat the exercise as a major crime submission following internal protocols and were invited to provide comments relating to how the marks were deposited (if appropriate). Overall, forensic units performed well within both parts of the exercise. The exercise highlighted the importance of conducting sequential fingermark visualisation techniques, utilising additional lighting techniques and maintaining detailed notes throughout the fingerprint examination process. The outputs from the CE provided opportunities for forensic units to learn from one another, raise the level of understanding of blood contaminated fingermarks and identify areas of improvement which can be incorporated into internal processes.

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.

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.

Solvent-free strategies for developing latent fingermarks on paper: a review.

With growing environmental concern and supply chain uncertainty, now is a fitting time to re-evaluate solvent-free methodologies in forensic chemistry processes. Here, this paper reviews solvent-free approaches for fingermark visualisation, including chemical fuming and vapour phase treatments, dry-transfer treatments, application of heat, and thermal paper specific treatments. After providing historical context, three objectives have been emphasised: identify feasible scenarios for implementing solvent-free methods; showcase the effectiveness of solvent-free methods relative to their nearest solution-based equivalent; and estimate the technological readiness level of each method discussed. Having reviewed the literature, dry-transfer methods of developing latent fingermarks on paper were found to be the most promising and feasible solvent-free approaches for near-term implementation. Such methods make use of standard materials and equipment commonly found in forensic laboratories, are effective at fingermark visualisation, and mitigate most of the pressing issues pertaining to environmental concern and solvent scarcity.

Improving the technological readiness of time of Flight-Secondary Ion Mass Spectrometry for enhancing fingermark recovery - towards operational deployment

The processes routinely used by police forces to visualise fingermarks in casework may not provide sufficient ridge pattern quality to aid an investigation. Time of Flight-Secondary Ion Mass Spectrometry (ToF-SIMS) has been proposed as a technique to enhance fingermark recovery. The technique is currently designated a Category C process in the Fingermark Visualisation Manual (FVM) as it shows potential for effective fingermark visualisation but has not yet been fully evaluated. Here the sensitivity of ToF-SIMS on three common exhibit-type surfaces - paper, polyethylene and stainless-steel was compared to standard processes. An adapted Home Office grading scale was used to evaluate the efficacy of fingerprint development by ToF-SIMS and to provide a framework for comparison with standard processes. ToF-SIMS was shown to visualise more fingerprints than the respective standard process, for all surfaces tested. In addition, ToF-SIMS was applied after the standard processes and successfully enhanced the fingerprint detail, even when the standard process failed to visualise ridge detail. This demonstrates the benefit for incorporating it into current operational fingermark development workflows. Multivariate analysis (MVA), using simsMVA, was additionally explored as a method to simplify the data analysis and image generation process.

Degradation of polymer banknotes through handling, and effect on fingermark visualisation

The surface structure of mint (as-issued) and handled polymer five pounds sterling banknotes was studied by atomic force microscopy and laser scanning confocal microscopy. A total of 1856 fingermarks on mint and handled banknotes from four different issuing banks (Bank of England, Bank of Scotland, Royal Bank of Scotland and Clydesdale Bank) were visualised with Vacuum Metal Deposition (VMD), Cyanoacrylate Fuming (CAF) and, on Clydesdale Bank notes, magnetic fluorescent powder. VMD was significantly more effective in developing fingermarks on handled banknotes, across all the banks studied, although effectiveness varied with issuing bank. For example, on handled Bank of England notes 45% of marks showed ridge detail with VMD development and 28% with CAF; for Bank of Scotland handled notes success rates were 17% with VMD and 1% with CAF. Microscopy of degraded banknotes showed the loss of intaglio printing and the formation of a cracked surface structure in the handled notes. These features can lead to the trapping of powder, or contaminants, increasing quantity of development agent in fingermark background between the ridges, decreasing contrast and decreasing performance of powder-based fingermark development techniques. These same features can restrict the migration of components of the fingermark, preventing fingermarks degrading through spread of material and thus reducing potential formation of empty prints, so that VMD development is not adversely affected.

Preliminary investigations using Recover Latent Fingerprint Technology on unfired ammunition and fired cartridge cases

Previous studies have identified the potential benefit of the disulfur dinitride (S₂N₂) process to operationally relevant substrates. However, the majority of this work was conducted on prototype equipment that had substantial differences to the commercialised system (Recover Latent Fingerprint Technology (LFT)) in terms of design and chemical delivery. This paper evaluates the performance of Recover LFT on a problematic exhibit encountered within a fingerprint enhancement laboratory: unfired and fired ammunition. Three pseudo-operational experiments involving non-groomed, naturally handled fingermarks were conducted on the most commonly encountered types of ammunition used in crime in the United Kingdom (UK). In addition, Recover LFT was compared against Superglue Fuming followed by Basic Yellow 40 (BY40) Fluorescent Dye Staining (a commonly used alternative) to ascertain if the process provides added benefit to fingermark recovery rates. The results show that fingermark visualisation on small calibre cartridge cases remains difficult with few marks achieving enough ridge detail for comparison. However, this paper also shows that the novel Recover LFT process, which is still in its infancy and requiring optimisation, is no worse than currently implemented visualisation processes and is therefore worth further investigation.

An investigation into the detection of latent fingermarks on eco-friendly soft plastics packaging

Eco-friendly materials can present a challenge to fingermark recovery due to the variety of physical and chemical properties. Currently, there are no recommended guidelines for the recovery of latent fingermarks from eco-friendly soft plastics packaging. This work presents Phase 2 research trials for the detection of latent fingermarks on 13 different types of eco-friendly soft plastics packaging. In addition, these Phase 2 trials investigated other variables such as different fingermark donors, depletion series, ageing periods and a number of enhancement techniques that were assessed individually and in sequence with each other.The detection of latent fingermarks varied across the different substrates tested in this study and there was no specific sequence that favoured all of them. Nonetheless, sequence A (cyanoacrylate fuming - fluorescent dye staining – vacuum metal deposition) provided the highest amount of identifiable fingermarks overall. This is also the recommended sequence in the Fingermark Visualisation Manual for soft plastic packaging such as high- and low-density polyethylene plastic bags. The use of powder suspensions was the least successful across all substrates. The use of water and solvents present in certain enhancement techniques resulted in a negative effect on the structure and texture of some substrates used in this study. Statistical analysis of mark gradings from developed marks highlighted significant differences across substrates, ageing periods, donors and enhancement sequences. This work demonstrates that the current sequence in the FVM for soft plastics packaging is a good starting point for the detection of latent fingermarks on eco-friendly soft plastics packaging.

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.

The effect of corrosive substances on fingermark recovery: A pilot study

Corrosive substance attacks have become a growing issue within the UK. Although most commonly occurring in gang-related offences, there are high profile instances where this type of attack has been used to attack women to disfigure and destroy livelihoods. Despite the increase in such attacks, there has been very little published research into the recovery of forensic evidence from items used in these crimes. The effect of corrosive substances on the recovery of different types of forensic evidence is unknown, and there is no guidance for laboratories processing exhibits contaminated with corrosive substances regarding optimum treatments. This pilot study focused on establishing the effectiveness of a range of fingermark visualisation processes in recovering fingermarks on surfaces exposed to concentrated sulfuric acid (acid) and potassium hydroxide (alkali). Results indicate that on non-porous surfaces vacuum metal deposition and powder suspensions remain effective, and on porous surfaces fingermarks could still be visualised with physical developer. Alkalis were found to be more detrimental than acid environments in this limited study. The results demonstrate that fingermark recovery is still feasible on surfaces exposed to corrosive substances and provides encouragement that treatment protocols could be developed for this type of exhibit.

Replacing Synperonic® N in the Physical Developer fingermark visualisation process: Reformulation

The Physical Developer solution currently recommended for use in the United Kingdom for fingermark visualisation uses two surfactants: n-dodecylamine acetate (nDDAA) and Synperonic® N. Synperonic® N is covered by the EU directive 82/242/EEC, which sought to phase out chemicals with degradation products more harmful than their precursor. This study explores the replacement of Synperonic® N with alternative detergents and examines their ability to produce clear, stable solutions that are effective at developing fingermarks. The critical properties of the detergents were investigated, such as the critical micelle concentration and the hydrophilic-lipophilic balance, and planted mark comparisons were performed on promising formulations. Tween® 20 was deemed unsuitable due to the production of cloudy solutions and the requirement to age the formulation to improve effectiveness. Brij® C10 produced clear formulations; however, these were too stable causing unacceptably long exhibit processing times, and an additional preparation stage was necessary. Brij® L23, Brij® S10, Igepal® CO-630, Polyoxyethylene (10) tridecyl ether and Tergitol™ 15-S-9 also proved to be unsuccessful alternatives. Decaethylene glycol monododecyl ether (DGME) was found to be a suitable alternative to Synperonic® N and depletion series experiments suggested that a range of DGME and nDDAA detergent quantities were effective at developing marks. The processing time using DGME was similar to Synperonic® N and the most favourable ratio of reagents is proposed in this paper as a reformulated Physical Developer solution.

Fingermark visualisation on thermal paper – A comparison among different procedures as an outcome of the 2018 collaborative exercise of the ENFSI Fingerprint Working Group

In 2018 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 a thermal layer. 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 showing on average valid results. What is evident from data is that the preliminary inspection is highly advisable especially for the thermal side exploiting specific combinations of wavelengths and filters. In general, better performances were achieved by laboratories using multiple processing techniques. Conversely, few laboratories were capable to reach the expected results with only one step process. Finally, data does not support the use of cyanoacrylate, powders, and iodine on this specific substrate.

Determination of the most effective enhancement process for latent fingermarks on Clydesdale Bank and Royal Bank of Scotland £5 and £10 polymer banknotes

Fingermarks are commonly found at crime scenes and can be used to link an individual to an object and/or place. One common evidence type regularly encountered in the course of a criminal investigation is banknotes, and the recovery of fingermarks from these notes can give an indication of who has handled them. This study was carried out in order to determine the most effective sequential processing techniques for recovering latent fingermarks on the new £5 and £10 Clydesdale Bank and Royal Bank of Scotland polymer banknotes. No previous studies have been published on the recovery of latent fingermarks from these types of polymer notes; therefore, this work provides valuable insight into the challenges associated with these notes. Initial experimentation was done in order to determine the best light source to be used in combination with each sequential process tested. From this, infrared (730–800nm) and ultraviolet (350–380nm) light were chosen for use in the main study. Black iron oxide powder suspension and black magnetic powder were two of the enhancement treatments tested, both of which are recommended ‘Category A’ processes in the Fingermark Visualisation Manual produced by the Home Office. Superglue fuming – using PolyCyano UV—which is a Category C process was also used, as well as the recently developed infrared fluorescent powder, fpNATURAL®2. Three fingermark donors were selected for this study—one good, one medium and one poor—and each donor deposited a 10-mark depletion series onto both sides of each type of note. Superglue fuming (using PolyCyano UV) followed by black magnetic powder was found to be the most effective sequential process for enhancement of fingermarks on all note types tested. Infrared (730–800nm) light with an 815nm filter was the most effective light source for enhancing ridge detail for this enhancement sequence. This process is now being implemented for use with these note types in Scotland.

Positive control tests for fingermark development reagents

At the start of this study, no reliable, consistent, challenging and representative positive control test was commercially available for fingermark visualisation techniques.The goal of this study was to determine the lower limits of detection (LOD) of the fingermark visualisation techniques ninhydrin and 1,2-indanedione-ZnCl and developing positive control tests for these techniques.Spot tests with an amino acid solution were produced to determine the lower LOD’s. Secondly, a Dimatix Materials Printer (DMP) was used to print simulated fingermarks using different concentrations of an amino acid solution, to determine the lower LOD of ninhydrin and 1,2-indanedione-ZnCl using the DMP.Concept positive control tests were developed using the lower LOD of ninhydrin and 1,2-indanedione-ZnCl. These were later on adjusted, to form the definitive positive control tests, after a testing period of two months.

The effect of paint type on the development of latent fingermarks on walls

Despite recent advances in DNA technology, fingermark evidence remains a fundamental method of ascertaining an individual’s identity. Latent fingermarks are the commonest type of fingermark encountered at crime scenes. The Fingermark Visualisation Manual provides crime scene practitioner’s with sequential information regarding which enhancement processes are best suited for a range of deposition surfaces (Bandey et al., 2014) [1]. However, there are still many surfaces, such as painted walls where more knowledge is required regarding which development techniques provide optimum results. In this study, four paint types were tested (matt, silk, bathroom and eggshell). Fingermarks were deposited on painted simulated walls and aged for 1 day, 1 week and 1 month. Fingermarks were developed by three processes highlighted as the most frequently used by practitioners (magnetic granular powder, magneta flake powder and ninhydrin). The results showed that overall black magnetic granular powder outperformed both magneta flake powder and ninhydrin on all paint types. This contradicts current UK guidelines for enhancement of fingermarks on matt painted walls, as black magnetic granular powder is not a recommended process at present. SEM and SEM-EDX analysis showed distinct differences between matt paint and the three non-matt paints tested, which provides an explanation for the results obtained.

Evaluation of ninhydrin as a fingermark visualisation method – A comparison between different procedures as an outcome of the 2017 collaborative exercise of the ENFSI Fingerprint Working Group

In 2017 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 use of ninhydrin as a fingermark development technique in the laboratory. The test was prepared and managed by the officially established advisory group. The characteristics of the CE are summarised. The results indicate that ninhydrin is a robust methodology. Unexpected negative outcomes have been outlined and discussed, followed by an overview of the knowledge that has been gained.

The effect of DNA recovery on the subsequent quality of latent fingermarks: A pseudo-operational trial

The recovery of fingermarks and DNA from the same location at a crime scene can be problematic because of contamination issues associated with powdering or laboratory-based visualisation processes and/or the perceived destructive impact of commonly employed ‘swabbing’ approaches to DNA recovery. Previous research in a controlled environment demonstrated that it was possible to recover DNA and latent fingermarks from the same location on various substrates when an adhesive approach to DNA recovery was used. The aim of this research was to conduct a pseudo-operational trial into the dual recovery of DNA and fingermarks using gel lifters for DNA recovery. Participants were asked to voluntarily and anonymously donate a wide variety of porous and non-porous substrates post handling. No instruction as to fingermark deposition nor environmental storage was provided. BVDA gel lifters were applied to the substrates to replicate DNA recovery followed by the application of fingermark visualisation processes. The number and quality of the fingermarks was established using a grading approach. Application factors were also investigated to consider the effects of user variation. The results demonstrated that it was possible to recover DNA and fingermarks considered to be capable of supporting an identification. Fingermark quality post lifting was dependant on the substrates used. The weight applied to the gel during its application was a lesser contributing factor than the duration of its contact with the surface. There was a greater chance of leaving the fingermarks unaltered with the application of a low weight and instantaneous retraction.

A comparative evaluation of the disulfur dinitride process for the visualisation of fingermarks on metal surfaces

The disulfur dinitride process for fingermark visualisation was first reported a decade ago, with promising results obtained for a range of materials including metals. However, the friction sensitive nature of the material and difficulty of synthesis made routine use difficult. Many of these issues have since been addressed, making equipment and chemicals available to build an understanding of how the effectiveness of disulfur dinitride compares to other fingermark visualisation processes currently used on metal surfaces. This enables more informed advice to be given on selection of processes for treatment of metal items, an area of operational interest that encompasses weapons used in violent crime and the increasing incidence in metal theft. This paper reports a comparative study into the effectiveness of disulfur dinitride, cyanoacrylate fuming, vacuum metal deposition, gun blueing and wet powder suspensions on brass, bronze, copper and stainless steel. Experiments were conducted with the surfaces exposed to a range of environments including long term ageing, water/detergent washing, acetone washing and high temperature exposure. The results indicate that disulfur dinitride is an effective process for fingermark visualisation on metal surfaces, including those exposed to adverse environments, and may offer potential improvements over existing processes for those surfaces. Further work, including pseudo-operational trials, is recommended.

Visualising the past – An evaluation of processes and sequences for fingermark recovery from old documents

This study aimed to collect data on the effectiveness of most of the fingermark visualisation reagents currently used on porous surfaces on fingermarks aged for up to 90 years, significantly extending the timescales for which such information exists. A limited subset of the variables associated with processing of old fingermarks was explored, with a focus on the use of 1,8 diazafluoren-9-one (DFO), 1,2-indandione, ninhydrin, and physical developer. These techniques were used in sequence on batches of cheques between 11 and 32 years old, and on documents dating from the 1920s and 1940s. The potential for applying a physical developer enhancement process (blue toning) as the final step in the sequence was also explored. The benefits of using processing sequences on porous items were clearly demonstrated, with all processes in the sequence adding value in terms of additional marks found on the cheques up to 32 years old. In addition, physical developer was found to be capable of developing fingermarks up to 90 years old, whereas the amino acid reagents appear less effective on documents of 70 years and older. An experimental physical developer formulation with reduced environmental impact was found to be as effective as the existing process in these experiments. Blue toning was found to visualise an additional 10–25% of marks, and its wider use after silver-based deposition processes is recommended based on the evidence from this study.

Fingermark visualisation with iron oxide powder suspension: The variable effectiveness of iron (II/III) oxide powders, and Tween® 20 as an alternative to Triton™ X-100

The effectiveness of the current UK iron oxide powder suspension formulation, ‘C-IOPS-09’ (Triton X-100 based), for fingermark or latent fingerprint visualization is shown to be affected by variations between batches of the recommended iron oxide powder from Fisher Scientific (I/1100/53). When incorporated into the C-IOPS-09 formulation, a 2015 powder batch resulted in the detection of ∼19% fewer fingermarks, of broadly reduced contrast, when compared to powder suspension prepared with a 2008 batch of the same product. Furthermore, the 2015 powder batch was found to be unsuitable in experimental reduced-surfactant concentration powder suspension, because it caused surface-wide or background staining. The studies in this paper also investigated the use of Tween 20 surfactant as an alternative to the currently utilised Triton X-100, in preparation for the potential unavailability of Triton X-100 in the future. Powder suspensions prepared with Tween 20 surfactant solutions of 4% and 40% were shown to offer similar effectiveness to the currently recommended C-IOPS-09 formulation, when compared using the same batch of Fisher Scientific iron oxide powder (2008 or 2015). The difference between the 2008 and 2015 iron oxide batches was hence also evident with these alternative surfactant solutions. Particle size distribution analysis of the iron oxide powders in Tween 20 and Triton X-100 based surfactant solutions show that the more effective powder exhibits a higher sub-micrometre particle population than the less effective powder. This work leads to an improved specification for powder suspension formulations. This is demonstrated with an example powder suspension formulation which uses a 10% Tween 20 surfactant solution and iron oxide nanopowder (50–100nm) from Sigma Aldrich, which was shown to visualise 27% more fingermarks than the C-IOPS-09 formulation prepared with the 2015 Fisher Scientific powder batch, in a comparative study.