Synthesis and On-Field Testing of Novel Low-Cost Latent Fingerprint Development Powders

Gurpreet Singh Suri^1* and Mohammad Al-Suwaidi^2
*Correspondence: Gurpreet Singh Suri, Forensic Division, Imperial College London, University of Central Lancashire, Preston, UK, Tel: 07466956549, Email:

Keywords

Latent fingerprint • Powder dusting • Carbon powder • Forensic science • Fingermarks • Magnetic powder

Introduction

Evidence identification and collection are one of the most critical processes in crime scene investigation. Various types of evidence are sought after at a crime scene, but the key evidence that is undeniably critical for any case are the fingerprints. This is because fingerprints represent a unique identification marker for each individual that can easily differentiate between people. However, the presence of fingerprints on various types of surfaces at a crime scene makes it a challenge to successfully identify and record it. It is the quality and details of these recorded or extracted fingerprints that is adjudged permissible in the court for criminal conviction [1].

A good and permissible fingerprint for judicial purposes must meet some official criteria that are based on a number of parameters. For instance, the most frequent judicial scrutiny of submitted fingerprints is based on errors in the ACE-V process. This includes, but not restricted to, 4 stages of forensic expert’s methodology in presenting the fingerprint evidence. These stages are grouped as analysis stage, comparison stage, evaluation stage and verification stage. Furthermore, the qualification and experience of the fingerprint expert handling this critical piece of evidence is also often taken into account during a ruling. Finally, the procedure and the elements involved at various stages of extracting and developing the fingerprints should be well-established and scientifically acceptable [2,3].

Latent fingerprint development has evolved a great deal over the century, especially with regards to various chemical and physical methods that are employed to uncover hidden fingerprint evidences from different surfaces. However, the pros and cons exist for each of the physical and chemical methods and therefore, it is the awareness and experience of the fingerprint expert to employ an appropriate method for successful development of latent fingerprints [4]. A rule of thumb is to use an appropriate fingerprint powder with specific surface-related properties to develop the latent fingerprints from any solid surface. However, often the commercial fingerprint powders are limited to only specific surfaces and development conditions which restrict its use on other surfaces, crime scenes or even to the level of user expertise.

SIRCHIE^® is a current global leader among the manufacturers of latent fingerprint powders and other kits and tools used extensively for forensic examination. More than 120 countries and their law enforcement agencies use SIRCHIE^® products, including the highly advanced and reputed the General Department of Forensic Science and Criminology, Dubai Police. The authors’ research group was approached by this prestigious department of Dubai Police to explore and exploit the group’s nano-technological advancement towards fingerprint applications. Therefore, the focus of this research was to improve the quality of developed latent fingerprints, by synthesizing highly efficient novel nanoparticles-based fingerprint powders that are low-cost and can be used on both porous and non-porous surfaces. Furthermore, the developed fingerprinting powders were run through an automated database (AFIS) by the Dubai Police Department, to minutely analyse the level of details exhibited by the novel powders, in comparison to the SIRCHIE^® products.

Materials and Methods

The reagents used for the experiments were purchased from Sigma Aldrich and Sirchie Co. Ltd. The chemicals were used as it is without any modifications and all the safety procedures were followed. Fumehood was used constantly for all the fuming and strongly odoured liquids. n-Dodecyl trimethoxysilane, Tetraethyl-orthosilicate 99.9% (TEOS), concentrated Ammonium Hydroxide (28%), Mesitylene 98% and Activated Charcoal powder were purchased from Sigma Aldrich. Iron (II) chloride tetrahydrate, 99+% and Iron (III) chloride hexahydrate, 99+% were purchased from ACROS organics of FisherScientific. Regular Hi-Fi Volcano Latent Print Powder (CAT.No. 101L), Magnetic Latent Print Powder (No. BPM114L), Standard Size Fiberglass Brush with Plastic Handle, White 11/2 inch x 2 inch Hinge Lifter and Standard Magnetic Powder Applicator Anodized Aluminium were purchased from SIRCHIE^®.

The fingerprint development powders were characterised using primary analytical techniques such as SEM (Scanning Electron Microscopy), XRD (X-Ray Diffraction method) and particle sizer. In this work, Bruker D2 Phaser diffractometer was used with a DIFFRAC SUITE software, scan time of 5 minutes, Cu wavelength of 1.5406 Å and a scan range of 2θ = 5 to 80°. Malvern Mastersizer 2000 was used for analyzing the particle size using a vortexed suspension in deionised water. FEI Quanta 200 SEM was used to study the morphological appearance of the synthesised materials. An accelerating voltage of 20 kV was applied for SEM analysis and the spot size between 2 to 3 was used to get high quality images. The novel powders were subjected to a series of physical tests in laboratory environment followed by on-field testing and AFIS match scoring at Dubai Police Department.

Synthesis of silica nanoparticles based powder

Silica nanoparticles can be easily synthesised using modified Stober’s method [5]. In a reaction flask of 500 mL, 125 mL of absolute ethanol was mixed with 125 mL ammonium hydroxide (5M). The solution was kept for ultra-sonication treatment in a water bath for 5 minutes. At the end of this, 17.5 mL of tetraethyl orthosilicate (TEOS) was added in the reaction flask and the solution was treated again in ultra-sonication bath for another 30 minutes. A white suspension was achieved at the end of sonication period that was subjected for dialysis with deionised water for 2 to 4 days until the pH of the dialysis reached pH 7. The suspension was centrifuged or vacuum filtered, dried 50°C oven and finely ground to obtain a white fingerprint powder. The powder hereon will be referenced to as basic silica, for the rest of the text.

Magnetised silica powder

In a reaction flask of 500 mL, 0.85 grams of iron (ll) chloride and 2.16 grams iron (lll) chloride was measured and were mixed in solution containing (20 mL ethanol and 40 mL deionised water) while it was covered with Para film. The reaction mixture was then mixed with 250 mL of basic silica suspension or 1g of silica powder and kept for stirring for 1 hour. 30 mL ammonium hydroxide (5M) was prepared and was added to the solution drop wise while it was stirring. The final mixture was kept for stirring for another hour, sample was filtered using vacuum filtration technique and deionised water was added to wash out the excess of ammonium hydroxide. Finally, the sample was kept to dry at 50°C oven overnight and ground to a fine powder. The powder hereon will be referenced to as magnetised silica for the rest of the text.

Mesitylene-charcoal based powder

Activated charcoal was commercially purchased from sigma-aldrich with an approximate size of about 75 microns. 60 mL of mesitylene was taken in a conical flask and 4 g of activated charcoal was added to it with constant stirring. After 20 mins, the solution was kept in a hydrothermal bomb for 36 hours at 200°C. The solution was then filtered and washed with copious amounts of deionised water, followed by drying the filtered product at 80°C for 2 hours using a hot air oven. The sample obtained as fine black powder with characteristic mesitylene smell. The powder hereon will be referenced to as basic mesitylene for the rest of the text.

Magnetised mesitylene-charcoal powder

60 mL of mesitylene was taken in a conical flask and mixed with 3g of activated charcoal with continuous stirring for 10 mins. The solution was sonicated for 60 mins using sonicator water bath, where 60ml of mixed iron solution (prepared separately as described earlier) was added dropwise after 10 mins into sonication. The mixture was left for the rest of the sonication duration, after which 120 ml of 5M ammonia solution (in 1:3 water-ethanol solution) was added dropwise and sonicated for another 30 mins. The final solution was then filtered, washed and dried at 80°C for 2 hours. The sample obtained as fine black magnetic powder with characteristic mesitylene smell. The powder hereon will be referenced to as magnetised mesitylene for the rest of the text.

Characterisation techniques

The fingerprint development powders were characterised using primary analytical techniques such as SEM, XRD and particle sizer. In this work, Bruker D2 Phaser diffractometer was used with a DIFFRAC SUITE software, scan time of 5 minutes, Cu wavelength of 1.5406 Å and a scan range of 2θ = 5°C to 80°C. Malvern Mastersizer 2000 was used for analyzing the particle size using a vortexed suspension in deionised water. FEI Quanta 200 SEM was used to study the morphological appearance of the synthesised materials. An accelerating voltage of 20 kV was applied for SEM analysis and the spot size between 2 to 3 was used to get high quality images.

Powder testing details

All the fingerprints were deposited by authors working in lab and the senior fingerprint expert of Dubai police using the thumb impression. The procedure which was followed for depositing the thumb prints involved slight rubbing of the thumb to the forehead to collect sweat and oily secretions of the body, followed by depositing the prints on the surfaces using varying degree of forces. The thumb was not pre-rinsed with any soap or solvents, so as to accumulate mixed natural body secretions, similar to that found in the fingerprints at the crime scenes. This ensures that any cosmetics and other contaminants can contribute to test the efficiency of the powders in developing latent fingerprints. Two sets of fingerprints were deposited in each experiment on a particular surface so as to compare the novel powders with the SIRCHIE^® products. The developed fingerprints were photographed in lab using iPhone 6, 8MP, f/2.2 camera with phase detection autofocus and dual LED flash, whereas it was tape-lifted and tested for AFIS at the Dubai Police Department.

Five surfaces were used for testing the fingerprint powders based on their classification of porous or non-porous nature. Non-porous surfaces included glass slides, polymer plastic bags and aluminium foil, whereas the porous surfaces included the cardboard and paper. The non-magnetised basic powders were used with a fibre glass brush and standard brushing techniques employed by fingerprint experts. Firstly, a good amount of the powder was dropped on to a platform, followed by dipping a brush in it gently for its strands to accumulate a good amount of powder. The brush is then shaken slowly over the entire surface to be analysed and further dipped in the powder available on the platform, in case more powder is required to be sprinkled. Finally, the brush is stroked gently over the surface in one direction only at first to observe if any fingerprints develop. To test the powder’s efficiency of adhering to the fingerprints, more rigorous approach is taken which involved using more forceful brush strokes and in all directions. This ensures the optimum affinity or efficiency of the powder to adhere to the latent fingerprints without getting damaged due to brushing. However, extremely rough brushing techniques can cause abrasion of fingerprints, irrespective of the efficiency of the fingerprint development powder. Therefore, certain practice and skill is required to safely develop latent fingerprints using powders, without permanently damaging any details during brushing.

A magnetic applicator is used for testing the magnetic fingerprint powders that overcomes most of the brushing limitations. The magnetic brushing involves cleaning the tip of the magnetic applicator brush with a clean alcohol tissue, followed by magnetically attracting the powder to it and carefully dropping the powder at the exact site in focus. Next, the powder is again lifted using the magnetic brush and normal brushing technique is used gently all over the fingerprint surface. Finally, dropped powder is magnetically lifted again using the magnetic brush and standard brushing technique is used. Care should be taken as to not press the magnetic brush on the surface as it could diminish or eradicate the prints permanently. However, such a practice is again not advisable for actual crime scene investigation, along with any rough brushing techniques, as it may cause permanent loss of fingerprint evidences.

The analysis of developed fingerprints involved close inspection of ridge pattern by visual observations using a magnifying glass. This practice is purely based on the experience and knowledge of the fingerprint expert, who decides to take forward the presumably good quality powder samples for next stages of analysis and testing. This procedure was repeated on a virtual crime scene, where trainee fingerprint experts at the department of Dubai Police were asked to locate and develop the latent fingerprints. This ensured understanding of the performance of the synthesised powders in regard to the skills and expertise levels of a professional’s on-field.

Furthermore, all the developed fingerprints were lifted using a SIRCHIE^® tapelifter, which is a standard procedure to collect fingerprint evidences, in addition to photographic recordings. It is done by using a contrasting tape background in regard to the colour of the developed fingerprint, which is placed on one end of its sticky surface at a good margin from fingerprint boundaries. Next, the tape is slowly pressed onto the surface and slight even pressure is applied by rubbing the surface, so as to uniformly stick the adhesive to the developed fingerprint pattern, avoiding any air bubbles in it. The tape is then lifted slowly and carefully from the surface without touching the area and side containing the fingerprint pattern.

This tape lifting method ensures that the novel powders were able to keep the developed fingerprints pattern intact and facilitate its transfer to another substrate without compromising its quality or levels of detail. It also ensures the storage stability of the lifted patterns in optimum conditions for prolonged periods of time without deterioration of the print.

AFIS analysis

The photographed or lifted latent fingerprints were analysed using either of the mode functions of the AFIS that uses both pictures and physical surfaces for analysis. There are a number of parameters that are adjusted and corrections are applied before hitting for search in the AFIS database. These adjustments include the geometric image accuracy, signal to noise ratio, modulation transfer function, gray-scale range, linearity and uniformity [6,7]. One of the most important features of AFIS analysis is the likelihood ratios that facilitates the mark to print comparison to give a score. There could be an inherent variability of AFIS scoring for between-fingers analysis, but overall a number of factors play an important role in obtaining an accurate match. These are directly linked to the quality of the developed fingerprint that evidently enhances the total number of scoring minutiae patterns [8,9].

SAFRAN MorphoBIS 2.0 from MorphoTrak^® software was used by Dubai Police headquarters to analyse all latent fingerprints and match it effectively to its criminal database. This software has an option to automatically or manually detect fingerprint traits such as ridges, whorls and loops. There is a score which is assigned to the fingerprint evidence based on AFIS’s detection of these traits and a unique code is run for a potential match in the criminal database. The use of AFIS is entirely based on the skills and knowledge of the fingerprint experts as damaged or partially developed fingerprints can also yield positive matches based on the region that is focussed on for analysis.

Conclusion

The 3 powders that were synthesised towards latent fingerprint development application, proved to be highly efficient and cost-effective. The silica based powders have the potential to yield white fingerprints on all nonporous surfaces such as glass, aluminium foil and plastic bags. However, to overcome its weaknesses of colour contrast and application to porous surfaces such as wood, paper and cardboard, novel mesitylene-based powders were synthesised. The undiscovered affinity of mesitylene towards both sweat and oily residues of the fingerprints make these powders show remarkable properties on both porous and non-porous surfaces. Furthermore, on-field testing of these powders by fingerprinting experts of Dubai Police Department highlights its key advantages for re-developing fingerprint evidences that have already gone through a chemical development procedure. Therefore, these novel powders have high commercial value due to its cheaper cost of synthesis, high performance and added advantages.

However, in order to make these products commercially viable, a focus is required to tackle the key problems of wettability and low magnetism that comes along the strengths of mesitylene. There is a possibility that the chemical hindrances or binding site restrictions limit the incorporation of magnetic nanoparticles and mesitylene together onto the activated charcoal framework. Another reason that contributes towards the weaknesses of the wettability and lower magnetism is that the extremely small iron nanoparticles are masked by the bulkier mesitylene groups or its interaction with the carbon framework is hindered. In fact, the wettability of the magnetised-mesitylene powder is certainly due to excessive unwashed mesitylene remaining onto the product that gets easily detached from the host material onto the substrate. Therefore, further work would be needed to stabilise the complex by using specific binding site interaction or surface functionalisation approach so that both the organic and inorganic elements could be constituted together. Nonetheless, the experts’ report detailed by the Dubai police department concluded equal performance and strengths of the synthesised mesitylene based powders, as that of the commercial powders. This promotes further research in this direction for exploring the commercial viability of these novel powders.

Declarations

Ethics approval and consent to participate

All fingerprint used in this work are provided by the authors and members of their team, both in lab and in the Dubai Police’s fingerprint testing team. The fingerprints were taken with consent and completely randomised prior to testing, in order to prevent any biased results. No fingerprints were taken any unauthorised person, or without permission from anyone, along with all ethical approvals granted by both university research team and Dubai Police’s forensic department. There are no conflicts of interest in this study and no funding grants applicable to be disclosed.

Consent for publication

Both authors consent to publication. All donors of fingerprint marks consent to publication

Availability of data and materials

Data can be shared on request, in regard to some aspects of measureable research entities. It is available in the form of report and analysis files from software, wherever applicable.

Competing Interests

The authors declare that they have no competing interests.

Funding

The commercial powders, brushes and few raw materials were funded personally using authors’ own contributions. Some raw material and chemicals were donated by second author’s Master degree research on good will by his supervisor Dr Sen, who is acknowledged here. No other funding was applicable or provided.

Authors Contributions

Dr. Gurpreet Singh is the main author as he has done most of the advanced synthesis and characterisation work in the lab. The second author Mr Mohammad Alsuwaidi has carried out substantial work on initial synthesis, physical development of latent fingerprints, as well as final analysis using commercial AFIS software.

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