Vaughn G. Sears

A methodology for finger mark research

Currently there is no standard way of carrying out research into finger mark enhancement techniques. Individuals, groups or establishments tend to use different methodologies depending on a number of factors, especially finance and time. However, data published in the literature can be misleading to the forensic community if the data generated reflects research involving very few finger marks or if those finger marks have been deliberately doped with an unnatural balance of sweat or an unusual contaminant. This paper presents an experimental methodology which is intended to establish minimum standards for those carrying out finger mark enhancement research (at least within the United Kingdom) and bring some consistency to the process. It will aim to identify the many variables encountered when dealing with finger marks and suggest experimental methods to take these into account. It will also present the key stages of the progression of a process from a laboratory concept to a tool used on operational work.

Development of a GC‐MS Method for the Simultaneous Analysis of Latent Fingerprint Components

ABSTRACT: Latent fingerprint residue is a complex mixture of organic and inorganic compounds. A full understanding of the composition of this mixture and how it changes after deposition is lacking. Three solvent systems were compared for the simultaneous extraction and derivatization with ethyl chloroformate of selected amino and fatty acids from a nonporous substrate (Mylar®) for subsequent analysis by gas chromatography‐mass spectrometry. A solvent system comprised of sodium hydroxide, ethanol, and pyridine was found to be the most effective. This method was applied to the analysis of latent fingerprint residue deposited on Mylar® and preliminary data are presented. Twelve amino acids (e.g., serine, glycine, and aspartic acid) and 10 fatty acids (e.g., tetradecanoic, hexadecanoic, and octadecanoic acids) were identified. The potential application of this method to further the understanding of latent fingerprint chemistry has been demonstrated.

Nano-scale composition of commercial white powders for development of latent fingerprints on adhesives.

Titanium dioxide based powders are regularly used in the development of latent fingerprints on dark surfaces. For analysis of prints on adhesive tapes, the titanium dioxide can be suspended in a surfactant and used in the form of a powder suspension. Commercially available products, whilst having nominally similar composition, show varying levels of effectiveness of print development, with some powders adhering to the background as well as the print. X-ray fluorescence (XRF), analytical transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and laser particle sizing of the fingerprint powders show TiO(2) particles with a surrounding coating, tens of nanometres thick, consisting of Al and Si rich material, with traces of sodium and sulphur. Such aluminosilicates are commonly used as anti-caking agents and to aid adhesion or functionality of some fingerprint powders; however, the morphology, thickness, coverage and composition of the aluminosilicates are the primary differences between the white powder formulations and could be related to variation in the efficacy of print development.

Reagents for the chemical development of latent fingerprints: scope and limitations of benzo[f]ninhydrin in comparison to ninhydrin.

Benzo[f]ninhydrin was compared to ninhydrin for fingerprint development on paper. Overall, the performance of ninhydrin on exhibits was slightly better than that of benzo[f]ninhydrin. The significant advantages of the benzo[f]ninhydrin over ninhydrin were the much stronger fluorescence it gave after treatment with zinc salts and a slightly quicker reaction under ambient conditions. This fluorescence is, however, similar to that obtained with other reagents, such as DFO or ninhydrin analogs. These advantages apparently are not sufficient to justify regular usage of benzo[f]ninhydrin, especially when one considers its low solubility and high cost.

A comparison of multi-metal deposition processes utilising gold nanoparticles and an evaluation of their application to ‘low yield’ surfaces for finger mark development

This paper reports a comparison of the effectiveness and practicality of using different multi-metal deposition processes for finger mark development. The work investigates whether modifications can be made to improve the performance of the existing process published by Schnetz. Secondly, we compare the ability of different multi-metal deposition processes to develop finger marks on a range of surfaces with that of other currently used development processes. All published multi-metal deposition processes utilise an initial stage of colloidal gold deposition followed by enhancement of the marks with using a physical developer. All possible combinations of colloidal gold and physical developer stages were tested. The method proposed by Schnetz was shown to be the most effective process, however a modification which reduced the pH of the enhancement solution was revealed to provide the best combination of effectiveness and practicality. In trials comparing the modified formulation with vacuum metal deposition, superglue and powder suspensions on surfaces which typically give low finger mark yields (cling film, plasticised vinyl, leather and masking tape), the modified method produced significantly better results over existing processes for cling film and plasticised vinyl. The modified formulation was found to be ineffective on both masking tape and leather. It is recommended that further tests be carried out on the modified multi-metal deposition formulation to establish whether it could be introduced for operational work on cling film material in particular.

Nanoscale Analysis of the Interaction Between Cyanoacrylate and Vacuum Metal Deposition in the Development of Latent Fingermarks on Low-Density Polyethylene*

Abstract:  Vacuum metal deposition (VMD) has been previously demonstrated as an effective development technique for latent fingermarks and in some cases has been shown to enhance prints developed with cyanoacrylate (CA) (superglue) fuming. This work utilizes scanning electron microscopy (SEM) to investigate the interactions of the two development techniques when applied to latent fingermarks on low‐density polyethylene. CA is shown to act principally on the eccrine deposits around sweat pores, where polymerization results in long polymer fibrils a few 100 nm in width. Subsequent VMD processing results in additional areas of development, for example, between pores. However, the primary mode of deposition of zinc is by interaction with the polymerized CA, the fibrils of which become decorated with zinc nanoparticles. Areas with limited CA deposition and no significant polymerization are also enhanced with the VMD process, resulting in increased print development.

A proteomic approach for the rapid, multi-informative and reliable identification of blood

Blood evidence is frequently encountered at the scene of violent crimes and can provide valuable intelligence in the forensic investigation of serious offences. Because many of the current enhancement methods used by crime scene investigators are presumptive, the visualisation of blood is not always reliable nor does it bear additional information. In the work presented here, two methods employing a shotgun bottom up proteomic approach for the detection of blood are reported; the developed protocols employ both an in solution digestion method and a recently proposed procedure involving immobilization of trypsin on hydrophobin Vmh2 coated MALDI sample plate. The methods are complementary as whilst one yields more identifiable proteins (as biomolecular signatures), the other is extremely rapid (5 minutes). Additionally, data demonstrate the opportunity to discriminate blood provenance even when two different blood sources are present in a mixture. This approach is also suitable for old bloodstains which had been previously chemically enhanced, as experiments conducted on a 9-year-old bloodstain deposited on a ceramic tile demonstrate.

Proteomics goes forensic: Detection and mapping of blood signatures in fingermarks.

A bottom up in situ proteomic method has been developed enabling the mapping of multiple blood signatures on the intact ridges of blood fingermarks by Matrix Assisted Laser Desorption Mass Spectrometry Imaging (MALDI‐MSI). This method, at a proof of concept stage, builds upon recently published work demonstrating the opportunity to profile and identify multiple blood signatures in bloodstains via a bottom up proteomic approach. The present protocol addresses the limitation of the previously developed profiling method with respect to destructivity; destructivity should be avoided for evidence such as blood fingermarks, where the ridge detail must be preserved in order to provide the associative link between the biometric information and the events of bloodshed. Using a blood mark reference model, trypsin concentration and spraying conditions have been optimised within the technical constraints of the depositor eventually employed; the application of MALDI‐MSI and Ion Mobility MS have enabled the detection, confirmation and visualisation of blood signatures directly onto the ridge pattern. These results are to be considered a first insight into a method eventually informing investigations (and judicial debates) of violent crimes in which the reliable and non‐destructive detection and mapping of blood in fingermarks is paramount to reconstruct the events of bloodshed.

Evaluation of the solvent black 3 fingermark enhancement reagent: Part 2 — Investigation of the optimum formulation and application parameters

A comparison is reported of the relative effectiveness to two formulations of the solvent black 3 (Sudan Black) reagent used to enhance grease contaminated fingermarks. These experiments compared the currently recommended ethanol-based formulation with a lower flammability system based on 1-methoxy-2-propanol (PGME) using natural, deliberately sebaceous and grease contaminated marks across a range of surfaces. It is shown that overall the PGME-based formulation was significantly better at producing good ridge detail on most surfaces for both natural and deliberately sebaceous prints, and for contaminated prints the ridge detail obtained with the PGME-based formulation was as good or better than that obtained with the ethanol formulation. Several smaller experiments were also carried out in order to provide additional information on the solvent black 3 process. These showed that solutions of age up to 2 years can still develop good ridge detail, but the colour of the stained mark may vary. It was also demonstrated that the currently recommended 2 minute treatment time often resulted in very heavy background staining and in practice significantly reduced treatment times can be recommended according to the nature of the surface present.

The Effects of Polymer Pigmentation on Fingermark Development Techniques

The effectiveness of latent fingerprint development techniques is heavily influenced by the physical and chemical properties of the deposition surface. The use of powder suspensions is increasing for development of prints on a range of surfaces. We demonstrate that carbon powder suspension development on polymers is detrimentally affected by the presence of common white pigment, titanium dioxide. Scanning electron microscopy demonstrates that patches of the compound are clearly associated with increased levels of powder adhesion. Substrates with nonlocalized titanium dioxide content also exhibit increased levels of carbon powder staining on a surface‐wide basis. Secondary ion mass spectrometry and complementary techniques demonstrate the importance of levels of the pigment within the top 30 nm. The association is independent of fingermark deposition and may be related to surface energy variation. The detrimental effect of the pigment is not observed with small‐particle reagent (MoS2 SPR) or cyanoacrylate (superglue) fuming techniques that exploit different development mechanisms.