Development of latent fingermarks on thermal paper: Preliminary investigation into use of iodine fuming

Thermal paper finds its extensive use in the modern day life and could act as a vital piece of physical evidence carrying latent fingermarks. A large number of citations are available in literature suggesting various techniques to develop these marks but all are suffering with one or the other drawbacks such as complex and cumbersome procedure, pre- or post-treatment, background coloration and efficiency to develop aged fingermarks. In present study, a very simple and novel method involving iodine fuming has been suggested to develop fingermarks which were not only permanent but also without any background coloration. The suggested method does not involve any pre- or post-treatment of the substrate and was able to develop very old fingermarks (upto >1 year). In this study an attempt has been made to explain the reaction mechanism of the process. In case of different types of thermal papers, presence of different substituents on leuco dye (lactone ring) structure resulted in development of different colored fingermarks upon reaction with iodine. Sebaceous material laden marks have been found to be more intensely developed as compared to eccrine marks, and the difference was more pronounced in case of aged fingermarks.     

Development of latent fingermarks by aqueous electrolytes

In this work we present our observations on the interaction between metallic (copper, aluminum, iron, brass, zinc) and non-metallic (glass and plastic) surfaces bearing latent fingermarks and several aqueous electrolytic solutions. Good quality fingermarks could be observed on some of the metallic and even on non-metallic surfaces after such treatment. The influence of factors such as time interval from deposition, pH of the electrolytes, wiping the latent marks prior to processing and the presence of a second metal on the quality and permanence of the developed impressions have been studied. As a rule, sebaceous marks provided much better quality impressions on all the surfaces. Initial explanations based on electrochemical processes are suggested.     

A preliminary investigation into the use of alginates for the lifting and enhancement of fingermarks in blood

Recent studies have reported the use of alginate in the lifting and subsequent enhancement of footwear marks in blood. A study was set up to assess the use of such a method in the treatment of fingermarks in blood on a variety of porous, non-porous and semi-porous surfaces. Other variables included ageing of the fingermarks in blood and the application of chemicals prior to or post-alginate lifting. All different variations were compared to direct chemical treatment of the substrate. The results demonstrated that alginate is not compatible with certain substrates (e.g. glass and tile). On substrates that were compatible with alginate (e.g. fabric and paper), the enhanced fingermarks on the alginate cast and the enhanced fingermarks on the post-alginate substrates appeared, overall, inferior compared to direct chemical enhancement without the use of alginate. A further variation using water-based protein stains directly mixed with the alginate appeared to provide enhancement directly on the substrate as well as simultaneous lifting and enhancing the fingermarks in blood on the alginate cast.     

Printed artificial sweat as replacement for natural fingermarks: Qualitative and quantitative approach considering an amino acid reagent

The study presented in this paper aims at assessing how printed fingermarks can be used to generate realistic latent marks bearing varying quantities of materials to be detected. Considering dilution series of artificial sweat (eccrine secretion) and 1,2-indanedione/zinc as amino acid reagent, we assessed how printed marks behave in comparison to natural fingermarks provided by a set of 30 donors. The results were assessed in terms of relative intensity (contrast, luminescence) and expert grading (ridge details, overall quality). With regards to the set of 30 donors, this study brought a quantitative look to the influence of intra- and inter-variability on the relative intensity values observed when processing natural fingermarks. This provided new data to further understand the concept of “donorship”. With regards to the use of printed marks, it has been illustrated how dilution series of a concentrated solution allows covering a range of cases: unnatural marks (intensity values well above those obtained with donors), rich marks (corresponding to fingermarks left by good donors), and faint marks (associated with the kind of results observed with poor donors). Such a range of detection performance offers the possibility to generate fine-tuned detection exercises of varying difficulty levels. Printed items made of artificial sweat could hence constitute a valuable alternative to natural secretions in the context of education and proficiency testing.     

Recovery of DNA from Latent Fingerprint Tape Lifts Archived Against Matte Acetate

This study was driven by court order to examine methods to remove, extract, and STR‐type potential DNA entrapped between latent fingerprint lifting tape and matte acetate that was collected from a 1977 crime scene. Results indicate that recovery of appreciable quantities of DNA is more challenging once adhesive is attached to matte acetate cards and even more difficult when fixed following black powder enhancement. STR amplification of extracts from entrapped fingermarks collected following the dusting/lifting procedure did not produce robust profiles, and extraneous peaks not expressed by print donors were detected for some samples. A hearing was set to argue whether there was DNA remaining to be tested, and if so, whether that DNA could be exculpatory in this postconviction matter. The studies herein provided the basis for the court's decision to not require the testing.     

Methods for the enhancement of fingermarks in blood

Fingermarks formed in or by blood often require specific development techniques. This review examines techniques and materials that may be used to enhance and record fingermarks deposited in blood or fingermarks generated by blood-contaminated papillary ridges. A large number of techniques are presented here and are discussed from a chemical as well as practical perspective. It is concluded that an optimized sequence of techniques targeting both latent (non-bloody) and bloody fingermarks must be applied to detect and enhance the maximum number of marks, and therefore optimize the information content from exhibits that may bear marks in blood.     

Lifting techniques for finger marks on human skin previous enhancement by Swedish Black powder — A preliminary study

An examination was done to investigate whether certain lifting techniques can lift recovered latent fingerprints on human skin surfaces of living subjects. For recovery Swedish Soot powder mixture (Swedish Black) was used.Donors intentionally placed fingerprints on the skin surface of living subjects. Finger marks were then in all cases recovered with Swedish Black powder. The procedure was repeated after 1 h and 4 h. Treated finger marks were secured and preserved as latent fingerprint evidence by different lifting processes. Having examined skin surfaces and finger marks we observed that the lifters such as white instant lifter, white fingerprint gelatin, black fingerprint gelatin, silicone, transparent adhesive tape, are suitable. Moreover, white fingerprint gelatin and white instant lifter proved to be very good at lifting treated finger marks. Black fingerprint gelatin was very good also, but finger marks were examined by slant light.     

Reactions of latent prints exposed to blood

We explored whether an undeveloped latent print (fingermark) exposed to blood and later developed by enhancement with blood reagents such as amido black (AB) or leucocrystal violet (LCV) could appear as a genuine blood mark. We examined three different experimental conditions. In Experiment I, fingermark residue only was tested, as a control to confirm that fingermark residue alone does not react with the blood reagents AB and LCV. Experiment II investigated whether latent fingermarks exposed to blood dilutions could be treated with AB or LCV and subsequently appear as a genuine blood mark enhanced with AB or LCV. Experiment III tested whether latent fingermarks exposed to whole blood could be processed with AB or LCV and subsequently appear as a genuine blood mark enhanced with AB or LCV.The present study found that indeed, fingermark residue alone does not react with the blood reagents AB and LCV. In Experiment II, an interaction occurred between the fingermark residue and the diluted blood that caused the ridges to appear a red color. In the present study, this interaction is called a faux blood mark. While the faux blood mark phenomenon occurred most often following exposure to diluted blood, it did not occur consistently, and a predictable pattern could not be established. However, the reaction occurred more frequently following extended fingermark residue drying times. Faux blood marks are distinguishable from genuine blood marks prior to enhancement with blood reagents. Following treatment with blood reagents, it became increasingly difficult to determine whether the enhanced mark was a genuine blood print or a latent fingermark exposed to diluted blood. Latent fingermarks exposed to whole blood often resulted in a void prior to enhancement, but following treatment with blood reagents, were difficult to distinguish from a genuine blood mark enhanced with blood reagents.     

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 a comprehensive 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.     

Recovery of DNA and fingermarks following deployment of render-safe tools for vehicle-borne improvised explosive devices (VBIED)

Improvised explosive devices (IED) are responsible for a significant proportion of combat and civilian deaths around the world. Given the ease with which IEDs can be made, the large quantity of explosive which can be contained within or on a vehicle, and the use of VBIED in the past (for example the 2002 Bali bombing) in terrorist activities, VBIED are an ongoing concern for Defence and law enforcement agencies. Fingermark and DNA analyses are routinely used by police and forensic analysts to identify suspects involved in illegal activities. There is limited information available on the feasibility of obtaining fingermarks, fibres, hair and DNA samples following an explosive incident, or a situation whereby an IED has been rendered safe following the utilisation of an appropriate defeat or render-safe tool. The main objective of this study was to determine if fingermarks and/or DNA (from saliva and hair samples) placed on the interior and exterior of road vehicles, and on inanimate objects (such as plastic or glass bottles), are able to be obtained and analysed following the use of a vehicle-borne IED (VBIED) render-safe tool on a vehicle containing simulated explosives. The identification of fingermarks on the exterior (67.2±8.5%) and interior (43.8±17.8%) of the vehicles was possible following the use of the render-safe tool, though this was more challenging in the latter than the former. Fingermarks were also able to be identified from both plastic and glass bottles placed inside the vehicles. Polymerase chain reaction (PCR) techniques yielded DNA profiles that were able to be identified from saliva and hair samples. These preliminary results suggest that both fingermarks and DNA profiles, obtained from vehicles that have been subjected to a VBIED render-safe tool, may be used to identify persons of interest.     

Storage effects on ninhydrin-developed fingerprints enhanced by zinc complexation

A study has been made of the effects of storage on the fluorescence of latent fingermarks on paper developed with ninhydrin and zinc chloride. Exposure to sunlight or xenon arc light causes fading of the marks but the presence of moisture or high humidity results in the loss of fluorescence and the formation of a red non-fluorescent compound.     

Four novel alkyl 2-cyanoacylate monomers and their use in latent fingermark detection by mid-infrared spectral imaging

Four novel alkyl 2-cyanoacrylate monomers (alkyl=1-cyanoethyl, 2-cyanoethyl, trideuteromethyl and pentadeuteroethyl) have been tested for their ability to develop latent fingermarks that can then be visualized using mid-infrared spectral (chemical) imaging. Each of the four monomers was chosen for its potential to produce a strong, isolated infrared spectral band in its corresponding polymer (to provide spectral contrast against most backgrounds), as well as for its potential ability to be fumed onto fingermarks in the manner of conventional ethyl 2-cyanoacrylate (superglue). With the exception of the 2-cyanoethyl 2-cyanoacrylate, which had to be fumed under reduced pressure, all of the monomers were found to be sufficiently volatile to be fumed in a conventional fuming cabinet. All four monomers polymerized selectively on fingermark ridges on a variety of non-porous and semi-porous surfaces, leading to excellent development of the fingermarks. Unfortunately, although high quality mid-infrared spectral images of the fingermarks could be formed for all of the polymers at various frequencies, the new CN or CD stretching vibrations did not give rise to strong enough absorption intensities for good contrast on difficult backgrounds such as polymer banknotes. However, in the 1-cyanoethyl 2-cyanoacrylate polymer, the presence of the additional nitrile group had the unintended but desirable effect of shifting the strong CO absorption to higher frequencies, moving it away from interfering banknote absorptions. This enabled fingermark contrast to be achieved even against the intaglio printing on the banknotes.     

An investigation into the enhancement of fingermarks in blood on fruit and vegetables

A number of studies have reported the successful enhancement of latent fingermarks on fruit and vegetables. A study was set up to identify the most effective technique for the enhancement of fingermarks in blood on various fruit and vegetables. The enhancement techniques targeted different components in blood and consisted of protein stains (e.g. acid black 1), peroxidase reagents (e.g. leuco crystal violet) and amino acid stains (e.g. ninhydrin). Different variables such as the ageing periods of the marks and a diminishing series were employed to assess the suitability and sensitivity of the enhancement techniques.Overall, the use of different protein stains appeared to be the most effective techniques for the enhancement of fingermarks in blood on fruit and vegetables. In addition, the aubergine and cucumber skins appeared to be the most responsive surface to the different chemical techniques during enhancement. On the contrary, little or no enhancement was achieved for fingermarks in blood on the nectarine fruit.     

A Small Population Study on Friction Skin Ridges: Differences in Ridge Widths Between Latent and Inked Fingerprints

Morphological changes in the width of latent fingermark ridges occur naturally over time. This could be used to examine the aging process of latents and eventually estimate time of deposition. In a crime context, it is common practice to compare a questioned (aged) fingermark with a database of known (inked) prints. Therefore, in the absence of fresh fingermarks for aging purposes, it is of interest to reveal correlations between these two categories of fingerprints with regard to the widths of their ridges. The present study explores correlations of ridge widths between flat and rolled inked prints with latent fingermarks visualized with carbon black (CB) and titanium dioxide (TiO₂)-based powders among a small population of ten donors. Results revealed consistent differences between the ridge widths of latent and inked prints as well as flat and rolled impressions. Latent fingermarks visualized with CB and TiO₂ powders showed ridges with comparable widths.     

An efficient strategy to detect latent fingermarks on metallic surfaces

The aim of this work is to use metal sputtering for the development of latent fingermarks on metallic surfaces by taking advantage of the prints' topography. In order to promote the preferential deposition onto fingerprints' ridges the deposition parameters should be optimized. After a previous selection, copper and gold thin films were deposited by magnetron sputtering onto stainless steel substrates where fingermarks were intentionally placed. After optimizing the deposition parameters, the influence of the fingermarks' age was studied. The quality of the developed fingermarks was evaluated visually and through optical and scanning electron microscopy. The morphology of the copper and gold thin films was examined by high resolution scanning electron microscopy. The preferential magnetron sputtering deposition of copper and gold thin films, 20-30 nm thick, allows latent fingermarks to be successfully developed. The gold films are more promising, especially for detecting non-fresh fingermarks and for conserving the developed marks. It was possible to detect the contours of the ridges and localize minutiae features in a one-month aged impression developed by gold deposition. These films present discontinuous surface and columnar cross-sections, while copper thin films have a featureless morphology.     

Evaluation of a Hot Print System for the development of latent fingermarks on thermal paper: A pseudo-operational trial

Enhancement of latent fingermarks on thermal paper poses a number of problems when using traditional methods used for porous substrates due to blackening of the thermal layer as a result of polar solvents present within the reagents and high temperatures oxidising the acid/dye complex. Thus, methods which prevent such reactions are favoured for the development of latent prints on said substrates. A comparative pseudo-operational trial using UV, Hot Print System (HPS), ninhydrin and ThermaNIN was performed on 1000 thermal paper substrates gathered from various sources. The results indicated that the most effective method was an acetone pre-wash followed by ninhydrin. The sequence of HPS-ninhydrin was similarly effective when compared to ninhydrin as a sole technique. ThermaNIN produced fewer marks than ninhydrin but was superior to HPS. Whilst the HPS developed some fingermarks, there was only a very small number of marks uniquely developed by it.     

Enhanced Visualization of Latent Fingermarks on Rough Aluminum Surfaces Using Sequential Au and Zn/ZnS/ZnO Depositions

Detection and visualization of fingermarks on rough and diffuse surfaces is a relatively challenging task. We succeeded in developing latent fingermarks on scratched and rough aluminum surfaces by sequential deposition of a thin layer of gold followed by one of zinc or zinc‐based compounds on the fingermarks. The best image enhancement was achieved with sequential Au and ZnS depositions. Using this combination, we could enhance the visualization of latent fingermarks aged over 65 days in normal conditions. The optical reflectance from the fingermarks with the deposited layers of metal/dielectric is analyzed as a stratified medium. Significant contrast in the reflectance from the regions of the ridges and the valleys of the fingermark would enhance the visualization. Our results show that the Au and ZnS bi‐layer combination can have a large reflection contrast and improved fingermark visualization at wavelengths corresponding to the green light for specific thickness of ZnS.     

Transfer of nitroglycerine to hands during contact with commercial explosives

The techniques of thin-layer chromatography, gas chromatography with electron capture detection, and gas chromatography/mass spectrometry were used to analyze hand swab extracts for the presence of nitroglycerine. Both the amount of nitroglycerine transferred to the hands after handling commercial explosives and its persistence were measured. Gas chromatography-electron capture detection was found to be the most accurate and sensitive technique for making such determinations, especially if the extract was partially purified by thin-layer chromatography prior to analysis. The lowest limit of detection was 10 ng of nitroglycerine, and residues could be detected over 20 h after handling the raw explosive.     

Investigation of hydrogen cyanide generation from the cyanoacrylate fuming process used for latent fingermark detection

Cyanoacrylate fuming is one of the most common techniques employed for the detection of latent fingermarks on non-porous surfaces such as plastic and glass. The technique is generally applied by exposing items of interest to the vapours generated by heating a suitable quantity of commercial cyanoacrylate adhesive. In this study, the potential for highly toxic hydrogen cyanide (HCN) to be generated from the overheating of cyanoacrylate was investigated. Two commercial cyanoacrylate adhesives and two quantitative methods for the determination of HCN were employed: (i) the sodium picrate method; and (ii) the picrate-resorcinol method. (13)C nuclear magnetic resonance (NMR) analysis was used to confirm the presence of cyanide. In addition, the thermal decomposition of cyanoacrylate was studied using simultaneous thermogravimetric and differential thermal analysis (TGA-DTA). It was determined that detectable and quantifiable amounts of HCN were generated from the thermal decomposition of cyanoacrylate monomer and polymer at temperatures as low as 200 °C. Using an optimised picrate-resorcinol method, it was shown that around 10 μg of HCN could be generated from the heating of 1g of cyanoacrylate monomer at 200 °C. For one of the adhesives tested, this increased to above 100 μg of HCN when 1g of cyanoacrylate monomer was heated at 280 °C. Recommendations are provided that, if followed, should ensure that the cyanoacrylate fuming process can be safely applied with minimal risk to the operator.     

Development of Latent Fingermarks from Rocks and Stones

Since the beginning of recorded history, stones have been used in the commission of crimes due to their widespread availability. Stones can be used as a lethal weapon that sometimes might be the only evidence in a serious case. The common perception, even in professional fingermark circles, is that stones do not yield identifiable latent fingermarks. The authors of this research paper examined the feasibility of developing fingermarks from seven types of stones using three latent fingermark techniques: magnetic powder, cyanoacrylate fuming, and ninhydrin. The paper will demonstrate that by classifying stones and rocks according to their natural properties (porosity, permeability, and the nature of surface area), even application of the simplest development techniques can produce good results. In conclusion, chert and limestone yielded the most qualitative and quantitative results using magnetic powder. The time factor is also important in recovering latent fingermarks on stones and rocks.