ABSTRACT: Latent fingerprints are valuable pieces of evidence that are often found when a crime has been committed. This type of evidence is hardly visible so the application of techniques to make it more visible is necessary. Furthermore, latent fingerprints can be found in wet environments, and these surfaces can be wet by water from several sources that differ in their pH and particulate matter, such as rain, roadside, canal or sea water. Small Particle Reagent (SPR) is an advantageous technique for latent fingerprint detection on wet surfaces. In this study, surface samples were moistened by soaking in various solutions to represent water from different sources. Eleven formulae of SPR, three (SPR I, II, III) from the published references and eight new modified ones, were investigated to evaluate the optimal formula for latent fingerprint detection on wet non- porous surfaces. The best quality of developed latent print was obtained from the SPR containing molybdenum disulfide in tergitol NP-7 and choline chloride. However, on a dark surface, the best quality was obtained from a suspension containing zinc carbonate as small particles. The soaking solutions used in this study did not affect the effectiveness of SPR. Nevertheless, the salt solution affected the fingerprint impression.
Key words: Latent fingerprint, SPR, small particle reagent, wet-non porous surfaces
INTRODUCTION At a crime scene, most of the information (evidence) can be used to provide information for evaluating what did or could not have happened and involving whom. Fingerprints are a type of evidence that are often found at crime. Unique characteristics, and the unchanged friction ridge of each individual’s skin over their life renders the ability to use fingerprints to identify the individual concerned. There are two general types of fingerprint evidence that can be found at the crime scene or on objects related to it that is the visible and the latent fingerprint, but they are not mutually exclusive. This study is mainly concerned with latent prints.
Latent fingerprints are not often left in heterogeneous or protected environments, so there is the need to be able to detect their presence on different surfaces and after they have undergone the action of atmospheric agents or have been found, for example, on objects soaking in water of different types of impurities and sediments. Small particle reagent (SPR) is a physical development technique for fingerprint detection on wet or moist surfaces.(1) There are many formulae of SPR available nowadays but the optimal formula has never been reported. In this study, the best SPR- formula for detecting latent fingerprints on wet non- porous surfaces was demonstrated.
*Correspondence to:- e-mail: scsrr@mahidol.ac.th
……………………………………………………………Phatwalan Kabklang, Suda Riengrojpitak and Wiwan Suwansamrith
60 J. Sci. Res. Chula. Univ., Vol. 34, No. 2 (2009)
In fact, there are many conditions of water that can contact with the fingerprint containing material surfaces, such as water from rain, roadside, effluent, canal or sea. The water from each source is quite different in its pH, salt types and levels and suspended particulate matter. However, the effect of the pH or salt concentration of the soaking solution upon the ability of each SPR to detect latent fingerprints has never been investigated. In this study, various types of surface samples soaked in each different solution (tap water, weak acid, weak base, and various concentrations of sodium chloride), which represents water from some of the different available sources, was used to evaluate the effect on latent fingerprint detection by SPR.
MATERIALS AND METHODS Eleven formulae of SPR solutions, three (SPR I, II, III) from the references2,3) and eight new modified ones, were prepared. Each formula was different in its salt and particles used, such as MoS2, Fe3O4, TiO2, ZnO and ZnCO3, so as to create different contrasts. In addition, the proportion of particle and detergent was also varied in order to evaluate the best results. The fingerprints were impressed on each set of the non-porous surface samples (glass, metal plate, plastic and ceramic) before or after soaking in various soaking solutions. Soaking solutions evaluated were: acetic acid pH 5.5, NaOH pH 8.0, NaCl solutions at 10, 30, 50 and 70% (w/v), and tap water, and were used for 30 min. All surface samples with fingerprints were sprayed with each formula of SPR in order to compare its effectiveness, and left until the fingerprint developed (2- min). The fingerprints were washed gently with distilled water, left to dry and photographed with a digital camera. Then, they were lifted by a tape lift, analyzed and compared.
RESULTS When dark particles in the SPR were used, the best quality of developed latent print on the wet surface was obtained from SPR II for every type of soaking solution. SPR II contains molybdenum disulfide, tergitol NP-7 and choline chloride, with a proportion of particles and detergent at 13.1. The fingerprint image was nearly complete (moderate), and had a ridge count of 12.98 (Tables 1 and 2). Next the quality of developed latent print obtained from SPR III (10.25) was quite similar to that of SPR II (12.98). Nevertheless, SPR III is suitable for latent print detection on glass surfaces; providing a ridge count of 14.85 (Table 1). Poor results were obtained from SPR XI, where only a poor image with a low ridge count was obtained 1.21 (Table 1). SPR I and VII could not be used to develop latent fingerprints on any type of the tested surfaces.
With respect to the use of white particles, no moderate or better quality images were obtained, only poor partial images. Within this the best quality was obtained from SPR VI with a ratio of zinc carbonate and tergitol NP-7 of 12.5 (Table 2). Moreover, SPR VI was quite effective at developing latent fingerprints on metal surfaces (Table 1). Poor results were obtained from SPR IV, V, VIII, IX, X and XI, with average ridge counts on every type of surfaces of between 0.35 and 1.75 (Table1). The soaking solvents such as tap water, acid, base and salt solutions did not affect the effectiveness of SPR suspension; but a high salt [50% and 70% (w/v)] concentration affected the fingerprint impression. Latent prints on glass surfaces prior to soaking in various solutions and after development with SPR II are shown in Figure 1.
DISCUSSION From this study, the best quality of developed latent prints on wet non-porous surfaces in every type of soaking solution was obtained from SPR II, which contains molybdenum disulfide particles in 0.8% (v/v) tergitol NP-7 (detergent), and 1.05% (w/v) choline chloride, and the proportion of particles to detergent of 13.1. The average number of ridge counts obtained was 12.98 which is sufficient to allow identification of a given individual from the fingerprint in a forensic investigation, and the fingerprint image was nearly complete (moderate, ++). When the composition of SPR II, the best in this study, and SPR III, the best formula in a previous study(3) were compared, it was found that the type of particle (MoS2) and detergent (tergitol NP-7) were similar, as were the percentages of particles, detergent and the proportion of particle to detergent. The main difference between these two formulae then was the addition of 0.4% (w/v) choline chloride to SPR II. It is plausable then that the higher number of ridge counts in the developed latent print obtained from SPR II (12.98) compared to those detected with SPR III (10.25) is due to the presence of choline chloride. The principle of SPR is based on the reaction between the fatty components in the traces and the hydrophobic tails of each specific reagent. These tails are linked to the hydrophilic heads which react with metal salt to give a precipitate.(1) Choline chloride is one such water soluble organic compound with a hydrophilic cation with the chloride anion, and a hydrophobic tail. Thus, the presence of choline chloride in SPR II may help to enhance the effectiveness of this formula by giving more attachment sites between the metal salt and the hydrophilic head based upon its polar property.
Latent Fingerprint Detection by Various Formulae of SPR on Wet Non-Porous Surfaces……………………………………...
J. Sci. Res. Chula. Univ., Vol. 1, No. 2 (2009) 61
The lowest number of ridge counts on the developed latent prints was obtained using the SPR I (0) and SPR VII (0) developers, and they could not be used to detect latent fingerprints on any type of the tested surfaces. SPR I contained 10% (w/v) molybdenum disulfide in 0.8% (v/v) tergitol NP-7, with a particle and detergent proportion of 10 and 0.8%, respectively, and a ratio of particle to detergent of 12.5. SPR VII contained ferric oxide suspended in tergitol NP-7 which could not be dissolved completely and precipitated and so fogged the background. Indeed, it has been reported before that too many particles will fog the background and too much detergent or detergent itself will degrade the latent print.(4) Thus, the percentages of Fe3O4 particle (10), detergent (0.8) and particle/detergent (12.5 g/ml) of SPR VII were similar to those in SPR I. However, the quality of the SPR formula was determined by the suitable particle and detergent components and their appropriate concentrations in the suspension. For example, molybdenum disulfide and tergitol NP-7 were used as the particle and the detergent in SPR I, II and III. SPR II and SPR III were effective solutions, with proportions of particle to detergent of 13.1 and 13, respectively, whereas that of SPR I w