The Use of Liquid Latex to Recover Latent Fingerprints that are Covered in Debris from Exterior Glass Surfaces of Vehicles

The purpose of this research is to determine if latent fingerprints deposited on the exterior glass surfaces of vehicles, then covered in debris, can be recovered. Past research used liquid latex to lift soot to recover trace evidence. Recently, liquid latex has been used to recover latent fingerprints along the bottom of vehicles. In this study, a total of 216 latent fingerprints were deposited on the exterior windows of three vehicles. Three control and three experimental latent fingerprints were placed on each side window. The vehicles collected debris for either 2, 3, or 4 weeks. After debris collection, liquid latex was applied to the experimental sections. The underlying fingerprints were developed with white granular powder. Control fingerprints were developed directly with white granular powder. A chi-square test revealed a significant difference in fingerprint recovery between the control and liquid latex method (X² = 9.026, d.f. = 1, p = 0.003). An odds ratio determined that the control method increases the probability of latent fingerprint recovery by 2.68. Fisher's exact test indicated that there is no statistically significant difference between the detail of the recovered control and experimental fingerprints (p = 0.065). This study demonstrates that recovery of fingerprints is possible using the liquid latex method; however, the control method recovers more fingerprints on the glass exterior of vehicles. If latent fingerprints are thought to be present on the exterior glass surfaces of vehicles, the control method should be used to improve vehicle processing by investigators.     

Application of fluorescence lifetime imaging (FLIM) in latent finger mark detection

Fluorescence lifetime imaging (FLIM) in frequency domain enables the mapping of the spatial distribution of fluorescence lifetimes of a specimen. It has been extensively applied in biology. In this paper, a theoretical analysis for the fluorescence lifetime determination of latent finger mark samples is described, which is followed by the feasibility study of using FLIM in frequency domain for latent finger marks detection. Preliminary experiments are carried out with latent finger marks treated with a fluorescent powder on two different substrates. The resulting fluorescence lifetime image of finger mark revealed a good contrast, and was able to detect the latent finger marks clearly.     

Application of fluorescence lifetime imaging (FLIM) in latent finger mark detection

Fluorescence lifetime imaging (FLIM) in frequency domain enables the mapping of the spatial distribution of fluorescence lifetimes of a specimen. It has been extensively applied in biology. In this paper, a theoretical analysis for the fluorescence lifetime determination of latent finger mark samples is described, which is followed by the feasibility study of using FLIM in frequency domain for latent finger marks detection. Preliminary experiments are carried out with latent finger marks treated with a fluorescent powder on two different substrates. The resulting fluorescence lifetime image of finger mark revealed a good contrast, and was able to detect the latent finger marks clearly.     

An assessment of the effectiveness of 5-methylthioninhydrin within dual action reagents for latent fingerprint development on paper substrates

A critical investigation of 5-methylthioninhydrin (5MTN) is presented as a 'dual action' formulation component for the development of latent finger marks on paper substrates. Preparation of a dual action reagent was performed by combining proportions of 5MTN and zinc chloride (ZnCl(2)) in a pre-mixed solution. Developed prints (deposited on filter paper substrates) could be subsequently visualised in both colour and fluorescence modes. Finger mark quality was graded using a quartered print approach for a number of reagent compositions to deliver an optimised formulation recipe. To fully appraise 5MTN in comparison to currently employed chemistries, this reagent was evaluated against three alternative amino acid selective reagents, ninhydrin, 1,8-diazafluorenone (DFO) and 1,2-indandione/ZnCl(2). Six common paper types were used for this purpose and split depletion finger marks from six donors were collected. Finger mark sets were also left for two days or two weeks to show the effect of ageing on development quality. For the first time, it was shown that 5MTN/ZnCl(2) is effective as a 'dual action' reagent under the United Kingdom climate conditions. However, results presented herein show that the existing recommended chemistries and the 1,2 indandione/ZnCl(2) process are all more effective than this new latent finger mark enhancement reagent. In a preliminary sequencing study, we show the effectiveness of the existing DFO-ninhydrin sequence over dual action reagents.     

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.     

The recovery of latent fingermarks and DNA using a silicone-based casting material

There are many techniques available for the recovery of fingermarks at scenes of crime including the possibility of taking casts of the marks. Casts can be advantageous in cases where other destructive recovery techniques might not be suitable, such as when recovering finger marks deposited on valued or immobile items. In this research, Isomark (a silicone-based casting material) was used to recover casts of finger marks placed on a variety of substrates. Casts were enhanced using cyanoacrylate fuming. Good quality marks were successfully recovered from a range of smooth, non-porous surfaces. Recovery from semi-porous surfaces was shown to be inefficient. DNA was subsequently extracted from the casts using QIAamp Mini extraction kits, amplified and profiled. Full DNA profiles were obtained 34% of samples extracted.     

Detection of nitro-organic and peroxide explosives in latent fingermarks by DART- and SALDI-TOF-mass spectrometry

The ability of two mass spectrometric methods, surface-assisted laser desorption/ionization-time of flight-mass spectrometry (SALDI-TOF-MS) and direct analysis in real time (DART-MS), to detect the presence of seven common explosives (six nitro-organic- and one peroxide-type) in spiked latent fingermarks has been examined. It was found that each explosive could be detected with nanogram sensitivity for marks resulting from direct finger contact with a glass probe by DART-MS or onto stainless steel target plates using SALDI-TOF-MS for marks pre-dusted with one type of commercial black magnetic powder. These explosives also could be detected in latent marks lifted from six common surfaces (paper, plastic bag, metal drinks can, wood laminate, adhesive tape and white ceramic tile) whereas no explosive could be detected in equivalent pre-dusted marks on the surface of a commercial lifting tape by the DART-MS method due to high background interference from the tape material. The presence of TNT and Tetryl could be detected in pre-dusted latent fingermarks on a commercial lifting tape for up to 29 days sealed and stored under ambient conditions.     

Heat and let dye: Part II – Rapid heat-fixing of blood traces

Blood-contaminated shoeprints and footmarks contain valuable operational information as they may bind an individual who stepped in the crime scene with the incident and not merely with the location. As determining the age of a bloodstain remains a challenge, while processing the scene, it is difficult to determine whether the blood is completely, or partially, dry. Thus, executing a dye staining protocol may wash these marks away as they might still be soluble. However, to meet this challenge, it is possible to fix blood marks using heat. This study aims to find a solution for floor surfaces covered by heavier blood traces (shoeprints and footmarks). For this purpose, a new pseudo-operating device was constructed for examining the blood-fixing process of both mentioned trace types. Two trials were performed with depletion marks. The results revealed that fully developed fresh and heavily blood deposits were obtained by heating to 200°C for 7.5 min using the fixing device, followed by a staining protocol using amido black solution. The achieved sharp resolution of the examined bloody prints demonstrates that in certain cases the dehydration mechanism of heating is preferred over precipitating the proteins attributed to 5-sulfosalycilic acid; thus, reducing the risk of washing blood evidence while processing the crime scene.     

血尿肝中巴比妥类药物硅藻土提取紫外差示导数光谱测定

目的建立一种操作简单、快速、去除杂质能力强、提取率高的硅藻土提取血、尿、肝中巴比妥类药物的方法。方法尿液不经稀释、血液经稀释过硅藻土柱,乙醚洗脱;肝匀浆用6%高氯酸沉淀蛋白,上清液过硅藻土柱,二氯甲烷洗脱药物。洗脱液挥干用0.45mol/L氢氧化钠溶液溶解,将溶液等分为两份,分别用等量的0.45mol/L氢氧化钠溶液和0.6mol/L硼酸-氯化钾溶液稀释,得到pH10和pH14水溶液,以pH10溶液为参比,测定pH14溶液的紫外二阶导数光谱进行药物检测。结果该法提取率血98.6%~100.3%,尿99.7%~103.2%,肝78.4%~102%,检出限均低于1.0μg/g(m l),变异系数小于2.9%,线性范围0.5~5.0μg/m l。结论硅藻土提取血、尿、肝中巴比妥类药物、紫外差示导数光谱法进行测定,适合作为法医毒物常规检验方法。     

Selective colorimetric determination of TNT partitioned between an alkaline solution and a strongly basic Dowex 1-X8 anion exchanger

The Meisenheimer anions formed from TNT in KOH solutions in alcohol or acetone were used in screening tests for TNT among possible nitro-explosives. The same reaction was used for the spectrophotometric assay of TNT in soil by CRREL (Cold Regions Research & Engineering Laboratory of the U.S. Army) method, also known as Jenkins' method, but the color stability was too dependent on the solution composition and the water tolerance was low, necessitating complete drying of soil samples (which may cause partial analyte decomposition) prior to analysis. This study reports the development of a colorimetric method based on the solid phase extraction (SPE) of the Meisenheimer anion formed from TNT and aqueous NaOH into a strongly basic anion exchange resin Dowex 1-X8 (OH(-) form). The orange-red color that developed both in the solid resin and solution phases was persistent for at least 1h. The resin was let to swell in alcohol, washed first with 1M aqueous NaOH, and then with H(2)O before use. To 5 mL of 4-400 ppm TNT solutions in 1:1 (v/v) acetone-water, 0.5 mL of 5% NaOH was added, diluted to 50 mL with 1:1 acetone-water, and the resulting solutions (containing the orange-red Meisenheimer anion of TNT) were agitated at room temperature with 0.9 g resin for < or =50 min. TNT exhibited a reasonably constant distribution coefficient between the resin and aqueous phases. The absorbance of the filtered solutions was measured against a reagent blank at 500nm. The TNT-loaded resins were regenerated with 1M HCl containing sodium sulfite. The calibration line of filtrate absorbance versus analytical concentration was linear over two orders of magnitude between 0.4 and 40 ppm TNT in final solution. Unlike Jenkins' method, the method was tolerant to 100-fold (by mass) of common soil anions like sulfate, nitrate, and chloride. The basic advantages of the developed colorimetric method over the similar CRREL/Jenkins' method may be summarized as color stability, water and common ion tolerance, lowering of the LOD, and widening of the linear range. As opposed to Jenkins' method, the charge-transfer bands characteristic to colorimetric detection were not obscured by the presence of water. The method is suitable for on-site applications, because the color developed in heterogenous solution was stabilized, and the method can be easily practiced with a portable colorimeter to large numbers of samples.     

The Use of Liquid Latex for Soot Removal from Fire Scenes and Attempted Fingerprint Development with Ninhydrin*

Abstract: Throughout the United States, clearance rates for arson cases remain low due to fire’s destructive nature, subsequent suppression, and a misconception by investigators that no forensic evidence remains. Recent research shows that fire scenes can yield fingerprints if soot layers are removed prior to using available fingerprinting processes. An experiment applying liquid latex to sooted surfaces was conducted to assess its potential to remove soot and yield fingerprints after the dried latex was peeled. Latent fingerprints were applied to glass and drywall surfaces, sooted in a controlled burn, and cooled. Liquid latex was sprayed on, dried, and peeled. Results yielded usable prints within the soot prior to removal techniques, but no further fingerprint enhancement was noted with Ninhydrin. Field studies using liquid latex will be continued by the (US) Virginia Fire Marshal Academy but it appears that liquid latex application is a suitable soot removal method for forensic applications.     

Determination of diquat in biological materials by electron spin resonance spectroscopy

An electron spin resonance (ESR) method already in use for the quantitative analysis of paraquat was applied to the analysis of diquat in blood, serum, urine, tissue homogenates and several drinks without purification of the samples. The diquat radical produced with ascorbic acid at alkaline pH was much more stable than that produced with the commonly used sodium dithionite. Radical decay in solutions covered with n-hexane was less than 5% after 60 min over a wide range of ascorbic acid concentrations. In 0.2 N NaOH solution 85% of the radicals was present even after 24 h. The limit of detection was 0.3 micrograms/ml and the required amount of sample was 0.1 ml. When both diquat and paraquat were present in a sample the diquat was first extracted with 1-butanol prior to the ESR measurement, because both species were converted to the radicals.     

A survey of some metallographic etching reagents for restoration of obliterated engraved marks on aluminium-silicon alloy surfaces

A brief survey to assess the sensitivity and efficacy of some common etching reagents for revealing obliterated engraved marks on Al-Si alloy surfaces is presented. Experimental observations have recommended use of alternate swabbing of 10% NaOH and 10% HNO(3) on the obliterated surfaces for obtaining the desired results. The NaOH etchant responsible for bringing back the original marks resulted in the deposition of some dark coating that has masked the recovered marks. The coating had been well removed by dissolving it in HNO(3) containing 10-20% acid. However, the above etching procedure was not effective on aluminium (99% purity) and Al-Zn-Mg-Cu alloy surfaces. Also the two reagents (i) immersion in 10% aq. phosphoric acid and (ii) alternate swabbing of 60% HCl and 40% NaOH suggested earlier for high strength Al-Zn-Mg-Cu alloys [23] were quite ineffective on Al-Si alloys. Thus different aluminium alloys needed different etching treatments for successfully restoring the obliterated marks. Al-Si alloys used in casting find wide applications especially in the manufacture of engine blocks of motor vehicles. Hence, the results presented in this paper are of much relevance in serial number restoration problems involving this alloy.     

Comparison of Rehydration Techniques for Fingerprinting the Deceased after Mummification

Postmortem decay causes fingertip decomposition, desiccation, shriveling, and rigidity, reducing the possibility of obtaining sufficiently clear fingerprints for identification. In this study, five rehydration solutions (ammonium hydroxide, sodium carbonate, potassium hydroxide, urea, and warm water) followed by three fingerprint recording methods (photograph, inking roll, and dusting tape) were investigated to process mummified fingertips from an unidentified cadaver. The results show that sodium carbonate treatment is the most effective for minutiae restoration, followed by ammonium hydroxide treatment. This study also demonstrates that even those fingertips that previously failed in urea solution, 1% potassium hydroxide solution, and warm water treatment could be further improved with sodium carbonate solution to obtain qualified minutiae for fingerprint matching. The optimal procedure is rehydrating the desiccated fingertips with sodium carbonate solution for 24 h followed by dusting the finger and transferring the print to adhesive tape.     

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.     

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.     

The transfer and persistence of petrol on car carpets

The significance of the presence of petrol in motor vehicle fires has often been challenged due to the possibility of a natural occurrence of petrol residues inside the vehicle. Transfer and persistence studies were undertaken to investigate the potential transfer and persistence of petrol onto vehicle carpets through the 'normal' usage of motor vehicles. The results of the transfer study indicate that petrol may be transferred from the external environment in sufficient quantities via the shoes of drivers or passengers to be detected after a 24 h period, but not after 1 week. Low levels of petrol were detectable after 24 h on all carpet mats where the initial volume was 500 microL or more. The level of evaporation of the petrol detected increased with corresponding increases in the time period between transfer and analysis. The results of the persistence study indicate that small volumes of petrol (less than 100 microL) are unlikely to be detected on carpet after a 24 h period, and volumes of less than 1000 microL are unlikely to be detected on acoustic padding after this time period. Larger volumes may be detected after this period, but will generally not be detectable on either carpet or acoustic padding after 4 weeks. In each case, the petrol that is detected exhibits a chromatographic profile of greater than 60% evaporated petrol. These results demonstrate the significance of finding a large volume of fresh or slightly evaporated petrol on car carpet.     

Background interference from car carpets—the evidential value of petrol residues in cases of suspected vehicle arson

This study was undertaken to test the theory that there is a natural occurrence of petrol on the carpet or carpet mats of motor vehicles that would interfere with the potential determination of arson residues. Part of this study was also to determine what levels of background interference due to the carpet matrix are likely to be encountered in the general population of motor vehicles. The study was conducted in three parts.

• 1.A persistence study was conducted to determine the evaporation and persistence of unleaded petrol on carpet. The results indicate that small volumes of petrol (less than 100 μl) are unlikely to be detected on carpet after a 24 h period. Larger volumes will be detected after this period, but will generally not be detectable after 1 week.
• 2.A known history study was conducted by the insertion of carpet mats, for varying lengths of time, into the driver area of separate vehicles, with subsequent analysis for the presence of petrol. A ‘history’ sheet was completed by the occupants of the vehicles during the insertion periods to record the frequency of contact with petrol, and general usage of the vehicles. The results indicate that petrol will not normally be found on previously uncontaminated carpet mats after a 6-week period of use in a vehicle, however, the occupation and behaviour of the occupants can affect the types of compounds deposited onto the carpet.
• 3.An unknown history study was conducted via the collection of carpet or carpet mat samples from vehicles with an unknown history, and subsequent analysis for the presence of petrol. Six of the 150 samples examined contained petrol. These results indicate that only a small proportion of motor vehicles will exhibit the presence of petrol on carpet or carpet mats, and then only as evaporated petrol.

All of the above findings increase the evidential value of finding significant volumes of fresh or slightly evaporated petrol on carpet products in motor vehicles.     

Examination of the steps leading up to the physical developer process for developing fingerprints

This is a systematic study that examines several acid prewashes and water rinses on paper bearing latent prints before its treatment with a silver physical developer. Specimens or items processed with this method are usually pretreated with an acid wash to neutralize calcium carbonate from the paper before the treatment with a physical developer. Two different acids at varying concentrations were tested on fingerprints. Many different types of paper were examined in order to determine which acid prewash was the most beneficial. Various wash times as well as the addition of a water rinse step before the development were also examined. A pH study was included that monitored the acidity of the solution during the wash step. Scanning electron microscopy was used to verify surface calcium levels for the paper samples throughout the experiment. Malic acid at a concentration of 2.5% proved to be an ideal acid for most papers, providing good fingerprint development with minimal background development. Water rinses were deemed unnecessary before physical development.     

Using Alkylate Components for Classifying Gasoline in Fire Debris Samples

The characteristic that discriminates gasoline from other ignitable liquids is that it contains high‐octane blending components. This study elaborates on the idea that the presence of gasoline in fire debris samples should be based on the detection of known high‐octane blending components. The potential of the high‐octane blending component alkylate as a characteristic feature for gasoline detection and identification in fire debris samples is explored. We have devised characteristic features for the detection of alkylate and verified the presence of alkylate in a large collection of gasoline samples from petrol stations in the Netherlands. Alkylate was detected in the vast majority of the samples. It is demonstrated that alkylate can be detected in fire debris samples that contain traces of gasoline by means of routine GC‐MS methods. Detection of alkylate, alongside other gasoline blend components, results in a more solid foundation for gasoline detection and identification in fire debris samples.