TraceBase; A database structure for forensic trace analysis.

A data structure is proposed that can store forensic data obtained by experts from different disciplines and acquired using different instruments. This data structure, called TraceBase, is congruent with the forensic examination in the laboratory. We describe the design as well as its planned introduction in casework. The back-end of TraceBase is based on PostgreSQL and can be accessed by front-end applications such as the open-source LibreOffice office suite. The back-end regulates the flexible and robust storage of data, as well as the relation between items, samples, and analyses. The front-end applications allow the user to enter or retrieve data in an easy fashion, while the modular structure ensures that different aspects, such as the data entry, the processing and reporting of entered data, can be optimised individually. Additional analyses can be introduced and linked to items or samples already present. The database is designed such that data from several sources, different forensic disciplines and data acquired by different analytical techniques can be entered. When data needs to be retrieved for further analysis, a subcollection can be filtered for use in a specific situation.

Extraction of the relevant population from a forensic database.

Evaluation of forensic evidence using Bayesian statistics requires the formulation of hypotheses. Many hypotheses, especially those presenting the defence viewpoint imply that traces can be attributed to an arbitrary member of a relevant population. The exact items or persons that comprise the relevant population may vary from case to case. Therefore, the statistical evaluation of evidential value based on databases cannot make use of a fixed set of items or persons. In the current paper, methodology is presented to filter the contents of a database such that only items that are considered relevant are selected. Six scenarios, including those related to fibre, textile, and glass evidence are described, together with the hypotheses and relevant populations that may be evaluated by an expert. In addition, we show how items representing the defined relevant population can be extracted from a database using SQL code. Images of the items in the (filtered) relevant population provide an overview of the selected items and hence direct feedback to the examiner. In this way, erroneous codes or unwanted side effects can be identified and corrected. It is concluded that the filtering procedure is effective in cases where the relevant population is demarcated accurately.

Application of dye analysis in forensic fibre and textile examination: Case examples.

Seven cases and a quality assurance test are presented. In these cases, fibres or textiles submitted for investigation were analysed by HPLC-DAD-MS to identify the dyes present. The cases presented illustrate that it is possible to identify textile dyes in fibre traces recovered for forensic analysis. The results show that a mixture of dyes is present in all textiles investigated, except one sample that was taken from a manufacturer dye shade card. It is concluded that dye analyses improves the evidential value of forensic fibre examinations, as it becomes possible to distinguish textiles that are different in dye chemistry, but have a similar colour. In addition dye analysis makes the examination more robust, as it becomes possible to attribute colour differences between samples to identical dyes (mixed in different ratios) or to chemically different dyes.

Combined recovery of biological and fibre traces.

We present a method in which DNA and fibre traces are jointly recovered by taping. The DNA traces are isolated by standard laboratory procedures. Fibre traces are isolated afterwards in order to improve efficiency. Two tests have been carried out to evaluate the suitability of the presented method. In the first test, possible changes in appearance of fibres due to the DNA isolation procedures are investigated. In the second test, the recovery of fibres from a contaminated surface and their possible loss due to the DNA isolation procedure are investigated. It is concluded that polyester fibres are hardly affected by the DNA isolation procedure. In contrast, a relatively large number of the investigated cotton fibres were altered. The observed differences do not indicate a structural damage to the fibre or the dyes, but rather the washing-out of some components. The observed changes may require that fibres from a known source are also exposed to the DNA isolation procedures to assess the induced changes, but do not prevent a meaningful comparison. The recovery of fibres is slightly lower than the routine procedures for fibre recovery. Therefore, it was decided to perform extra taping of the recipient in cases where fibre investigation is requested. During DNA-isolation, some of the fibres present are released from the tapes. These fibres are not lost however, as they can be found on the filter in the used DNA isolation vials.

Tracers as invisible evidence - The transfer and persistence of flock fibres during a car exchange.

This study assessed the recovery of flock fibres used as a tracer in a car exchange scenario. Flock fibres were deposited onto a car seat (or model thereof) and their transfer and persistence was investigated after a real or simulated car exchange. The overall aim of this study was to achieve an optimal use of flock fibres as tracers, i.e. to be able to select a fit-for-purpose flock fibre, to be able to predict the amount of flock fibres to be recovered from crime related items, and to be able to use these numbers to exclude accidental uptake. The effect of a number of variables on the transfer and persistence of flock fibres was studied, including flock fibre length, car upholstery, and trousers material. Laboratory based experiments were undertaken first, followed by realistic field based experiments. The flock fibres were captured in a non-destructive manner through fluorescence photography. A Matlab algorithm enabled fast automated counting of flock fibres on the images. Results indicate that an initial rapid loss of flock fibres from garments may be expected as a result of moderate movement. Although the amount of flock fibres to be recovered is affected by the flock fibre length, the type of car upholstery, and the type of trousers materials (if frictional force is taken into consideration), large numbers of flock fibres have been recovered from all target materials throughout the transfer route. These numbers are higher than the amount of flock fibres recovered due to accidental uptake. In conclusion, flock fibres can serve as invisible evidence to reconstruct a series of events.

On the recovery of fibres by tape lifts, tape scanning, and manual isolation.

The recovery of fibre traces via tape lifting, tape scanning and manual isolation is investigated. The recovery efficiency of taping was determined using different tapes, donor textiles, and receptor textiles. It was determined that tape lifts generally recover over 90% of extraneous fibres that had been transferred by direct contact with a donor textile. The recovery via tape scanning was evaluated by the preparation of a set of 15 tapes that contained a number of target fibres on a background of other fibres. The tapes presented varying difficulty and were investigated by trained fibre examiners. The examiners were asked to locate the target fibres and to provide their opinion on the difficulty of the search. As expected, the efficiency decreases for more difficult searches. It was determined that the efficiency of the search was influenced by the microscopic illumination modes used by the examiner. A final experiment investigated the recovery by manual isolation of fibres from non-textile items. It was determined that all fibres from tie cables and knives were recovered, except in those cases where the recipient item contained many fibres. In addition, the examiners correctly sampled each of three fibre populations present on a sample of duct tape.

Understanding the visibility of blood on dark surfaces: A practical evaluation of visible light, NIR, and SWIR imaging.

Bloodstains on dark surfaces are often difficult to detect due to a lack of contrast. Infrared photography is in many cases a solution as it enhances the contrast between blood and background. Still, on some surfaces bloodstains cannot be visualized. In this study, we investigate why bloodstains on certain surfaces are not detected and how visibility can be improved. Bloodstains on 166 dark fabrics were photographed by four different cameras and for each, the visibility of the bloodstains was scored. The spectral properties of the dark fabrics were examined as well as the properties of the dyes used to colour the textiles. In addition, spreading of the blood within the textile and the roughness of the material were taken into account. In the investigated set of textiles, visibility of blood is mainly determined by the spectral properties of the textile dye. In addition, a high surface roughness of the textile reduces the visibility.

Spectrometric imaging of polarization colors and its application in forensic fiber analysis.

A hyperspectral imaging instrument analyzing fibers between crossed polarizers spectrometrically is presented. The principle of operation is introduced and illustrated briefly by the theory of polarization and birefingence and calculations based on Stokes parameters and Müller matrices. Afterward, the developed instrumentation and results are detailed. Results obtained by the calculations and developed instrumentation indicate that the retardance of birefringent materials can be calculated over a high range and with a high accuracy. In addition, the spatial resolution of the instrument suffices to analyze different regions within a fiber individually. This allows the selection of a region at the center of an analyzed fiber that is shown to provide an optimal signal. The developed software enables analysis of the polarization color and the "normal", i.e., absorptive color of the sample individually. These features make possible a preliminary identification of fibers, without isolation of the fiber from a microscope slide. The instrument forms a powerful new approach to automated analyses in forensic fiber evidence, as it can establish analyses of morphology, color, and identity of a set of samples in a high-throughput, automated, and objective way.

Towards source level evaluation of the evidential value of fibre examinations.

This paper aims to provide the first steps towards a numerical source level evaluation of fibre evidence. For that purpose, likelihood ratio equations are derived for four generic scenarios, in which the source frequency, the number of references and trace types investigated, and the number of matches vary. Previous experimental studies into the evaluation of fibre evidence are reviewed and we demonstrate how the results of these studies, as well as other data, can be used to evaluate the derived equations for the four scenarios. Evaluation is not straightforward and requires a number of assumptions. This is mainly because the relevant population under consideration in a specific case cannot be sufficiently evaluated. In addition, the subjective match-criterion in current forensic fibre examinations makes it impossible to implement a good evaluation of the within-variation of samples. As a result, the discrimination power, currently calculated for discrimination studies, is only valid for samples with negligible heterogeneity. We conclude that reporting a numerical evidential value for forensic fibre examinations is not yet feasible as the data are available for only a few types of fibres and cannot be used without several assumptions. We propose a number of developments that are required to improve the accuracy and numerical analysis.

Recovery of spray paint traces from clothing by beating.

Manual recovery of spray paints from textiles using a microscope, the routine method in many laboratories, is often laborious. Beating the clothing with a plastic rod, the routine method used for recovery of glass traces within the authors' laboratory, is proposed as an alternative. The efficiency of the method was evaluated by spray tests with fluorescent paint. In these tests, paint particles in the acquired debris samples, as well as those remaining on the textiles, were investigated. The results show that beating is an efficient way to recover and concentrate paint particles. A good efficiency for jeans fabric and rough knitwear is reported. The results appeared to be less satisfactory for smooth woven fabric. Application of the method in casework was effective for graffiti paints as well as for flaked car paint.

Quantitative comparison of striated toolmarks.

A comparison of striated toolmarks by human examiners is dependent on the experience of the expert and includes a subjective judgment within the process. In this article an automated method is presented for objective comparison of striated marks of screwdrivers. The combination of multi-scale registration (alignment) of toolmarks, that accounts for shift and scaling, with global cross correlation as objective toolmark similarity metric renders the approach robust with respect to large differences in angle of attack and moderate toolmark compression. In addition, a strategy to distinguish between relevant and non-relevant spatial frequency ranges (geometric details) is presented. The performance of the method is evaluated using 3D topography scans of experimental toolmarks of 50 unused screwdrivers. Known match and known non-match similarity distributions are estimated including a large range of angles of attack (15, 30, 45, 60 and 75°) for the known matches. It is demonstrated that the system has high discriminatory power, even if the toolmarks are made at a difference in angle of attack of larger than 15°. The probability distributions are subsequently employed to determine likelihood ratios. A comparison of the results of the automated method with the outcome of a toolmark comparison experiment involving three experienced toolmark examiners reveals, that the automated system is more powerful in correctly supporting the hypothesis of common origin for toolmarks with a large difference in angle of attack (30°). In return, the rate of toolmark comparisons that yield incorrect support for the hypothesis of common origin is higher for the automated system. In addition, a comparison between estimating known match and known non-match distributions using 2D and 3D data is presented and it is shown that for toolmarks of unused screwdrivers, relying on 3D is slightly better than relying on 2D data. Finally, a comparison between estimating known match and known non-match distributions for two different types of screwdrivers suggests, that the method may be used for comparing marks of other tools as well.

Identification of dyes on single textile fibers by HPLC-DAD-MS.

An HPLC-DAD-MS method is described to analyze textile dyes in different dye classes (reactive, basic, acid, direct, disperse). The described method is sensitive enough to analyze single fibers with a length of a few millimeters or less, which makes it suitable for forensic analyses. The current paper describes the information content of the acquired data as well as the results of a validation study, in which the repeatability, specificity, and limit of detection of the method were assessed by repeated measurements of nine different dyes in the mentioned dye classes. The mass accuracy (deviation generally <2 ppm) and absorbance spectra were found to be highly stable in several measurements over a period of 8 weeks. Deviation in retention times were observed and attributed to small experimental effects and a precolumn blockage. The results show that dye analysis is possible for most fibers with a minimum length of one or a few millimeters.

Simultaneous FTIR spectroscopic imaging and visible photography to monitor tablet dissolution and drug release.

PURPOSE: Previous studies of hydroxypropyl methylcellulose (HPMC)-based tablet during exposure to water showed a number of 'fronts' moving into the tablet but led to contradictory interpretations. These fronts are related to water penetration into and dissolution of the tablet, but the exact nature can not be derived from visible photographic evidence. A method to study tablet dissolution simultaneously by Fourier transform infrared-attenuated total reflection (FTIR-ATR) imaging and macro-photography can assist in providing correct interpretation of the observed fronts. METHODS: Therefore, the combination of macro-photography and FTIR-ATR spectroscopic imaging was developed and used to interpret the physical changes leading to the observed fronts. Buflomedyl pyridoxal phosphate (BPP), a coloured drug, was used as a model drug. RESULTS: The quantitative results obtained by FTIR-ATR imaging enabled the attribution of the three observed fronts (inside to outside) to: (1) true water penetration, possibly combined with (partial) dissolution of buflomedyl pyridoxal phosphate (BPP); (2) total gellification of HPMC; (3) erosion front. CONCLUSIONS: The method to study dissolution of a tablet simultaneously by FTIR-ATR imaging and macro-photography has been developed and used to obtain reliable interpretation of the fronts observed during tablet dissolution.

Release of poorly soluble drugs from HPMC tablets studied by FTIR imaging and flow-through dissolution tests.

Spectroscopic imaging and a flow-through dissolution test have been combined to improve the possibilities of investigating the release of a poorly soluble drug (diclofenac) from pharmaceutical tablets. The presented methods aim to overcome the limitations that impede the conventional dissolution test because of its inability to observe precipitates of poorly soluble drug during tablet dissolution. The proposed flow-through set-up allows small drug particles that are being carried along in the water-flow to be analyzed, by adding a dissolution agent to the medium after it left the tablet cell. Fourier transform infrared-attenuated total reflection (FTIR-ATR) spectroscopic imaging provides an insight into the processes inside the tablet and is not hindered by insoluble or recrystallising drug. The techniques have been hyphenated and used to study tablets containing diclofenac sodium and HPMC (hydroxypropyl methylcellulose) in different dissolution media that influence the solubility of the drug. The release profiles obtained by flow-through dissolution test suggest the presence of particles (or precipitates) in the dissolution medium. This is consistent with the results obtained by FTIR imaging, which confirms that both proposed techniques are superior to the ordinary dissolution test when applied to poorly soluble drugs. FTIR imaging data have been analyzed by a classical least squares analysis, corrected for the parts of the tablet outside the field of view, and used to calculate the release profile. The infrared spectra of diclofenac at varying relative humidity were acquired to study the interactions of diclofenac and water, including identification of dissociated diclofenac, thus the chemical specificity of FTIR imaging was fully utilized.

Validation of macroscopic attenuated total reflection-Fourier transform infrared imaging to study dissolution of swelling pharmaceutical tablets.

Macroscopic attenuated total reflection (ATR) infrared imaging is applied to study the dissolution of realistically sized hydroxypropyl methylcellulose (HPMC) tablets. The water intake into in situ compacted tablets and pre-compacted tablets was studied as a function of compaction pressure. Rigorous analysis of the imaging datasets show that the speed of water intake into HPMC tablet is approximately 4 microm/min and is hardly affected by the studied range of compaction pressures or the type of ATR crystal used (diamond or ZnSe). This constant speed of water intake implies that leakage (''creeping'') of water into the space between the tablet and the ATR crystal does not occur. It is shown that the radius of the HPMC tablet initially expands to twice the original radius due to swelling.

Combined approach of FTIR imaging and conventional dissolution tests applied to drug release.

A new method is developed to study drug release using a combination of FTIR imaging and conventional dissolution tests. FTIR imaging in attenuated total reflection (ATR) mode allows simultaneous measurements of the distribution of different components in the tablet, e.g., drug, polymer and water as a function of time. These imaging measurements were carried out in a combined compaction and flow-through cell, which was linked to a UV detector to quantify the amount of dissolved drug. In this way, changes in drug concentration in the aqueous solution can be studied similarly to the conventional dissolution test. This combination provides quantitative information of changes in both the tablet and the liquid phase. A tablet composed of hydroxypropyl methylcellulose (HPMC) and niacinamide was prepared and analysed using this setup. Mathematical processing of the measured spectra with a partial least squares (PLS) calibration was utilised for accurate quantitative analysis of the concentrations of different components. The results of FTIR imaging and the dissolution test are compared.

Identification of pigments in paint cross sections by reflection visible light imaging microspectroscopy.

A setup for reflection visible light imaging microspectroscopy (VIS-imaging) as well as its evaluation and application is described and tested. The spatial resolution of the system is approximately 1 microm at a spectral resolution of 4 nm. The optical contrast between different colored particles in the surface of a sample is optimized with a new image processing method for mapping of the distribution of the identified pigment particles. The potential of VIS-imaging in the study of paint cross sections obtained from paintings is explored. Spectra obtained from pigment particles in these cross sections result in classification or identification of several pigments. The investigated paint samples are challenging test cases, as they contain several colored materials with a very fine distribution. VIS-imaging can identify and map the most common traditional blue pigments, i.e., smalt, azurite, ultramarine, and indigo in 17th century oil paintings. Smalt can be identified even after complete discoloration. VIS-imaging analysis assisted in the identification and mapping of modern synthetic red and yellow pigments in a 20th century painting.