Dichroism measurements in forensic fibre examination. Part 2 — Dyed polyamide, wool and silk fibres

A number of dyed polyamide, wool and silk samples were examined with plane polarized light on their dichroic behavior by optical light microscopy (OLM) and microspectrophotometry with plane polarized light (MSP-PPL). It was found that most of these acid dyed peptidic fibres possess dichroism, but these are weaker than the effects previously described for polyester fibres. The small effects may be not observed, especially for wool, but these can be measured using MSP-PPL.In the three peptidic fibre classes, for the first time, a so called “inverse dichroism” is observed which appears in the absorption spectra as a hyperchromic effect.     

Dichroism measurements in forensic fibre examination: part 5-pigmented fibres

A number of pigmented fibre samples were examined with plane polarized light on their dichroic behaviour by optical light microscopy (OLM) and microspectrophotometry with plane polarized light (MSP-PPL). It was found that about half of the samples show a strong dichroic effect and another 20% have a weak dichroism. Both regular (80%) and inversed dichroic effects (20%) occur. The dichroic characteristics of pigmented fibres can be compared to these of sheet polarizers. It is suggested that the dichroic behaviour of pigmented fibres depends strongly on the crystal structure (shape of the pigment grains) and the draw ratio (orientation of the polymer chains).     

Dichroism measurements in forensic fibre examination: Part 3 — Dyed cotton and viscose fibres

A number of dyed cellulosic fibres were examined with plane polarized light on their dichroic behavior by microscopy and microspectrophotometry (MSP-PPL). Significant dichroic effects (mostly hypochromic effects and hypsochromic bands shifts) were reported. The effect is related to the chemical structure: some dye structures always possess dichroism (azo, stilbene, thiazole and oxazine), some dyes demonstrate sometimes dichroic effects (anthraquinoid, indigoid) while other structures never demonstrate dichroic effects (sulphur, diphenylmethanes, triarylmethanes, phthalocyanines). In some cases a different dichroic behavior was found for the same dyes applied on cotton and on viscose.     

The use of linear dichroism in forensic fibre examinations — Part 6. Validation and practical aspects of MSP-PPL

This paper summarizes the results of previous work on the microscopic observation of linear dichroism found in dyed fibres (polyesters, polyamides, wool, silk, cotton, viscose, acrylics and acetates) and in pigmented fibres as well as the measurements on these fibre classes using microspectrophotometry with plane polarized light (MSP-PPL). The validation of this method is discussed and a practical tool is proposed for comparing fibre traces with control fibres. The limitations and strengths of this method are also revised.     

Inter-comparison of unrelated fiber evidence

The foreign textile fibers recovered from one item of evidence from each of 20 unrelated crimes in three categories (bank robbery, kidnapping, and homicide) were cross-compared. The items of evidence were scraped to remove the trace evidence and a sample of the collected fibers was examined using a standard scheme of analysis. The fibers were examined with light microscopy (including polarized light microscopy), fluorescence microscopy, and microspectrophotometry. The fibers were divided into natural and manufactured groups and then categorized by color and generic (polymer) class. Cross-comparing all 2083 fibers resulted in 2,168,403 comparisons, after removing duplicate (same fiber) comparisons. Colorless and denim fibers were excluded from this study. No two fibers were found to exhibit the same microscopic characteristics and analytical properties. Therefore, it is rare to find two unrelated items that have foreign fibers that are analytically indistinguishable. These results corroborate other population studies conducted in Europe and target fiber studies conducted both in the US and in Europe.     

纤维物证检验技术的现状及发展

本文概述了国内外纤维物证的发现、提取和检验方法及研究进展,并针对我国不少地区刑侦部门在现场勘查和物证检验中对纤维物证重视不够等问题,提出我国纤维物证研究应以现场发现方法、综合检验技术研究及数据库建设为主要方向。     

The random presence of glass and paint on the clothing and footwear of members of the general population: A US baseline survey at various seasons

This study assists the interpretation of glass and paint evidence by filling an existing gap in the background occurrence that reflects the socioeconomic and demographic circumstances in the United States. The collection was performed in a college US city (Morgantown, West Virginia) to determine the effect of the type of clothing worn at different seasons on the presence of glass and paint. Tape lifts and sole scrapings (1038) were collected from 210 participants and up to six clothing and footwear areas per individual. Glass fragments were analyzed via polarized light microscopy (PLM), refractive index (RI), micro-X-Ray fluorescence (μXRF), and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), while paint specimens were examined by light microscopy and infrared spectroscopy (μFTIR). Higher occurrences of glass and paint were found in the winter season. The winter collection yielded 10 glass fragments and 68 paint particles, whereas the summer collection resulted in one glass fragment and 23 paint particles. The percentage of individuals with traces varied between seasons; 7% of individuals in the winter and 0.9% in the summer had glass, whereas 36% of individuals in the winter and 19% in the summer bore paint. Lastly, when considering the overall garment and footwear areas, glass was detected in 1.4% of the winter set, compared to 0.2% in the summer collection; paint was found in 9.2% of the winter collection, whereas only 4.2% was found in the summer set. There were no instances where both glass and paint were detected on the clothing and footwear of the same individual.     

A More Efficient Method for Synthetic Textile Fiber Analysis Using Polarized Light Microscopy

The efficiency of conventional polarized light microscopy (PLM) methods for analyzing synthetic fiber evidence analyses is improved. Historically, using PLM for fiber identification relied on measuring refractive index. This prior PLM technology is reliable, but it is not efficient. Most fibers are optically anisotropic, having two principal refractive index values, N_(High) and N_(Low). When the fiber is mounted in intermediate refractive index medium, efficiency is improved by observing the change in contrast while the polarized light’s vector is rotated relative to the fiber’s axis. Minimum contrast occurs when the refractive indices of the mounting medium and fiber are equal. This angle of equality is determined by orienting the fiber’s highest refractive index parallel to the polarized light’s electric field vector, rotating the fiber or polarizing element, observing minimum contrast and measuring the angle of equality. This method is rapid, reduces remounting fibers in different mounting media and provides a quantitative measure for fiber comparisons.     

Case studies in forensic soil examinations

The examination and comparison of forensic soil samples is discussed. The origin of a simple and easy to learn procedure used and modified by the authors is reviewed. The process begins with a preliminary observation, removal of artifacts, and sieving of each specimen. A specific size fraction is split into three fractions for color matching, polarized light microscopy (PLM) examination (particle counting) and optional gradient comparison. Next, several cases are reviewed in which the modified method was used to evaluate the likelihood of common origin for questioned and known specimens.     

Particle characteristics of trace high explosives: RDX and PETN

The sizes of explosives particles in fingerprint residues produced from C-4 and Semtex-1A were investigated with respect to a fragmentation model. Particles produced by crushing crystals of RDX and PETN were sized by using scanning electron microscopy, combined with image analysis, and polarized light microscopy was used for imaging and identifying explosive particles in fingerprint residues. Crystals of RDX and PETN fragment in a manner that concentrates mass in the largest particles of the population, which is common for a fragmentation process. Based on the fingerprints studied, the particle size to target for improving mass detection in fingerprint residues by ion mobility spectrometry (IMS) is > or = 10 microm in diameter. Although particles smaller than 10 microm in diameter have a higher frequency, they constitute < 20% of the total mass. Efforts to improve collection efficiency of explosives particles for detection by IMS, or other techniques, must take into consideration that the mass may be concentrated in a relatively few particles that may not be homogeneously distributed over the fingerprint area. These results are based on plastic-bonded explosives such as C-4 that contain relatively large crystals of explosive, where fragmentation is the main process leading to the presence of particles in the fingerprint residues.     

Liver histopathology in autopsied drug-addicts

Liver specimens of 150 randomly selected autopsied drug addicts from the province of Milan (Italy) were studied using light microscopy, polarized light and immunohistochemical methods. Simple histological changes and the main diagnoses are described. The main histological diagnoses in order of frequency were: non-specific reactive hepatitis (NSRH) (52%), chronic aggressive hepatitis (CAH) (24%), acute hepatitis (AH) (12%), normal liver (6%), steatosis only (3.3%) and cirrhosis (2%). In 24 cases (16%) one or more viral antigens (HBsAg, HBcAg and Delta Ag) were detected in hepatocytes by immunohistochemical methods. Three liver specimens revealed epithelioid cell granulomas, but in no case was birefringent material identified in the liver. AH and CAH were more frequent in the group of livers with viral antigens. Our histological and immunohistochemical data confirm the current opinion that, in most cases, liver pathology in drug addicts has a viral aetiology, while no significant pathogenic role has been identified for drugs, alcohol or contaminants. Recurrent infections by one or several viruses possibly explain the relatively peculiar histological features of hepatitis in drug addicts.     

Automated Mapping of Explosives Particles in Composition C‐4 Fingerprints*†‡

Abstract: A method is described to perform automated mapping of hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine (RDX) particles in C‐4 fingerprints. The method employs polarized light microscopy and image analysis to map the entire fingerprint and the distribution of RDX particles. This method can be used to evaluate a large number of fingerprints to aid in the development of threat libraries that can be used to determine performance requirements of explosive trace detectors. A series of 50 C‐4 fingerprints were characterized, and results show that the number of particles varies significantly from print to print, and within a print. The particle size distributions can be used to estimate the mass of RDX in the fingerprint. These estimates were found to be within ±26% relative of the results obtained from dissolution gas chromatography/μ‐electron capture detection for four of six prints, which is quite encouraging for a particle counting approach. By evaluating the average mass and frequency of particles with respect to size for this series of fingerprints, we conclude that particles 10–20 μm in diameter could be targeted to improve detection of traces of C‐4 explosives.     

New Formulas to Estimate Age at Death in Maya Populations Using Histomorphological Changes in the Fourth Human Rib*

Abstract: This study develops new histomorphological algorithms for Maya populations’ human ribs and tests the applicability of published algorithms. Thin sections from the fourth rib of 36 individuals of known age were analyzed under polarized light microscopy. Osteon population density (OPD, the concentration of intact and fragmented osteons per mm²), cortical area (CA), and osteon size (OS) were recorded. Seven algorithms were calculated, using all combinations of variables, and compared to the performance of published formulas. The OPD‐based formulas deviate from the known age 8.7 years on average, while those from OS and CA deviate between 10.7 and 12.8 years. In comparison, our OPD‐based algorithms perform better than the one by Stout and Paine and much better than Cho et al. In conclusion, algorithms should be developed using OPD for different ethnic groups; although Stout and Paine’s can be used for Maya and maybe Mesoamerican individuals.     

Dr. Walter C. McCrone's contribution to the characterization and identification of explosives

Dr. McCrone was an amazing individual, possessing many talents and having many interests. He especially loved applying polarized light microscopy (PLM) to answering the question-at-hand and solving problems. He applied PLM to many different fields including the identification of air pollution particles, asbestos identification, art conservation, pharmaceuticals, industry problems and forensic sciences. A field that I believe he enjoyed the most was the characterization and identification of explosives. Throughout his life he worked on, gave presentations and published articles on the characterization and identification of explosives. Also, he encouraged other scientists to give presentations and publish on the subject by providing "behind the scene" advice and/or be a co-author on a paper. He unselfishly taught others how to apply PLM and incorporate this invaluable tool into their analytical scheme.     

微波消解-扫描电镜联用法在溺死诊断中的应用

目的探讨微波消解-扫描电镜联用法在溺死诊断中的应用价值。方法收集已知死因的尸体标本105例,其中水中尸体85例(生前溺死70例,死后抛尸入水15例),陆地自然死亡尸体20例。水中死亡案例同时收集落水处水样。分别用微波消解-扫描电镜联用法(方法 A)和硝酸破机-光镜联用法(方法 B)对上述尸体的离体肺、肝、肾、骨髓组织及水样进行硅藻定性、定量检测。结果①溺死尸体的肺、肝、肾、骨髓中及落水处水样硅藻检出率:A法分别为100%、94.3%、92.9%、82.9%、100%,硅藻检验阳性率为100%;B法分别为90%、62.9%、51.4%、28.6%、92.9%,硅藻检验阳性率为65.7%。②两种方法检出的硅藻种类与落水处水样中硅藻的种类均一致。③两种方法在死后入水尸体离体的肺中也检出少量硅藻(<3个/2g肺组织),但在死后入水尸体的其它脏器及陆地自然死亡尸体脏器中均未检出硅藻。结论微波消解-扫描电镜联用法较硝酸破机-光镜联用法对尸体离体组织脏器中的硅藻检出率高,方法灵敏,定性准确。     

Optical Characterization of Some Modern “Eco‐Friendly” Fibers*

Abstract: Fibers that are termed “eco‐friendly” or “biodegradable” by manufacturers are increasingly being used in textile products such as apparel and carpeting to appeal to the ever more environmentally aware public. As such, these modern fibers are expected to begin showing up more often in forensic casework, and it is important that the forensic examiner recognize them. This study employed polarized light microscopy (PLM) and Fourier transform infrared (FTIR) microspectroscopy to characterize selected fibers of azlon, polylactic acid (PLA), cellulose composites of alginate or chitin, and bamboo (viscose rayon). Fiber cross‐sections, refractive indices, melting points, solubilities, and FTIR measurements were conducted. Results indicate that the azlons and PLA fibers are easily distinguishable from other textile fibers by their optical and chemical properties. The cellulose composites show only small differences in comparison with other cellulose‐based fibers, while bamboo viscose rayon is indistinguishable from normal viscose rayon.     

Bicomponent acrylic fibers—their characterization in the forensic science laboratory

The increased incidence of bicomponent acrylic fibers received in this laboratory (approximately 30 samples in a five-year period) led us to investigate methods of recognizing, characterising and comparing fibers of this type. Nine varieties present in our own reference collection were examined by brightfield and polarized light microscopy, cross-sectioning, infrared spectroscopy and scanning electron microscopy. The case work samples were compared with these to see whether they reflected any additional varieties. Nearly 70% of them were Orion types, approximately 20% resembled Monsanto X-24 and only one type (encountered twice) did not correspond exactly to any reference sample. Some bicomponent fibers may be easily overlooked by normal microscopical examination. When recognised, they may be characterised into one of the various types using the methods described.     

Analysis of the possible use of liquid crystals in fingerprinting

Preliminary results concerning the use of liquid crystals (LC) in fingerprinting are given. These were based on thin layers of liquid crystals, changing colours (observed in linear polarized light) due to dissolved organic matter, transferred from fingers' surfaces. The possibility is shown of using LC to illustrate not only the surface but also the spacial configuration of a fingerprint. Relations are given between the amount of organic matter generating a fingerprint on a given surface and the coloured "response" of LC which may be used for identification as well as approximate estimation of the process of ageing.     

The Effects of Environmental Exposure on the Optical,Physical, and Chemical Properties of Manufactured Fibers of Natural Origin

Manufactured fibers derived from natural origins include viscose rayon, azlon, and polylactic acid (PLA). A 2‐year study was conducted to document any changes these fibers undergo as a result of exposure to various environmental conditions. Fabric swatches representing each fiber type were exposed to freshwater, saltwater, heat, cold, ultraviolet light, or composter conditions. Fibers from the swatches were periodically analyzed using polarized light microscopy and Fourier transform infrared microspectroscopy. Fiber solubility and melting‐point behavior were measured every 6 months. Except for the complete degradation of viscose rayon in the composter, saltwater, and freshwater environs, no changes in the optical properties, infrared spectra, solubility, or melting points of the remaining fibers in any of the environments were observed. However, microscopic morphological changes were observed in fibers from two azlon swatches submerged in freshwater and saltwater, two PLA swatches exposed to ultraviolet light, and two viscose rayon swatches exposed to ultraviolet light.     

Passport examination by polarized infrared spectra

In this study, a new nondestructive technique for passport examination is proposed. In this technique, linearly polarized light is used to measure Fourier transform infrared (FT-IR) reflectance spectra of films on the biographical data page. Thirty genuine and thirty-five counterfeit Japanese passports and five marketed films pasted on name cards were examined. The measured spectra were analyzed as follows. The absorption spectra were obtained by the Kramers-Kronig transformations of reflectance spectra. The peak ratios were then calculated from the absorption spectra by adding the peak areas at 1126 and 1263 cm(-1) and dividing the result by the peak area at 1727 cm(-1). When nonpolarized light was used, the samples could not be distinguished by comparing the peak ratios. However, when polarized light was used, they were successfully distinguished by the comparison. Therefore, polarized light is useful for the forensic discrimination of passport films by the measurement of FT-IR spectra.