Atomic force microscopy as a biophysical tool for nanoscale forensic investigations

The atomic force microscope (AFM) has found its way to the arsenal of tools available to the forensic practitioner for the analysis of samples at the nano and microscales. As a non-destructive probing tool that requires minimal sample preparation, the AFM is very attractive, particularly in the case of minimal or precious sample. To date, the use of the AFM has primarily been in the arena of imaging where it has been complementary to other microscopic examination tools. Forensic applications in the visual examination of evidence such as blood stains, questioned documents, and hair samples have been reported. While a number of reviews have focused on the use of AFM as an imaging tool for forensic analyses, here we not only discuss these works, but also point to a versatile enhancement in the capabilities of this nanoscale tool – namely its use for force spectroscopy. In this mode, the AFM can determine elastic moduli, adhesion forces, energy dissipation, and the interaction forces between cognate ligands, that can be spatially mapped to provide a unique spatial visualization of properties. Our goals in this review are to provide a context for this capability of the AFM, explain its workings, cover some exemplary works pertaining to forensic sciences, and present a critical analysis on the advantages and disadvantages of this modality. Equipped with this high-resolution tool, imaging and biophysical analysis by the AFM can provide a unique complement to other tools available to the researcher for the analysis and characterization of forensic evidence.     

Discrimination of rubber-based pressure sensitive adhesives by size exclusion chromatography

In this report, three pairs of rubber-based pressure sensitive adhesives were analyzed by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), attenuated total reflectance Fourier transform infrared spectrometry (ATR/FT-IR) and size exclusion chromatography (SEC). The size exclusion chromatograph was equipped with a refractive index (RI) detector and an ultraviolet (UV) absorption detector set to measure at 254 nm. Both adhesives of each pair revealed indistinguishable pyrograms and IR spectra, however, the SEC chromatograms were able to provide further discrimination. The differences were observed in the range below the polystyrene equivalent molecular weight of 700 Da.     

法医现场勘查学初析

法医现场勘查是公安法医检案的一个组成部分,与痕迹现场勘查各有侧重。本文通过室内、野外、运动空间三类现场初步分析了法医现场勘查的要点。     

Nano-scale composition of commercial white powders for development of latent fingerprints on adhesives

Titanium dioxide based powders are regularly used in the development of latent fingerprints on dark surfaces. For analysis of prints on adhesive tapes, the titanium dioxide can be suspended in a surfactant and used in the form of a powder suspension. Commercially available products, whilst having nominally similar composition, show varying levels of effectiveness of print development, with some powders adhering to the background as well as the print.X-ray fluorescence (XRF), analytical transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and laser particle sizing of the fingerprint powders show TiO₂ particles with a surrounding coating, tens of nanometres thick, consisting of Al and Si rich material, with traces of sodium and sulphur. Such aluminosilicates are commonly used as anti-caking agents and to aid adhesion or functionality of some fingerprint powders; however, the morphology, thickness, coverage and composition of the aluminosilicates are the primary differences between the white powder formulations and could be related to variation in the efficacy of print development.     

Soil sample metagenome NGS data management for forensic investigation

Soil analysis is a valuable resource in forensic investigation. Classical forensic soil analysis involves examination of its physical characteristics and chemical composition, such as soil type, colour, particle size, shape, pH, elemental, mineral and organic content. However the limited variability of these parameters is not always allowing adequate discrimination between soil samples. As soil supports extreme diversity of microorganisms and eukaryotic communities, microbiological approaches have been proposed. Several molecular approaches for microbial DNA profiling are available; however there is a lack of published data of implementation of the next generation sequencing (NGS) approaches for forensic soil analysis.The aim of the current study was elaboration of criteria for soil metagenome data management and database searching. We used our previously sequenced collection of 11 samples collected from different environments (forests, fields, grasslands, urban park) with different flora. The single sample collection includes 9 soil samples per one sampling area (30 m × 30 m) spaced by 15 m. In the current study we concentrated mainly on 18S rRNA gene V2-V3 region for fungi however SSU rRNA region for arbuscular mycorrhizal (AMF) fungi and V2-V3 hypervariable region of 16S rRNA gene for bacterial communities were taken into account. The sequencing was performed by Roche/454 platform. For data analysis OTU based approach on mothur software and NCBI BLASTN search were used. NCBI BLASTN analysis revealed altogether 2983 AMF matches and 8997 18S matches as well as 25477 OTUs (16S) were determined. Several data filtration approaches were used for data management. We found that 18S marker results could be used to create and run a filtered database that is computationally much more efficient and flexible. Our results have broad impact; however more samples have to be analysed, additional studies performed and cooperation between soil scientists and forensic scientists is required to be able to implement these novel techniques into the routine forensic practice.     

A forensic image processing environment for investigation of surveillance video

We present an image processing software suite, based on the Matlab environment, specifically designed to be used as a forensic tool by law enforcement laboratories in the analysis of crime scene videos and images. Our aim is to overcome some drawbacks which normally appear when using standard image processing tools for this application, i.e. mainly the lack of full control and documentation on the operations which have been performed on the images, and the absence of new, more sophisticated algorithms which can provide improved performances and "make the difference" in critical cases.     

The forensic investigation of propane gas asphyxiation

Two unusual suicides of a 19-year-old white man and a 47-year-old white man, involving propane inhalation and plastic bag suffocation, are described. The special characteristics of propane gas as an asphyxiant agent are discussed, as well as its effect on the human body. The discussion emphasizes the postmortem examination and the collection of samples for toxicologic analysis.     

海量数据取证方法的探讨

目的对当前我国电子物证检验中提取到的海量数据信息的取证难题进行探讨。方法对数据文件中海量数据信息的特点及其传统取证方法进行分析研究。结果提出开发专用工具软件进行海量数据文件的提取。结论利用专用提取工具软件可以对常见数据文件中有规律性的数据内容进行读取、计算、查重和汇总,使海量涉案数据文件的检验从传统的人工方式转变为计算机的自动处理。     

Customizing a commercial laboratory information management system for a forensic genetic laboratory

The need for high-throughput laboratories to comply with regulatory requirements makes data management an important aspect of forensic genetics. A Laboratory Information Management System (LIMS) enables efficient workflows and ensures traceability if designed and implemented properly. We customized a commercial LIMS to support STR typing of reference samples according to in-house defined requirements. The customization focused on data validity, traceability and automated solutions.     

Scanning electron microscopic analysis of skin resolution as an aid in identifying trauma in forensic investigations

The forensic investigator is frequently confronted with cases that present with wounds and blunt force trauma. Presently, the forensic investigator depends upon previous experience and further investigative deduction of the crime scene to analyze these injuries. Although not readily apparent to the naked eye, many skin tissue injuries can be visualized with scanning electron microscopy (SEM). This study was designed to establish skin trauma resolution using SEM in various skin preparations. Tissue trauma was induced on leather, preserved skin, fresh skin, and living skin using dies of varying thread size. Calibrated pressure forces in pounds per square inch (psi) were applied and impressions made using vinyl polysiloxane. Positive replicas of the tissues were prepared for SEM using isocyanate resin. After sputter coating the cast with 35 nm of gold-palladium, electron micrographs were generated using a Jeol JSM-5310LV scanning electron microscope. To establish resolution, thread widths of 52, 104, and 208 threads per inch (tpi) and trauma forces of 150, 200, and 250 psi were used to produce the impressions. Microgrooves that were identified on the die threads were analyzed. The optimum pressure for resolution studies was 150 psi using the 52 tpi die on the leather sample (4.67 +/- 0.88 microm, p = 0.046 and 0.025, respectively, by ANOVA). The resolution was compared to that of leather using preserved, fresh, and living skin. The resolution in preserved and fresh skin was less than for leather (9.00 +/- 1.73 and 10.5 +/- 4.5 versus 4.67 +/- 0.88 microm, p = 0.09 and p = 0.20, respectively). Living skin resolution was 3 microm at 52 tpi and 100 psi. Various implements of blunt force trauma were also examined using the leather sample. Time after trauma resolution was examined at 0 (3 microm), 5 (6 microm), 10 (8 microm), and 20 (9 microm) min in living tissue. A comparison between the microgrooves on the die replicas and the tissue trauma impressions revealed striking agreement for both linearity and resolution. Analysis of the microgrooves suggests that discrete morphological characteristics are seen in skin tissue traumas. This method could expand the tools available for the forensic investigation of blunt force trauma.     

A general strategy for differential forensic analysis

The dramatic growth of storage capacity and network bandwidth is making it increasingly difficult for forensic examiners to report what is present on a piece of subject media. Instead, analysts are focusing on what characteristics of the media have changed between two snapshots in time. To date different algorithms have been implemented for performing differential analysis of computer media, memory, digital documents, network traces, and other kinds of digital evidence. This paper presents an abstract differencing strategy and applies it to all of these problem domains. Use of an abstract strategy allows the lessons gleaned in one problem domain to be directly applied to others.     

中国法医学会物证专业委员会法医DNA分析的若干建议

中国法医学会法医物证学专业委员会与国际法医遗传学会中文专委会于2006年10月在成都召开学术会议。我们的讨论强调有必要将国际法医遗传学会的信息及时传递到中国。因此,按照国际法医遗传学会的指南,我们推荐混合斑分析,法医DNA数据库及新遗传标记选择标准供同行参考。     

Significance of mitochondrial DNA for forensic stain analysis, identification and forensic lineage determination

DNA testing using conventional STR systems may produce insufficient results, if the genomic DNA in the specimen is either highly degraded or the available quantity is very small (e.g. skin particles, hair shafts or ancient bones). In some of these cases the examination of mitochondrial DNA, which is present in considerably larger copy numbers in the cytoplasm, is more successful than that of nuclear DNA. Identification of unknown corpses by conventional DNA typing sometimes remains doubtful, if only samples from presumably distant relatives or putative brothers or sisters are available for comparison. Since mitochondrial DNA is generally transmitted in maternal lineages, its sequence pattern can be directly compared with those of other individuals and, in case of the same maternal lineage, corresponding sequence chromatograms are to be expected. In connection with nuclear DNA typing methods certain sequence motives may furnish clues to ethnic groups. The report presents three cases illustrating the application possibilities of mtDNA typing in forensic practice.     

Non-destructive testing techniques for the forensic engineering investigation of reinforced concrete buildings

This study describes in detail the results of a laboratory investigation where the compressive strength of 150mm side-length cubes was evaluated. Non-destructive testing (NDT) was carried out using ultrasonic pulse velocity (UPV) and impact rebound hammer (IRH) techniques to establish a correlation with the compressive strengths of compression tests. To adapt the Schmidt hammer apparatus and the ultrasonic pulse velocity tester to the type of concrete used in Algeria, concrete mix proportions that are recommended by the Algerian code were chosen. The resulting correlation curve for each test is obtained by changing the level of compaction, water/cement ratio and concrete age of specimens. Unlike other works, the research highlights the significant effect of formwork material on surface hardness of concrete where two different mould materials for specimens were used (plastic and wood). A combined method for the above two tests, reveals an improvement in the strength estimation of concrete. The latter shows more improvement by including the concrete density. The resulting calibration curves for strength estimation were compared with others from previous published literature.     

原子力显微镜在法庭科学中的应用及展望

原子力显微镜是一种具有纳米级分辨率,可观察物体表面形貌和表面结构的新型显微镜。本文对原子力显微镜的工作原理、工作模式、优点,以及原子力显微镜在法庭科学中应用进行了综述。     

Visual attention and expertise for forensic signature analysis

Eye tracking was used to measure visual attention of nine forensic document examiners (FDEs) and 12 control subjects on a blind signature comparison trial. Subjects evaluated 32 questioned signatures (16 genuine, eight disguised, and eight forged) which were compared, on screen, with four known signatures of the specimen provider while their eye movements, response times, and opinions were recorded. FDEs' opinions were significantly more accurate than controls, providing further evidence of FDE expertise. Both control and FDE subjects looked at signature features in a very similar way and the difference in the accuracy of their opinions can be accounted for by different cognitive processing of the visual information that they extract from the images. In a separate experiment the FDEs re-examined a reordered set of the same 32 questioned signatures. In this phase each signature was presented for only 100 msec to test if eye movements are relevant in forming opinions; performance significantly dropped, but not to chance levels indicating that the examination process comprises a combination of both global and local feature extraction strategies.     

A DNA microarray system for forensic SNP analysis

Forensic DNA analysis is routinely performed using polymorphic short tandem repeat (STR) markers. However, for degraded or minute DNA samples, analysis of autosomal single nucleotide polymorphisms (SNPs) in short fragments might be more successful. Furthermore, sequencing of mitochondrial DNA (mtDNA) is often performed on highly degraded or scarce samples due to the high copy number of mtDNA in each cell. Due to the increasing number of complete mtDNA genome sequences available, the limited discrimination power of an mtDNA analysis, may be increased by analysis of coding region polymorphisms in addition to the non-coding variation. Since sequence analysis of the coding region would require more material than generally present in forensic samples, an alternative SNP analysis approach is required. We have developed a one-colour microarray-based SNP detection system for limited forensic materials. The method is based on minisequencing in solution prior to hybridisation to universal tag-arrays. In a first outline of a forensic chip, a combination of 12 nuclear and 21 mitochondrial SNP markers are analysed simultaneously. The mitochondrial markers on the chip are polymorphisms within the hypervariable region as well as in the coding region. Even though the number of markers in the current system is limited, it can easily be extended to yield a greater power of discrimination. When fully developed, microarray analysis provides a promising system for efficient sensitive SNP analysis of forensic samples in the future.     

Sub-sampling and preparing forensic samples for pollen analysis

The main forensic application of palynology is in providing associative evidence, assisting to prove or disprove a link between people and objects with places or with other people. Although identification and interpretation of pollen is a specialist job, sub-sampling and preparing pollen samples for analysis may be carried out by non-specialists. As few forensic laboratories have residing palynologists, laboratories may wish to reduce the cost of analysis or risk of contamination by doing their own sub-sampling and preparation. Presented is a practical guide for sub-sampling and preparing forensic samples for pollen analysis, providing a complete standard procedure for both the palynologist and non-specialist. Procedures for sub-sampling include a wide variety of materials commonly collected for forensic analysis (soil, clothing and other fabrics, footwear, twine and rope, firearms, granulated materials, plant and animal material, and illicit drugs), many of which palynologists will not be familiar with. Procedures for preparation of samples (pollen concentration) are presented as a detailed, step-by-step method. Minimizing the risks of laboratory and cross-sample contamination during sub-sampling and preparation is emphasized.     

Choice of population database for forensic DNA profile analysis

When evaluating the weight of evidence (WoE) for an individual to be a contributor to a DNA sample, an allele frequency database is required. The allele frequencies are needed to inform about genotype probabilities for unknown contributors of DNA to the sample. Typically databases are available from several populations, and a common practice is to evaluate the WoE using each available database for each unknown contributor. Often the most conservative WoE (most favourable to the defence) is the one reported to the court. However the number of human populations that could be considered is essentially unlimited and the number of contributors to a sample can be large, making it impractical to perform every possible WoE calculation, particularly for complex crime scene profiles. We propose instead the use of only the database that best matches the ancestry of the queried contributor, together with a substantial F_ST adjustment. To investigate the degree of conservativeness of this approach, we performed extensive simulations of one- and two-contributor crime scene profiles, in the latter case with, and without, the profile of the second contributor available for the analysis. The genotypes were simulated using five population databases, which were also available for the analysis, and evaluations of WoE using our heuristic rule were compared with several alternative calculations using different databases. Using F_ST = 0.03, we found that our heuristic gave WoE more favourable to the defence than alternative calculations in well over 99% of the comparisons we considered; on average the difference in WoE was just under 0.2 bans (orders of magnitude) per locus. The degree of conservativeness of the heuristic rule can be adjusted through the F_ST value. We propose the use of this heuristic for DNA profile WoE calculations, due to its ease of implementation, and efficient use of the evidence while allowing a flexible degree of conservativeness.