Optimization of a Statistical Algorithm for Objective Comparison of Toolmarks

Due to historical legal challenges, there is a driving force for the development of objective methods of forensic toolmark identification. This study utilizes an algorithm to separate matching and nonmatching shear cut toolmarks created using fifty sequentially manufactured pliers. Unlike previously analyzed striated screwdriver marks, shear cut marks contain discontinuous groups of striations, posing a more difficult test of algorithm applicability. The algorithm compares correlation between optical 3D toolmark topography data, producing a Wilcoxon rank sum test statistic. Relative magnitude of this metric separates the matching and nonmatching toolmarks. Results show a high degree of statistical separation between matching and nonmatching distributions. Further separation is achieved with optimized input parameters and implementation of a “leash” preventing a previous source of outliers—however complete statistical separation was not achieved. This paper represents further development of objective methods of toolmark identification and further validation of the assumption that toolmarks are identifiably unique.     

Objective Analysis of Impressed Chisel Toolmarks

Historical and recent challenges to the practice of comparative forensic examination have created a driving force for the formation of objective methods for toolmark identification. In this study , fifty sequentially manufactured chisels were used to create impression toolmarks in lead (500 toolmarks total). An algorithm previously used to statistically separate known matching and nonmatching striated screwdriver marks and quasi-striated plier marks was used to evaluate the chisel marks. Impression toolmarks, a more complex form of toolmark, pose a more difficult test for the algorithm that was originally designed for striated toolmarks. Results show in this instance that the algorithm can separate matching and nonmatching impression marks, providing further validation of the assumption that toolmarks are identifiably unique.     

Angular Determination of Toolmarks Using a Computer‐Generated Virtual Tool

A blind study to determine whether virtual toolmarks created using a computer could be used to identify and characterize angle of incidence of physical toolmarks was conducted. Six sequentially manufactured screwdriver tips and one random screwdriver were used to create toolmarks at various angles. An apparatus controlled tool angle. Resultant toolmarks were randomly coded and sent to the researchers, who scanned both tips and toolmarks using an optical profilometer to obtain 3D topography data. Developed software was used to create virtual marks based on the tool topography data. Virtual marks generated at angles from 30 to 85° (5° increments) were compared to physical toolmarks using a statistical algorithm. Twenty of twenty toolmarks were correctly identified by the algorithm. On average, the algorithm misidentified the correct angle of incidence by ?6.12°. This study presents the results, their significance, and offers reasons for the average angular misidentification.     

Bullet Trajectory after Impact on Laminated Particle Board

When reconstructing a bullet's trajectory prior to impact using the spatial orientation between two consecutive bullet defects (e.g., by probing), it is important to take the bullet's deflection into account. The (critical) ricochet angles as well as the vertical and horizontal deflection angles of eight cartridge types on laminated particle board have been studied. For all eight of the cartridge types combined, the critical ricochet angles lie between approximately 14° and 26°, while for the subgroup of the jacketed bullets, this range lies lower, between approximately 14° and 18°. The data from this study can be used to assess the accuracy and precision of the applied method. The results show that the highest deflection angles are seen near the critical ricochet angle. Generally speaking, vertical and horizontal deflection angles can almost be neglected above angles of incidence of 30° or 40° for handgun ammunition when shooting at laminated particle board.     

Confocal microscopy analysis of breech face marks on fired cartridge cases from 10 consecutively manufactured pistol slides

Recent publications from the National Academy of Sciences have called for additional foundational research in the field of firearm and toolmark analysis. We examined test fires from 10 pistol slides with consecutively manufactured breech faces. A total of nine test fires from each pistol slide, for a total of 90 test fired cartridge cases, were compared using confocal microscopy combined with three-dimensional cross-correlation analysis algorithms. A total of 8010 comparisons were performed (720 matches and 7290 nonmatches). The average score for matches was 0.82 with a standard deviation of 0.06. The average score for nonmatches was 0.20 with a standard deviation of 0.03. Additionally, subclass toolmarks were observed on the breech faces, but the presence of subclass was not detected in the correlation analysis. There was no overlap of scores between matching and nonmatching test fires. This provides objective data that support the AFTE (Association of Firearms and Tool Mark Examiners) theory of identification.     

Validation of Tool Mark Comparisons Obtained Using a Quantitative,Comparative, Statistical Algorithm

Abstract: A statistical analysis and computational algorithm for comparing pairs of tool marks via profilometry data is described. Empirical validation of the method is established through experiments based on tool marks made at selected fixed angles from 50 sequentially manufactured screwdriver tips. Results obtained from three different comparison scenarios are presented and are in agreement with experiential knowledge possessed by practicing examiners. Further comparisons between scores produced by the algorithm and visual assessments of the same tool mark pairs by professional tool mark examiners in a blind study in general show good agreement between the algorithm and human experts. In specific instances where the algorithm had difficulty in assessing a particular comparison pair, results obtained during the collaborative study with professional examiners suggest ways in which algorithm performance may be improved. It is concluded that the addition of contextual information when inputting data into the algorithm should result in better performance.     

Sex and age diagnosis by ischium morphometric analysis

The growth of four variables of the ischium was analysed by polynomial regression in order to evaluate its significance and its capacity for age and sex determination during and after growth. The material used was 327 specimens ranging from birth to 97 years of age from four documented west European collections. The growth curves were calculated for ischium length and three new variables of the acetabular surface (horizontal diameter of ischium acetabular surface, vertical diameter of ischium acetabular surface and ischium acetabular index). All curves, except those of the female series of vertical diameter of ischium acetabular surface and its index, showed a lineal growth corresponding to vertical variables. All variables studied, except the ischium acetabular index, can be used variables for adult sexual discrimination. Furthermore, ischium length and the horizontal and vertical diameters of the acetabular surface can be useful for sub-adult age determination in archaeological samples, as well as in forensic samples. However, the ischium length is the best variable, as it can be applied to all the growth ages.     

The study and forensic significance of drill bit use indicators

Abstract:  A case study involving an improvised pipe bomb with a drilled fuse hole is presented. This case study and its accompanying research details drill bit use and/or nonuse indicators. These indicators are then further classified to develop relevant conclusion criteria. These criteria are: (1) trace deposits in the form of particulate and/or smears on the drill bit, especially inside the flute and the tip area, (2) physical damage including chipping, abrasion, and fissuring on the drill bit which mostly occurred on the flute edge bevels and lip edges, and (3) thermal damage. One or any combination of these indicators could be used as effective criteria for concluding drill bit usage. This study also determined that a drill bit produces well-defined toolmarks on swarf shavings that could be identified back to that particular tool, and there is no mechanical break-in period for obtaining reproducible toolmarks on newly manufactured or unused bits.     

Improve Toolmarks' Impressions in Soft Wax

When the forensic toolmarks laboratory receives for examination and comparison a tool that is suspected of having been involved in a crime, the expert performs tests designed to determine whether or not the specific tool generates the same toolmarks as those found at the crime scene. This is performed by testing tool striation on a piece of soft metal, such as lead, and examining the marks left by the tool. Studies have shown that wax may be an optimal material for this purpose. This study examines the use of wax at different temperatures and shows that quality of results is better when the wax is cooled (recommended temperature is ?18°C). At this temperature, the wax is flexible enough but does not smear and is not sticky. This makes the obtained marks clearer and of better quality.     

书写能力的结构

目的提出人的书写能力由基础因子构成的假说。方法根据因子说,不同字的笔顺可能相关。以反犬旁、山字为目标字,收集799份有效实验样本,分性别检验实验样本中2个目标字的笔顺是否相关。结果统计检验表明反犬旁笔顺与山字笔顺相关（p〈0.01）,用一个笔顺在另一个笔顺出现的条件下的出现率与它的出现率之比测定它们相关性的大小,最高的比值为3.65。结论证实了人的书写能力由基础因子构成的假说,这个假说可以作为笔迹比较的理论基础。     

条条与块块关系下的法院院长产生

条块关系是不同于西方学术典范的解释中国现象的中国叙事框架。在中国政治语境中,较之中央地方关系更重要的是条条与块块关系。在地方法院院长产生的问题上,作为块块的上级党委和本级党委与拟任职法院的上级法院之间,对人选各有不同支配关系。在武装夺权年代确立的"块块为主,条块结合"的地方治理机制,在市场经济条件下获得新的政治考量意义。     

The Class Characteristic Mark of the H&M Mul‐T‐Lock Picking Tool in Toolmarks Examination

Mul‐T‐Lock is a high security lock cylinder distinguished by the use of a telescoping “pin‐in‐pin”—tumbler design. Picking the Mul‐T‐Lock cylinder with a traditional picking tool is highly complicated because it can get stuck between the inner and outer pins. The H&M Mul‐T‐Lock picking tool was designed to overcome this problem and facilitate the picking of the “pin‐in‐pin” cylinder. The purpose of this research is to determine whether H&M Mul‐T‐Lock picking tool leaves class characteristic mark and whether it can be distinguished from traditional picking tools marks and from regular key marks. It also describes and determines the class characteristic mark left on telescopic pins, its origin, recurrence, and its benefit to the toolmarks examiner. When receiving a Mul‐T‐Lock from a crime scene, a toolmarks examiner can quickly determine whether or not it was picked by an H&M Mul‐T‐Lock picking tool by noticing the class characteristic mark which this typical tool leaves.     

Application of a computer assisted image analyzer to the assessment of area and number of sites of dental attrition and its use for age estimation

A simple method was devised to assess dental attrition in terms of its area and number of sites by using dental plaster casts and a computer assisted image analyser. The changes presented on the occlusal surfaces of teeth were investigated for age estimation using these criteria. The area of attrition on each tooth demonstrated a significant positive correlation with age, but a wide individual variation was observed in the values for each tooth. Therefore, this method was unsuitable for accurate age estimation of a single tooth. A strong negative correlation with age was observed in the number of sites of attrition. A multiple stepwise regression analysis using the variables 'attrition area' and 'attrition number' revealed multiple correlation coefficient values of 0.93. The quantitative assessment of both horizontal and vertical factors of dental attrition would be essential to improve the accuracy of this method.     

An ideal material for the preparation of known toolmark test impressions

Traditionally, toolmark test exemplars are produced by applying a tool's working surface to a piece of soft metal such as lead. Soft, pliable metals are primarily used for this purpose because they will replicate the microscopic grooves present on a tool's working surface without damaging the tool. In this paper the authors present an alternative material for the preparation of test toolmarks. Jewelry modeling or carving waxes are utilized in this study. These waxes are designed for the jewelry modeling industry to create very fine, highly detailed wax models of jewelry pieces that will be cast in various metals utilizing the lost wax casting method. Jeweler's waxes have been found to be ideal for preparing test toolmarks from exemplar tools. The test tool's working surface is applied to a piece of the appropriate wax in a manner consistent with the tool's design. The replicas obtained are exact, highly detailed, 1:1, negative impressions of the exemplar tools working surface, have a long shelf-life, and are suitable for use in toolmark examination and comparison cases.     

Forensic Comparison of Soil Samples Using Nondestructive Elemental Analysis

Soil can play an important role in forensic cases in linking suspects or objects to a crime scene by comparing samples from the crime scene with samples derived from items. This study uses an adapted ED‐XRF analysis (sieving instead of grinding to prevent destruction of microfossils) to produce elemental composition data of 20 elements. Different data processing techniques and statistical distances were evaluated using data from 50 samples and the log‐LR cost (C_llr). The best performing combination, Canberra distance, relative data, and square root values, is used to construct a discriminative model. Examples of the spatial resolution of the method in crime scenes are shown for three locations, and sampling strategy is discussed. Twelve test cases were analyzed, and results showed that the method is applicable. The study shows how the combination of an analysis technique, a database, and a discriminative model can be used to compare multiple soil samples quickly.     

Use of RGB values in the Periodic Acid-Schiff color test to determine the presence of vaginal fluid

This study demonstrates how RGB color values from microscopic smears stained with the Periodic Acid-Schiff reagent under standardized microscopy conditions can be used to indicate the presence of vaginal secretions. Based on data obtained in the study, a numeric threshold determined from the sum of separate values for red, blue and green was determined to differentiate vaginal-based samples with other body fluids. Using this threshold, 55 of 57 vaginal-based samples tested positive for the presence of vaginal secretion. Conversely, 27 of 29 smears prepared from other body fluids yielded negative results. However, when graphing RGB sum values against a calculated RGB integer no overlap in data was obtained between all vaginal-based samples and other body fluid samples, clearly differentiating them. One-way ANOVA testing with a 95% confidence interval indicated that vaginal samples from different age groups showed no difference in RGB sum values. Similarly, the location that vaginal swabs were collected (from the outside of a condom or a vaginal swab) also showed no statistical difference using one-way ANOVA at 95% confidence. Furthermore, refrigerated test swabs aged up to 15 months showed no demonstrable differences. Pair-wise t-testing using RGB sum values, however, did show significant differences between vaginal samples and all other body fluids tested. Finally, the method successfully differentiated between pre-and post-coital penile swabs and finger swabs taken before and after digital vaginal penetration in anecdotal comparisons using the method.     

Development of a Mobile Toolmark Characterization/Comparison System

Since the development of the striagraph, various attempts have been made to enhance forensic investigation through the use of measuring and imaging equipment. This study describes the development of a prototype system employing an easy‐to‐use software interface designed to provide forensic examiners with the ability to measure topography of a toolmarked surface and then conduct various comparisons using a statistical algorithm. Acquisition of the data is carried out using a portable 3D optical profilometer, and comparison of the resulting data files is made using software named “MANTIS” (Mark and Tool Inspection Suite). The system has been tested on laboratory‐produced markings that include fully striated marks (e.g., screwdriver markings), quasistriated markings produced by shear‐cut pliers, impression marks left by chisels, rifling marks on bullets, and cut marks produced by knives. Using the system, an examiner has the potential to (i) visually compare two toolmarked surfaces in a manner similar to a comparison microscope and (ii) use the quantitative information embedded within the acquired data to obtain an objective statistical comparison of the data files. This study shows that, based on the results from laboratory samples, the system has great potential for aiding examiners in conducting comparisons of toolmarks.     

The Use of Near‐Infrared Photography to Image Fired Bullets and Cartridge Cases

An imaging technique that is capable of reducing glare, reflection, and shadows can greatly assist the process of toolmarks comparison. In this work, a camera with near‐infrared (near‐IR) photographic capabilities was fitted with an IR filter, mounted to a stereomicroscope, and used to capture images of toolmarks on fired bullets and cartridge cases. Fluorescent, white light‐emitting diode (LED), and halogen light sources were compared for use with the camera. Test‐fired bullets and cartridge cases from different makes and models of firearms were photographed under either near‐IR or visible light. With visual comparisons, near‐IR images and visible light images were comparable. The use of near‐IR photography did not reveal more details and could not effectively eliminate reflections and glare associated with visible light photography. Near‐IR photography showed little advantages in manual examination of fired evidence when it was compared with visible light (regular) photography.     

An evaluation of measurement uncertainty of trajectory angles using a 3D laser scanner

Measuring trajectory angles of bullet defects at a crime scene is an important part of crime scene investigation as these angles can be used for shooting incident reconstructions. The Washington State Patrol Crime Scene Response Team (WSP CSRT) had a desire to report and use measured trajectory angles. To report quantitative measurements, a statement of uncertainty for the measurement must also be reported due to an accreditation requirement through the ANSI National Accreditation Board (ANAB), through which the WSP CSRT is accredited. This evaluation examined the measurement uncertainty of the 3D laser scanning method that the WSP CSRT utilizes for measuring the vertical and azimuth angles from trajectory rods fitted to bullet defects. Three studies were performed which examined the variation of vertical and azimuth angle measurements from trajectory rods on flat surfaces, the variation of azimuth angle measurements from a trajectory rod on a curved surface, and a traceability study with known vertical and azimuth angle measurements. Seven common substrates were selected as target materials and were shot with 9 mm Luger and 0.45 Auto caliber bullets. A vehicle with one bullet defect was utilized for the curved surface study. The WSP's current fleet of Trimble X7 3D laser scanners, the WSP Criminal Investigation Division (CID) Detectives who operate these scanners, and the Forensic Scientists responsible for trajectory rod placement and angle measurements were utilized. An overall measurement uncertainty of +/− 2.6 degrees at an approximate 95% confidence interval was determined for all trajectory angles measured from trajectory rods.     

Deciphering indented impressions on plastic

The questioned document laboratory is often called upon to decipher writing that has been erased, obliterated, or that has faded. In cases like these, the original writing is no longer legible to the naked eye, but may be enhanced using various light sources. Certain remnants of the ink's components absorb into the substrate's fibers and can be visualized, usually as luminescence or absorbance. A case is described here that involved the theft of a credit card. An empty plastic credit card holder was found in the possession of a suspect, and as submitted for examination. Indented impressions could be discerned on its clear plastic window and presumably originated from the credit card that had been held in the envelope. These indented impressions were deciphered in the hope that they would reveal enough details from the credit card to establish a connection between the plastic envelope and the stolen credit card. With methods generally utilized in the toolmarks and materials laboratory and the photography laboratory of the Israel Police, most of the indented impressions on the plastic were deciphered and a connection between the plastic envelope and the stolen credit card was demonstrated.