Accuracy and Repeatability of Trajectory Rod Measurement Using Laser Scanners

Three‐dimensional (3D) technologies contribute greatly to bullet trajectory analysis and shooting reconstruction. There are few papers which address the errors associated with utilizing laser scanning for bullet trajectory documentation. This study examined the accuracy and precision of laser scanning for documenting trajectory rods in drywall for angles between 25° and 90°. The inherent error range of 0.02°–2.10° was noted while the overall error for laser scanning ranged between 0.04° and 1.98°. The inter‐ and intraobserver errors for trajectory rod placement and virtual trajectory marking showed that the range of variation for rod placement was between 0.1°–1° in drywall and 0.05°–0.5° in plywood. Virtual trajectory marking accuracy tests showed that 75% of data values were below 0.91° and 0.61° on azimuth and vertical angles, respectively. In conclusion, many contributing factors affect bullet trajectory analysis, and the use of 3D technologies can aid in reduction of errors associated with documentation.     

The Accuracy and Repeatability of Reconstructing Single Bullet Impacts Using the 2D Ellipse Method

When a bullet punctures a surface, it leaves behind a bullet impact, which can be analyzed in order to determine the origin and trajectory path from which a bullet was discharged using many different scientific methods to reconstruct a shooting scene. The purpose of the research was to test the accuracy and repeatability of reconstructing the impact angle of single bullet impacts using the ellipse method. The research was conducted by firing various calibers of ammunition into drywall panels positioned at varying angles of incidence from 88° until ricochet occurred. This was done in order to determine which caliber type and angle of incidence are most accurate and precise for reconstructing a shooting scene. The study examined four caliber types fired into drywall panels, with 5 repeated shots for each of the 11 angles of incidence (n = 220). Furthermore, 31 participants partook in the study to estimate a bullet impact angle of incidence utilizing the ellipse method. The results show that the best performance (accuracy and repeatability) is seen with the measurements of the 0.45 caliber ammunition. When angle of incidences is low (<64°), the performance (accuracy and repeatability) was seen to be better in all caliber ammunitions. Overall, the data provided for single bullet impacts deposited in drywall show that the ellipse method is useful in providing measurements for most crime scene reconstruction purposes and has also demonstrated that results vary depending on the type of ammunition, firearm, and angle of incidence being examined.     

Accuracy and Reproducibility of Bullet Trajectories in FARO Zone 3D

With three-dimensional (3D) laser scanning technology and software packages, the practice of documenting and measuring bullet trajectories has benefited from greater accuracy and reproducibility. This study investigated the accuracy and reproducibility of the bullet trajectory tools in the software package, FARO Zone 3D (FZ3D). Twelve participants were provided laser scanner data for 21 bullet trajectories on drywall panels with impact angles between 25° and 90°. When the impact plane was manually aligned by the operator, 75% of the absolute errors were within 0.91° and 0.98° for the azimuth and vertical angles, respectively. The vertical angle improved to 0.47° when impact plane alignment was taken with respect to gravity (no operator influence). Thus, manual alignment is shown to be subject to greater error than alignment with gravity. However, this study shows that the accuracy and reproducibility of the FZ3D bullet trajectory tools to be comparable with previous research studies.     

The systemic error in the vertical component of handgun bullet trajectory reconstructions

Establishing the path or trajectory of a fired bullet is an often recurring part of shooting incident reconstruction. The current study describes how gravitational pull causes a systemic error on the vertical component of a trajectory reconstruction. Bullet drop, drop angle, and vertical offset are explained and calculated for 10 different handgun/ammunition combinations over a range of distances up to 100 m. The presented results are intended to provide forensic firearm examiners with a reference frame for the magnitude of error introduced on handgun bullet trajectory reconstructions over distance. Threshold values of 20 and 30 m are proposed as conservative distances up to where bullet trajectories can be modeled as straight lines with subsonic/transonic handgun bullets and with supersonic handgun bullets respectively. Both the bullet drop and vertical offset will be below 5 cm at these distances for those categories. The drop angle will be below 0.3°.     

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.     

Ricochet of AK bullets (7,62 × 39 mm) on concrete and cement surfaces; a forensic-based study

The ricochet behaviour of AK bullets (7,62 x 39 mm) on two different concrete samples (rough and a cement-skimmed intermediate) and one cement sample were explored in this study. The estimated critical angles for these surfaces were shown to be 10.8° and 11.1° for the rough and intermediate concrete surfaces and 13.2° for the cement surfaces. In all occasions, fragmentation of the bullets was observed upon reaching critical angles. The results from the concrete surfaces highlighted the sensitivity of AK bullet ricochet angles from concrete surfaces with a different surface roughness and composition. Almost all resulting ricochet angles for the more frangible cement surfaces were observed to be much higher than currently reported literature would suggest. Consistent bullet wipe markings were observed on most samples, acting as a strong indicator for the directionality of the projectile during ricochet. Interestingly for the cement surface, a clear relationship was reported between the angle of incidence and the depth of the crater produced. Ultimately, this study highlights the potential uncertainties and possible errors that could occur in bullet trajectory determination from ricochet marks for this bullet and target combination if theoretic interpretations alone are used. There is no substitute for bullet and surfacespecific practical trials if the most accurate shooting scene reconstructions are to be carried out.     

A shot through the window

At issue in this case was whether an unusual window defect seen in two of the crime scene photographs was due to a bullet and if so, if that same bullet fatally wounded the victim. The window appeared to have been cracked prior to the apparent shot through it. A .22 bullet recovered from autopsy, when examined only by light microscopy, failed to show associated glass fragments. A previously cracked test window was shot a number of times with .22 caliber bullets near the cracks in an effort to simulate the window defect seen in the crime scene photographs. Several of the defects produced by the test window shots appeared similar to the crime scene window defect. The .22 bullet taken from the victim and several of the test bullets (collected by a cotton box) were examined by scanning electron microscopy/energy dispersive X-ray spectroscopy. The test bullets showed glass particles on and embedded in their surfaces. Particles of similar size and composition were found embedded in the surface of the bullet from the victim. The bullet likely struck the window prior to hitting the victim. It was apparent by the morphology of some of the mushroomed test .22 bullets that they hit the window crack. These bullets showed that the glass on one side of a crack often fails before the other side during the strike. Aggregations of powdered glass on many of the mushroomed surfaces of the .22 bullets suggest that as the bullet mushrooms during impact on the window surface, the glass in contact with the bullet powderizes and coats the mushroomed surface of the bullet with a layer of fine glass particles.     

Ricochet Behavior on Glass—Critical Ricochet Angles,Ricochet Angles,and Deflection Angles

For shooting scene reconstruction purposes, knowledge about the ricochet behavior of bullets provides valuable information. In this study, the critical ricochet angles of four cartridge types were established on plain float glass. The estimates of the critical ricochet angles varied between cartridge types and were 21.0° for .32 Auto FMJ bullets, 15.8° for 9 mm Luger FMJ bullets, 17.6° for .45 Auto FMJ bullets, and 21.3° for 9 mm Luger, Action NP bullets. The corresponding ricochet and deflection angles per incidence angle varied depending on the state of the ricocheted bullets. The mean ricochet angles are always lower than the corresponding angles of incidence, and the mean ricochet angles for the FMJ bullets with undamaged jackets are lower than those of bullets where the jacket is either damaged or the bullet partially ricocheted and partially perforated. Mean ricochet angles are lower for undamaged FMJ bullets than for undamaged Action NP bullets.     

Hierarchical,Three‐Dimensional Measurement System for Crime Scene Scanning

We present a new generation of three‐dimensional (3D) measuring systems, developed for the process of crime scene documentation. This measuring system facilitates the preparation of more insightful, complete, and objective documentation for crime scenes. Our system reflects the actual requirements for hierarchical documentation, and it consists of three independent 3D scanners: a laser scanner for overall measurements, a situational structured light scanner for more minute measurements, and a detailed structured light scanner for the most detailed parts of tscene. Each scanner has its own spatial resolution, of 2.0, 0.3, and 0.05 mm, respectively. The results of interviews we have conducted with technicians indicate that our developed 3D measuring system has significant potential to become a useful tool for forensic technicians. To ensure the maximum compatibility of our measuring system with the standards that regulate the documentation process, we have also performed a metrological validation and designated the maximum permissible length measurement error E_MPE for each structured light scanner. In this study, we present additional results regarding documentation processes conducted during crime scene inspections and a training session.     

撞击角度和速度已知条件下的球形弹丸飞行弹道轨迹算法

针对刑侦工作中弹打玻璃类案件的侦破难点,研究一种用于计算球形弹丸抛射击打玻璃案件中弹丸飞行轨迹的算法。本文以弹丸撞击角度和撞击速度为基础参数,在阐明前置基础数据的前提下,将弹打玻璃类案件中的玻璃窗分为垂直于地面及倾斜于地面两类,采用三角函数计算和参数替换的方法,通过对弹丸撞击瞬间的弹道参数设定、弹孔图像在玻璃平面内的二维图像参数设定、相关角度的描述、计算抛物线轨迹与弹道轨迹朝向等一系列步骤,最终,研究出上述两类玻璃窗的弹道轨迹计算方法。研究表明,弹丸弹道飞行轨迹算法可以还原弹丸飞行的轨迹抛物线,作为现场弹道轨迹重建系统的核心算法使用,为开发弹打玻璃类案件的现场弹道轨迹重建系统提供了关键技术。     

Prediction of Projectile Ricochet Behavior After Water Impact*

Abstract: Although not very common, forensic investigation related to projectile ricochet on water can be required when undesirable collateral damage occurs. Predicting the ricochet behavior of a projectile is challenging owing to numerous parameters involved: impact velocity, incident angle, projectile stability, angular velocity, etc. Ricochet characteristics of different projectiles (K50 BMG, 0.5‐cal Ball M2, 0.5‐cal AP‐T C44, 7.62‐mm Ball C21, and 5.56‐mm Ball C77) were studied in a pool. The results are presented to assess projectile velocity after ricochet, ricochet angle, and projectile azimuth angle based on impact velocity or incident angle for each projectile type. The azimuth ranges show the highest variability at low postricochet velocity. The critical ricochet angles were ranging from 15 to 30°. The average ricochet angles for all projectiles were pretty close for all projectiles at 2.5 and 10° incident angles for the range of velocities studied.     

Projectile entry angle determination

Small angles of projectile entry are difficult to determine in two-dimensional targets or in three-dimensional targets where internal deflection has taken place. This results from the fact that small errors in measurement lead to large errors in the calculation of the sine function used in the estimation of the angular projection of a circle onto an inclined plane at angles of less than 20 degrees from the normal. The use of a bullet tip scale, constructed to the dimensions of the entering projectile, allows a significantly more accurate determination of small angles of entry in targets not subject to stretching. A comparison of the relative error inherent in calculating entry angle using the sine function and measuring the angle using the bullet tip scale demonstrates the suitability of using the tip scale at angles less than 20 degrees and the sine function at entry angles greater than 20 degrees.     

An Empirical Study on the Relation Between the Critical Angle for Bullet Ricochet and the Properties of Wood

The properties of a bullet, an object, and the incidence angle determine whether the bullet will penetrate, perforate, or ricochet. In this study, the critical angle for ricochet was established for .32 Auto and 9 mm Luger bullets on Abachi, Southern Yellow Pine, Beech, and Ipe wooden boards. Results show that the critical angle differs depending on caliber and wood type. The critical angle is higher for .32 Auto bullets than for 9 mm Luger bullets and increases with increasing wood density and Janka hardness. The established critical angles for ricochet on the lightest and softest wood (Abachi) are 10.4° and 10.3° for .32 Auto and 9 mm Luger, respectively. For the heaviest and hardest wood (Ipe), the angles were 45.0° and 33.4°, respectively. The combined results on the four tested woods show a strong linear relationship between both the density and the hardness and the critical angle for both calibers.     

跳弹创形态学的实验研究

目的 探讨跳弹创形成的条件,研究跳弹在体内弹道学特点及致伤能力,建立跳弹创的诊断依据。方法选用国产54式手枪及56式半自动步枪,配用51式手枪弹及56式步枪弹以水磨石板为反跳靶体,射击约克夏种猪4头,复制出跳弹创模型12例。观察射入口、创道及着弹点特征。结果 跳弹的形成受靶体性状、弹头形态和速度、入射角与反跳角等条件因素的影响;在相同条件下高初速尖型弹头的反跳角<低初速圆型弹头;创道无明显瞬时空腔效应;根据实验结果建立了6项诊断依据。结论 正确诊断跳弹创对射击方向和距离、重建弹道、分析枪击目的、评估损伤程度有实用价值。     

The application of lead isotope analysis to bullet individualization in two homicides.

Bullets were characterized by lead isotope ratio analysis and trace element analysis in two homicides. In one case, we concluded that a fatal bullet did not share a common origin with bullets in a box of ammunition containing 24 cartridges taken from suspects. Evidence in the second case included two bullets from the crime scene and 163 bullets taken from various suspects. We were able to infer that the two bullets from the crime scene did not share a common origin and that they differed from all of the bullets taken from suspects. All of the suspects' ammunition had been reloaded as was evident both from trace and isotopic analysis and, indeed, from visual inspection.     

体内弹道射击角度的计算与分析

目的　推断被枪击者在中弹瞬间所处的位置和姿势以及枪支击发时的位置。方法　采用立体几何作图法和三角函数计算法进行体内弹道射击角度计算。结果　可以准确计算枪弹弹道与人体解剖学三维断面———矢状面、冠状面、水平面产生的角度。结论　可以确定被枪击者中弹瞬间的位置及体位或枪支击发时的位置 ,对分析案件性质有非常重要的法医学意义     

The Critical Angle for Perforation versus Ricochet of a .38 CAL. LRN Bullet on a Windshield

From forensic point of view, it is important to clarify the condition whether ricochet or perforate for a bullet fired toward the automobile windshield. The purpose of this study was to specify the critical angle at which the ricochet of the fired bullet takes place. To estimate the result of firing, a rigid‐body dynamics simulation of the bullet together with the test‐firing using .38 CAL. LRN bullet was examined. It was found both from numerical simulation and firing test that when the incidence angle is <45°, a complete perforation of the windshield was observed, whereas the bullet ricocheted remaining a characteristic damage on the windshield when the incidence angle is >60°. To measure the static failure resistance of various windshields, static indentation test was also examined.     

Geomatic techniques in forensic science: A review

The purpose of this review paper is to highlight various geomatic techniques that crime scene reconstructionists or forensic practitioners can use to document different kinds of scenes, highlighting the advantages, disadvantages, and when best to use each technology. This paper explores geomatic techniques such as a total station, photogrammetry, laser scanners and structured light scanners and how they can be used to reconstruct crime scenes. The goal of this paper is not to discredit manual methods, as they are long standing and reliable, but instead to shed light on alternative methods that may produce equally or more accurate results with a more visually appealing final product. It is important for law enforcement and forensic professionals to understand the advantages and disadvantages of each technique, knowing when certain techniques should be used (and when they should not), and being able to revert to traditional methods if required.