Three-Dimensional Analysis of Cartridge Case Double-Casts

Due to the shot-to-shot variability in tool mark reproduction on fired cartridge cases, a method of replication is needed for the creation of training and testing sets. Double-casting is one method that has been used for this application, but the accuracy and variability of this method needs to be characterized. Three firearms were used to fire 25 cartridges each to create the master cartridge cases. The double-casting method consists of creating a silicone mold of the master cartridge case. A plastic resin mix is then poured into the mold to create the double-cast reproduction. Fifteen double-casts of each of the 75 fired cartridge cases were created across different silicone molds to analyze within- and between-mold variability. The master cartridge cases and double-casts were scanned with a confocal microscope (Sensofar® S neox) to create three-dimensional representations of the surfaces. Two similarity metrics were used for the objective comparison of the double-casts to their master cartridge cases: the areal correlation coefficient (ACCF_MAX) and the number of congruent matching cells (CMC). The ACCF_MAX and CMC data, along with visual examinations, showed that the double-casting method produces accurate reproductions. Within-mold variability was found to be minimal, and between-mold variability was low. These results illustrate that double-casting can be applied for training and testing purposes.     

Accuracy of comparison decisions by forensic firearms examiners

This black box study assessed the performance of forensic firearms examiners in the United States. It involved three different types of firearms and 173 volunteers who performed a total of 8640 comparisons of both bullets and cartridge cases. The overall false-positive error rate was estimated as 0.656% and 0.933% for bullets and cartridge cases, respectively, while the rate of false negatives was estimated as 2.87% and 1.87% for bullets and cartridge cases, respectively. The majority of errors were made by a limited number of examiners. Because chi-square tests of independence strongly suggest that error probabilities are not the same for each examiner, these are maximum-likelihood estimates based on the beta-binomial probability model and do not depend on an assumption of equal examiner-specific error rates. Corresponding 95% confidence intervals are (0.305%, 1.42%) and (0.548%, 1.57%) for false positives for bullets and cartridge cases, respectively, and (1.89%, 4.26%) and (1.16%, 2.99%) for false negatives for bullets and cartridge cases, respectively. The results of this study are consistent with prior studies, despite its comprehensive design and challenging specimens.     

95式5．8mm自动步枪射击弹壳上痕迹的研究

目的研究95式5.8mm自动步枪射击弹壳上痕迹的检验价值。方法用10支95式5.8mm自动步枪分别射击50发,对收集的500枚射击弹壳在显微镜下观察测量。结果弹壳上痕迹反映普遍较浅,痕迹具有特殊性。结论95式5.8mm自动步枪射击弹壳上痕迹具有一定的同一认定价值。     

The Effect of pH on Electrolyte Detection of Fingermarks on Cartridge Cases and Subsequent Microscopic Examination

Cartridge cases may contain deposited fingermarks when the firearm was loaded ( http://www.nij.gov/pubs-sum/225320.htm , J Forensic Sci, 53 , 2008 and 812). Cartridge cases can be individualized with microscopic examination. However, heat and friction degrades the deposited fingermark on the fired cartridge cases, if any on the surface. Also, unfired and fired cartridge cases are made of metal, which is a nonporous surface that does not retain fingermarks well ( http://www.nij.gov/pubs-sum/225320.htm ). This study tests the effects of pH level on fingermark clarity on brass fired and unfired cartridge cases and microscopic striation examination (MSE). Two trials were performed to determine the optimal pH in fingermark clarity for both types of cartridges. This was performed through immersion in six pH range solutions from dilutions of sulfuric acid and sodium hydroxide for 24 h for the purpose of enhancing the fingermarks on the metal. The use of the optimal neutral pH level is suggested because immersion of the cartridge cases in pH 1–3 and 3–5 affects MSE.     

几种新型手枪射击弹壳上痕迹特征浅析

为了适应新形势下枪弹检验工作的需要,我中心枪弹处于1997、1998年分别购置了一批新型枪支.其中有13种配用9mm×19mm巴拉贝鲁姆手枪弹的新型手枪,它们分别是213型9毫米手枪、213A型9毫米手枪、七七B型9毫米手枪、七七B2型9毫米手枪、NP20型9毫米手枪、NP22型9毫米手枪、NP28型9毫米手枪、NP38型9毫米手枪、201C型9毫米手枪和NZ75型9毫米手枪.为了让更多的同行了解这13种新型手枪发射子弹的弹壳上的主要痕迹特征,我们制作了一些样本.由于每种枪仅购置了一支,故本文所介绍的有些痕迹特征究竟属于种类特征,抑或是个别特征,还有待于作进一步的实验和研究.将13种枪支划分为5组分别进行论述:一组:213型、213A型;     

Performance Evaluation of a Registered Ballistic Database Using the Evofinder® System

Firearms for police in China are registered along with their fired bullets and cartridge cases. A Registered Ballistic Database (RBD) of 1000 Norinco QSZ‐92 pistols with registered ammunition was established and was evaluated through the Evofinder® system. In this research, 1000 bullets and 1000 cartridge cases were randomly selected and correlated against an RBD of 2996 bullets and 2999 cartridge cases. Examiners found that successful identifications all ranked 1st, supported with land (100%), groove (97%) engraved areas, and primary marks (85.6%) for bullets, and firing pin impressions (99.8%), and breech face marks (99.9%) for cartridge cases. Two known matches (KM) for the same pistol rank in the top two (100%). The distribution of similarity scores varies from marks; however, the Evofinder® system could still effectively distinguish known matches from known nonmatches (KNM) for either bullets or cartridge cases. This study demonstrates the efficiency of the RBD.     

79式微型冲锋枪子弹射击顺序的研究

目的研究79式微型冲锋枪发射子弹的排序。方法对已知顺序实弹射击取样,扩大观察弹头、弹壳上发射过程中形成的痕迹,通过统计、归纳,从中发现与排序有关的痕迹特征。结果壳体肩部圆点痕,弹底边缘压擦痕、拉壳钩痕与发射顺序有关。结论壳体肩部圆点痕、弹底边缘压擦痕等痕迹的有无、位置及轻重程度,对判断79式微型冲锋枪弹壳发射顺序有较可靠的参考价值。     

2005式9mm警用转轮手枪射击弹壳痕迹研究

目的 研究2005式9mm警用转轮手枪射击弹壳痕迹,为警用转轮手枪射击弹壳痕迹检验鉴定提供理论依据.方法 预实验中选取10把警用转轮手枪以单动、联动方式分别射击收取弹壳样本,观察识别射击弹壳上各个痕迹的位置、形态及相互关系;补充验证实验中选取其中5把警用转轮手枪以单动方式分别进行射击实验,完善、验证预实验中得出的结论.结果警用转轮手枪射击弹壳上的烟垢痕迹、弹底窝痕迹及击针头痕迹的分布位置、形态具有规律性,具备检验鉴定价值.结论 利用弹底窝痕迹、烟垢痕迹结合击针头痕迹,可以实现射击弹壳的准确定位;利用烟垢痕迹、弹底窝痕迹及击针头痕迹具有推定弹壳先后射击顺序的可能性;通过弹底窝痕迹、击针头痕迹的细节特征比对,可以实现射击枪支的同一认定.     

Automated region segmentation on cartridge case base

One of the significant problems encountered in criminology studies is the successful automated matching of fired cartridge cases, on the basis of the characteristic marks left on them by firearms. An intermediate step in the solution of this problem is the segmentation of certain regions that are defined on the cartridge case base. This paper describes a model-based method that performs segmentation of the cartridge case using surface height image of a center fire cartridge case base. The proposed method detects the location of the cartridge case base center and specific circular contours around it iteratively by projecting the problem to a one-dimensional feature space. In addition, the firing pin impression region is determined by utilizing an adaptive threshold that differentiates impression marks form primer region surface. Letters on the cartridge case base are also detected by using surface modeling and adaptive thresholding, in order to render the surface comparison operation robust against irrelevant surface features. Promising experimental results indicate the eligibility of the proposed method to be used for automated cartridge case base region segmentation process.     

Classification of firing pin impressions using HOG-SVM

Crimes, such as robbery and murder, often involve firearms. In order to assist with the investigation into the crime, firearm examiners are asked to determine whether cartridge cases found at a crime scene had been fired from a suspect's firearm. This examination is based on a comparison of the marks left on the surfaces of cartridge cases. Firing pin impressions can be one of the most commonly used of these marks. In this study, a total of nine Ruger model 10/22 semiautomatic rifles were used. Fifty cartridges were fired from each rifle. The cartridge cases were collected, and each firing pin impression was then cast and photographed using a comparison microscope. In this paper, we will describe how one may use a computer vision algorithm, the Histogram of Orientated Gradient (HOG), and a machine learning method, Support Vector Machines (SVMs), to classify images of firing pin impressions. Our method achieved a reasonably high accuracy at 93%. This can be used to associate a firearm with a cartridge case recovered from a scene. We also compared our method with other feature extraction algorithms. The comparison results showed that the HOG-SVM method had the highest performance in this classification task.     

Statistical Approaches to Type Determination of the Ejector Marks on Cartridge Cases

While type determination on bullets has been performed for over a century, type determination on cartridge cases is often overlooked. Presented here is an example of type determination of ejector marks on cartridge cases from Glock and Smith & Wesson Sigma series pistols using Naïve Bayes and Random Forest classification methods. The shapes of ejector marks were captured from images of test‐fired cartridge cases and subjected to multivariate analysis. Naïve Bayes and Random Forest methods were used to assign the ejector shapes to the correct class of firearm with success rates as high as 98%. This method is easily implemented with equipment already available in crime laboratories and can serve as an investigative lead in the form of a list of firearms that could have fired the evidence. Paired with the FBI's General Rifling Characteristics (GRC) database, this could be an invaluable resource for firearm evidence at crime scenes.     

Evaluation of GLOCK 9 mm Firing Pin Aperture Shear Mark Individuality Based On 1,632 Different Pistols by Traditional Pattern Matching and IBIS Pattern Recognition

Over a period of 21 years, a number of fired GLOCK cartridge cases have been evaluated. A total of 1632 GLOCK firearms were used to generate a sample of the same size. Our research hypothesis was that no cartridge cases fired from different 9‐mm semiautomatic GLOCK pistols would be mistaken as coming from the same gun. Using optical comparison microscopy, two separate experiments were carried out to test this hypothesis. A subsample of 617 test‐fired cases were subjected to algorithmic comparison by the Integrated Ballistics Identification System (IBIS). The second experiment subjected the full set of 1632 cases to manual comparisons using traditional pattern matching. None of the cartridge cases were “matched” by either of these two experiments. Using these empirical findings, an established Bayesian probability model was used to estimate the chance that a 9‐mm cartridge case, fired from a GLOCK, could be mistaken as coming from the same firearm when in fact it did not (i.e., the random match probability).     

Visualisation by confocal microscopy of traces on bullets and cartridge cases

The capabilities of confocal scanning laser microscopy for the visualisation of marks on bullets and cartridge cases were investigated. Confocal microscopy provides solutions to important limitations of conventional comparison microscopy with grazing light incidence, as generally used for the examination of these marks. It is expected that confocal microscopy, thanks to its broad applicability within the field of firearms investigation and its capability of non-destructively gathering quantitative three-dimensional information, will lead to a more complete and objective forensic examination of bullets and cartridge cases.     

QSZ92式9mm手枪射击弹壳击针痕迹次种类特征的研究

目的研究QSZ92式9mm手枪击针在生产加工过程中潜在的次种类特征,以区别于个体特征。方法用超景深体式显微镜对特定工序连续生产加工的10件QSZ92式9mm手枪击针的射击痕迹进行观察比对。结果不同击针形成的击针痕迹痕底特征具有特定性,而痕壁特征中的同心圆状或圆弧状加工痕迹具有相似性,属于次种类特征。结论同一认定过程中不能将击针痕迹中的同心圆状或圆弧状加工痕迹作为个体特征使用。     

The effect of electrostatic fingerprint visualization on integrated ballistic identification systems

Visualization of fingerprint corrosion on spent brass cartridge cases by the application of a high electrical potential and conducting carbon powder is becoming an accepted method of fingerprint enhancement. However, to date, no examination has been made of any effect this technique has on ballistic identification. To resolve this, images of the breech face and firing pin marks were captured on six plated nickel and six brass primer cup spent cartridge cases. Three nickel and three brass cases were then subjected to the application of a potential of +2500 V for a period of 1 min. The remaining cases were additionally subjected to the application of carbon powder. These latter cases were then washed to remove all traces of powder. Each case was recaptured with the same ballistic identification apparatus and imaging procedure. None of the twelve cases showed any visual difference after the application of the potential or conducting powder.     

Optimizing Ballistic Imaging Operations

Ballistic imaging systems can help solve crimes by comparing images of cartridge cases, which are recovered from a crime scene or test‐fired from a gun, to a database of images obtained from past crime scenes. Many U.S. municipalities lack the resources to process all of their cartridge cases. Using data from Stockton, CA, we analyze two problems: how to allocate limited capacity to maximize the number of cartridge cases that generate at least one hit, and how to prioritize the cartridge cases that are processed to maximize the usefulness (i.e., obtained before the corresponding criminal case is closed) of hits. The number of hits can be significantly increased by prioritizing crime scene evidence over test‐fires, and by ranking calibers by their hit probability and processing only the higher ranking calibers. We also estimate that last‐come first‐served increases the proportion of hits that are useful by only 0.05 relative to first‐come first‐served.     

A Fully Automatic Method for Comparing Cartridge Case Images,

When a gun is fired, it leaves marks on cartridge cases that are thought to be unique to the gun. In current practice, firearms examiners inspect cartridge cases for “sufficient agreement,” in which case they conclude that they come from the same gun, testifying in courts as such. A 2016 President's Council of Advisors on Science and Technology report questioned the scientific validity of such analysis (President's Committee of Advisors on Science and Technology, Washington, DC, Executive Office of the President). One recommendation was to convert firearms analysis to an objective method. We propose a fully automated, open‐source method for comparing breechface marks on cartridge cases using 2D optical images. We improve on existing methodology by automating the selection of marks, and removing the effects of circular symmetry. We propose an empirical computation of a “random match probability” given a known database, which can be used to quantify the weight of evidence. We demonstrate an improvement in accuracy on images from controlled test fires.     

Repeatability and reproducibility of comparison decisions by firearms examiners

In a comprehensive study to assess various aspects of the performance of qualified forensic firearms examiners, volunteer examiners compared both bullets and cartridge cases fired from three different types of firearms. They rendered opinions on each comparison according to the Association of Firearm & Tool Mark Examiners (AFTE) Range of Conclusions, as Identification, Inconclusive (A, B, or C), Elimination, or Unsuitable. In this part of the study, comparison sets used previously to characterize the overall accuracy of examiners were blindly resubmitted to examiners to assess the repeatability (105 examiners; 5700 comparisons of bullets and cartridge cases) and reproducibility (191 examiners of bullets, 193 of cartridge cases; 5790 comparisons) of firearms examinations. Data gathered using the prevailing AFTE Range were also recategorized into two hypothetical scoring systems. Consistently positive differences between observed agreement and expected agreement indicate that the repeatability and reproducibility of examiners exceed chance agreement. When averaged over bullets and cartridge cases, the repeatability of comparison decisions (involving all five levels of the AFTE Range) was 78.3% for known matches and 64.5% for known nonmatches. Similarly averaged reproducibility was 67.3%% for known matches and 36.5% for known nonmatches. For both repeatability and reproducibility, many of the observed disagreements were between a definitive and inconclusive category. Examiner decisions are reliable and trustworthy in the sense that identifications are unlikely when examiners are comparing non-matching items, and eliminations are unlikely when they are comparing matching items.     

A survey of image processing techniques and statistics for ballistic specimens in forensic science

This paper provides a review of recent investigations on the image processing techniques used to match spent bullets and cartridge cases. It is also, to a lesser extent, a review of the statistical methods that are used to judge the uniqueness of fired bullets and spent cartridge cases. We review 2D and 3D imaging techniques as well as many of the algorithms used to match these images. We also provide a discussion of the strengths and weaknesses of these methods for both image matching and statistical uniqueness. The goal of this paper is to be a reference for investigators and scientists working in this field.     

A part-declared blind testing program in firearms examination

In 2015 and 2016 the Central Unit of the Dutch National Police created and submitted 21 cartridge case comparison tests as real cases to the Netherlands Forensic Institute (NFI), under supervision of the University of Twente (UT). A total of 53 conclusions were drawn in these 21 tests. For 31 conclusions the underlying ground truth was “positive”, in the sense that it addressed a cluster of cartridge cases that was fired from the same firearm. For 22 conclusions the ground truth was “negative”, in the sense that the cartridge cases were fired from different firearms. In none of the conclusions, resulting from examinations under casework conditions, misleading evidence was reported. All conclusions supported the hypothesis reflecting the ground truth. This article discusses the design and results of the tests in more detail.