Firing Pin Marks Research Articles

Examination of the possibility to use Siamese networks for the comparison of firing pin marks.

One of the most discussed issues in forensic firearms identification is the subjectivity of conclusions. The main part of firearms examiners' work is to make a microscopic comparison of the marks on cartridge cases and bullets. In this process, examiners have to decide if the quantity and the quality of the observed characteristics are sufficient for identification. This decision is based on the personal experience of an examiner, so examiners with different backgrounds can come to different conclusions, and this fact presents a problem. Besides, the calculation of the error rate for this type of examination is a debatable issue. Different mathematical and statistical models were proposed, and computer-based algorithms were developed in order to avoid subjectivity and to determine error rates. This article investigates the possibility to use methods of machine learning for the comparison of marks of the firing pin impressions on cartridge cases. In the research, the Siamese network model, which included two similar Convolutional Neural Networks, was prepared and trained. For the training and validation of the model, the database of firing pin impressions was prepared. This database included images of cartridge cases discharged from 300 firearms that came from regular casework and clone images used for data augmentation. The model was trained and examined using the validation part of the database. The metrics, such as accuracy, sensitivity, and specificity were calculated. The results of the research show the possibility of using the Siamese network for building an objective forensic firearms examination system with a known error rate.

Классификация изображений следов бойков по экземплярам оружия с помощью полносвязной нейронной сети

Introduction. The aim of the work is to increase the efficiency of identification of firearms by images of firing pin marks in the automatic mode. The relevance of the task is determined by the low efficiency of the known methods of automatic identification of firearm by the firing pin marks with individual topological types of individualizing features. This affects the investigation of crimes related to the use of firearms. Formation of clone images. A training sample was formed; it included 140 original images of firing pin marks from 50 classes, on the basis of which about 1000 clone images were made with slightly modified individualizing features. In this case a specific specimen of a firearm is meant as a class. Neural network training. A fully connected neural network with the following architecture was used as a classifier: an input layer of neurons; two hidden layers; an output layer. The input layer included 2500 neurons, the first hidden layer was made up of 625 neurons, the second hidden layer contained 156 neurons; the output layer consisted of 50 neurons (in accordance with the number of the classes). Evaluation of the calculation results. The prediction accuracy of the trained neural network was estimated according to the Accuracy metric, which is the ratio of the number of correct predictions to the total number of predictions. The prediction accuracy for the maximum signal on one output neuron was 81%, and when the maximum signals on three output neurons were taken into account, the accuracy was about 91%. Conclusions. The research has shown the possibility of classification of the images of firing pin marks by weapons using a fully connected neural network, as well as the effectiveness of using artificially generated clone images of firing pin marks for training a fully connected neural network in cases with a small number of initial objects.

Comparison and interpretation of impressed marks left by a firearm on cartridge cases – Towards an operational implementation of a likelihood ratio based technique

Firearm examination is subject to increased scrutiny regarding its foundational validity and inherent subjective nature. The increased use of automatic comparison systems may help to reduce subjectivity. In this paper, we present the performance and limits of an automatic comparison system that assigns a weight to the forensic findings for the comparisons between firing pin marks, breechface marks, or a combination of the two. This weight is expressed by a likelihood ratio (LR) based on 3D topographical measurements coupled with a bi-dimensional statistical model.As the performance of such systems may depend on the reference databases used to inform the model, we investigated the impact of the brand of ammunition and the number of samples.We show that reference databases used to calculate LRs should ideally consist of the same type of ammunition as is seen in the case under investigation and that 7 specimens fired by the same firearm are enough to obtain rates of misleading evidence of a similar magnitude compared to those obtained when far more specimens (60) are used.Additionally, the automatic system was used to assess the outcomes of 7 cases with known same-source or different-source ground truths. These cases were also examined by 8 qualified firearm examiners. In all cases, the experts’ appraisals were in line with the ground truth. The automatic system showed some limitations in cases were the data were not sufficient to calculate a robust LR, but also that it can assist and enhance the examiners in their decision process.

GROUP IDENTIFICATOIN OF CARTRIDGE CASES DISCHARGED FROM HOMEMADE SUB-MACHINE GUNS

The increasing number of homemade sub-machine guns in caliber 9 mm Parabellum received for examination, as well as cartridge cases discharged from this weapon, made it necessary to single out the marks which can be used for group identification. The article gives the results of generalizing and systematization of marks observed during the examinations made in the laboratory. This work singles out the marks and traces which can be observed on the cartridge case surface and can be used for the identification of the type and model of the firearm. The construction features of homemade sub-machine guns were investigated. Among these features are the construction based on open bolt mechanical scheme, the use of static firing pin, methods of barrel assembling and fixing into the body of the weapon, which can lead to the appearance of a hole in the chamber, etc. The article also shows the influence of the tool processing on leaving special marks and traces on the breach face. These marks can also be used for the group identification. Based on the results of the research the article distinguishes between the main signs, which can be used for group identification, the sings similar to the ones known in factory-made weapons and the signs typical of homemade firearms. The first group consists of the marks of ejector and the extractor cutouts and the firing pin mark. For these sings the article describes special characteristics which makes it possible to distinguish them from the marks commonly observed on the factory-made examples. To the marks typical of homemade sub-machine guns can be applied breach face marks, cartridge case deformation, caused by differences between the sizes of the chamber and the cartridge, cartridge deformation while shooting when the cartridge case is not supported by the chamber, perforation of the sidewall of the cartridge case, etc. The article also discusses the issue of cartridge case comparison and individual identification. Great variety of the traces and marks as a result of low-quality tool processing was revealed. This can be the factor which makes comparison more difficult. However, the big number of individual marks observed on the cartridge cases makes it possible to come to well-grounded conclusion. Key words: cartridge cases, submachine guns, type and kind of weapon, expert practice.

Comparison of Shooting Trace Mark for Identification of Shooting Gun

총기 사고에서 중요한 감정분야 중 하나인 탄피흔적 시험법을 확립하고자 쌍안비교현미경의 3D 다초점 기능을 이용하여 탄피흔적 중 격침흔 계측방법 및 식별 기준을 제시하였고 CAL-45 권총 1정과 K-2 소총 4정을 이용하여 각각의 총기로 10회씩 발사된 탄피시료에 대하여 계측법을 적용하여 유사율을 확인하였다. 또한, CAL-45 권총과 K-2 소총으로 발사된 탄피시료에 대한 계측값의 유사율을 비교함으로써 탄피의 흔적감정 시 동일 총기에서 발사되었는가에 대한 판단기준으로서의 적합성을 확인하였다. K-1A 소총과 K-2 소총에서 발사된 탄두 강선흔의 기울기를 측정 비교한 결과, 두 소총간의 강선흔 기울기는 약 2도 이상 차이 남을 확인 할 수 있었다. 본 연구를 통하여 총기 발사흔 계측 데이터를 통계적으로 분석하여 기존의 총기 발사흔 감정 시 식별과정 표현의 난해함이 해소될 것으로 생각되며 향후 총기발사흔 감정에 대한 신뢰성 있는 실험과 데이터베이스 구축의 기반이 되었다.To establish a method of examining the impressions on cartridge cases, one of the most important areas of examinations in firearm accidents, measurements of firing pin marks and identification standards for analyzing impressions of cartridge cases are proposed through the use of 3D multi-focusing function of the binocular comparison microscope. Additionally, the degree of similarity has been verified by applying the measurements to the sample cartridge cases that has been fired once each by 1 CAL-45 pistol and 4 K-2 rifles. By comparing the similarity of measurements of the sample cartridge cases fired by both the CAL-45 pistol and K-2 rifle, the validity of the standard of judgment for determining whether a cartridge case has been fired from the same firearm has been verified. The slope angle of the rifling impression bullet marks of K-2 rifle are different(two degrees) from each other has been found that. Through statistical analysis of the measured data, this method diminishes the difficulty of expression that existed in the previous method of identifying shooting trace marks. Conclusively, this method serves as foundation for establishing a method of examination and a database for reliable and credible examination of shooting trace marks.

A Case Study on Identification of Firearm by Firing Pin Mark

A Case Study on Identification of Firearm by Firing Pin Mark

重み付き積算平均型Hough変換による薬きょう発射痕の特徴領域の検出

重み付き積算平均型Hough変換による薬きょう発射痕の特徴領域の検出

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.