Forensic Firearm Examination Research Articles

Machine Learning and Possibility of its Application for Forensic Researches on Firearms

Role of machine learning in modern society cannot be over-estimated, especially given its steadily increasing importance in recent years. Various machine learning models are applied not only in everyday life but also in solving practical, engineering, and scientific challenges. However, the methods and capabilities of machine learning remain relatively obscure to most professionals across various fields of knowledge, including specialists in forensic firearm examination. The article discusses basic tasks that machine learning methods can facilitate and provides examples of tasks faced by forensic experts during firearm examinations that can be solved utilizing these methods. The article purpose is to familiarize professionals in the field of forensic science with be-sic capabilities of machine learning methods. The research paper demonstrates which specific types of tasks in forensic firearms examination it is advisable to apply these methods to, and what is required for this purpose. In order to achieve this goal, general scientific methods (dialectical, comparative, analysis, synthesis, induction, deduction) and special scientific methods (formal-logical, systemic-structural) have been employed. Specific expertise and skills in forensic identification methods (including ballistics, microscopic comparative analysis of traces on bullets and casings, detection and examination of gunshot residue to estimate shooting distance, etc.), principles of machine learning, and mathe-matical algorithms used to construct various models have been applied.

The inconclusive category, entropy, and forensic firearm identification

There has been extensive recent discussion of the difficulty in estimating meaningful error rates in forensic firearms examinations, and other areas of pattern evidence. The 2016 President’s Council of Advisors on Science and Technology (PCAST) report was clear in criticizing many forensic disciplines as lacking the types of studies that would provide error rate measurements seen in other scientific fields. However, there is a substantial lack of consensus on the approach to measuring an “error rate” for fields such as forensic firearm examination that include in the conclusion scale the “inconclusive” category, as occurs in the Association of Firearm and Tool Mark Examiners (AFTE) Range of Conclusions and many other such fields. Many authors appear to assume the error rate calculated in the binary decision model is the only appropriate way to report errors, but there have been attempts made to adapt the error rate from the binary decision model to scientific fields in which the inconclusive category is viewed as a meaningful outcome of the examination process. In this study we present three neural networks of differing complexity and performance trained to classify the outlines of ejector marks on cartridge cases fired from different firearm models, as a model system for examining the performance of various metrics of error in systems using the inconclusive category. We also discuss an entropy, or information, based method to assess the similarity of classifications to ground truth that is applicable to range of conclusion scales, even when the inconclusive category is used.

Исследование обстоятельств выстрела с помощью метода трехмерной фотограмметрии

Introduction. A promising direction in forensic practice is the use of three-dimensional modeling of objects to establish the circumstances relevant to the criminal case. Theoretical analysis. Photographs taken during the investigation could be used as a source of information to derive a three-dimensional model. Photogrammetry is a method that allows for the automated construction of three-dimensional models from images. The main data in three-dimensional photogrammetry should be the elements of external and internal orientation, coordinates in the photograph, and spatial coordinates. Еmpirical analysis. To build a three-dimensional model, photos from the crime scene submitted for forensic firearm examination were used to determine whether the situation described by the accused, suspect, corresponded to the objective mechanism of the accident. The main stages of model building in 3D photogrammetry software Agisoft Metashape were reflected. Based on the procedural documents submitted for examination, the three-dimensional model reflected the alleged location of the shooter and the victim, and the direction of the shots from the defendant’s words, as well as the likely direction of the shots in accordance with the wound channels and the situation. Discussion of results. There are essential advantages of three-dimensional photogrammetry: it does not require expensive and complex equipment, operates with photographs obtained during the investigation, constructs the whole area of an object in the frame, and allows for synthesizing data from various sources. However, the quality of the resulting models depends on the number of photographs and compliance with the rules of measurement and panning of objects. It is also important that the researcher skilled in the use of software tools to build three-dimensional models from photographic images is able to make adjustments at each stage. Conclutions. The possibility of producing a three-dimensional reconstruction of the crime and solving problems not only within forensic firearm examination, but also those kinds, with which it can be combined, is reflected.

SUGGESTIONS ON AMENDING THE METHODOLOGY OF ESTABLISHING THE OBJECT BELONGING TO FIREAREMS AMMUNITION AND ITS SUITABILITY FOR FIRING

The article considers structural features of certain types of cartridges in relation to firearms, as well as non-combat cartridges, auxiliary cartridges and products that are structurally similar to cartridges, which are submitted for research as part of forensic firearm examination, especially in connection with the ongoing war in Ukraine, occupation of part of its territory and as a result with mass distribution of illegal weapons and ammunition in Ukraine. The article outlines problematic issues of dismantling cartridges in relation to small arms of large caliber, cartridges loaded with special bullets, particular types of silent bullets, non-combat cartridges. The article also highlights issues of optimizing actions of a forensic expert while research, the objects of which are products that are structurally similar to small arms cartridges, but loaded with propellants, pyrotechnic mixtures, poisonous substances, along with products that coincide with small arms cartridges in size and partially in design.
 Backlog of approaches incorporated in the current methodology for researching ammunition is identified in the article and practical need for updates and additions is actualized.
 Proposals were raised to amend the Methodology aimed at increasing safety of forensic firearm examinations, regulating actions of a forensic expert in deciding on dismantling cartridges. It is suggested to use modern devices for reloading cartridges in forensic practice to provide a better and safer research. A procedure for a forensic expert course of action while study of cartridges which are sent for forensic examination in a single copy to minimize the impact on both the object under study and its components, is proposed.

Firearm examination: Examiner judgments and computer-based comparisons.

Forensic firearm examination provides the court of law with information about the source of fired cartridge cases. We assessed the validity of source decisions of a computer‐based method and of 73 firearm examiners who compared breechface and firing pin impressions of 48 comparison sets. We also compared the computer‐based method's comparison scores with the examiners' degree‐of‐support judgments and assessed the validity of the latter. The true‐positive rate (sensitivity) and true‐negative rate (specificity) of the computer‐based method (for the comparison of both the breechface and firing pin impressions) were 94.4% and at least 91.7%, respectively. For the examiners, the true‐positive rate was at least 95.3% and the true‐negative rate was at least 86.2%. The validity of the source decisions improved when the evaluations of breechface and firing pin impressions were combined and for the examiners also when the perceived difficulty of the comparison decreased. The examiners were reluctant to provide source decisions for "difficult" comparisons even though their source decisions were mostly correct. The correlation between the computer‐based method's comparison scores and the examiners' degree‐of‐support judgments was low for the same‐source comparisons to negligible for the different‐source comparisons. Combining the outcomes of computer‐based methods with the judgments of examiners could increase the validity of firearm examinations. The examiners' numerical degree‐of‐support judgments for their source decisions were not well‐calibrated and showed clear signs of overconfidence. We suggest studying the merits of performance feedback to calibrate these judgments.

Development of a Novel Finger-Trigger Interface for Trigger Pull Measurement.

Trigger pull is the force that needs to be exerted on the trigger to discharge a firearm. The measurement of trigger pull can assist in the evaluation of the safety, function, and manufacturing characteristics associated with a firearm during the forensic firearm examination process. Nonetheless, the accuracy and uncertainty of trigger pull measurements may be affected by the measuring device, test procedure, and environmental conditions. In this work, an innovative finger-trigger interface device was developed to facilitate accurate trigger pull measurements. The idea was to reduce the variation related to the position of the measurement device on the trigger in existing measuring methods and devices. Three force sensors based on different technologies were initially evaluated. While two of the three sensors failed to produce data, the miniature capacitive plate sensor exhibited high precision and a linear response over the range of typical trigger pulls. To examine the effects of the finger-trigger interface on trigger pull measurement, different sensor housing prototypes were designed in silico and 3D printed for the construction of three finger-trigger interface devices. The performance of each finger-trigger interface device was evaluated by measuring the trigger pulls of several selected firearms and comparing the data to a previously published study. Our preliminary results demonstrated the novel finger-trigger interface device offered a new way to measure trigger pull in situ with acceptable accuracy and precision.

Advances In Microscopy and Microanalysis In The Field of Forensic Firearm Examination and Identification

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Advances In Microscopy and Microanalysis in the Field of Forensic Firearm Examination and Identification

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.