A Validation Study of Bullet and Cartridge Case Comparisons Using Samples Representative of Actual Casework

The foundation of firearm and tool mark identification is that no two tools should produce the same microscopic marks on two separate objects that they would be inaccurately or wrongly identified. Studies addressing the validity of identification infrequently employ tests that mirror realistic casework scenarios. This study attempted to do so using a double‐blind process, reducing test‐taking bias. Test kits including bullets and cartridge cases but not the associated firearms were completed by 31 analysts from 22 agencies. Analysis of the results demonstrated an overall error rate of 0.303%, sensitivity of 85.2%, and specificity of 86.8%. Variability in performance across examiners is addressed, and the effect of examiners’ years of experience on identification accuracy is explored. Finally, the article discusses the importance of studies using realistic case work scenarios when validating the field's performance and in providing courts with usable indicators of the accuracy of firearm and tool mark identification.     

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.     

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.     

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.     

Automated detection of regions of interest in cartridge case images using deep learning

This paper explores a deep-learning approach to evaluate the position of circular delimiters in cartridge case images. These delimiters define two regions of interest (ROI), corresponding to the breech face and the firing pin impressions, and are placed manually or by an image-processing algorithm. This positioning bears a significant impact on the performance of the image-matching algorithms for firearm identification, and an automated evaluation method would be beneficial to any computerized system. Our contribution consists in optimizing and training U-Net segmentation models from digital images of cartridge cases, intending to locate ROIs automatically. For the experiments, we used high-resolution 2D images from 1195 samples of cartridge cases fired by different 9MM firearms. Our results show that the segmentation models, trained on augmented data sets, exhibit a performance of 95.6% IoU (Intersection over Union) and 99.3% DC (Dice Coefficient) with a loss of 0.014 for the breech face images; and a performance of 95.9% IoU and 99.5% DC with a loss of 0.011 for the firing pin images. We observed that the natural shapes of predicted circles reduce the performance of segmentation models compared with perfect circles on ground truth masks suggesting that our method provide a more accurate segmentation of the real ROI shape. In practice, we believe that these results could be useful for firearms identification. In future work, the predictions may be used to evaluate the quality of delimiters on specimens in a database, or they could determine the region of interest on a cartridge case image.     

Transnational organized crime and gun violence. A case for firearm forensic intelligence sharing

A threat to the safety of citizens in any country, the criminal misuse of firearms presents a wider danger to a nation's security, peace, stability and development. Firearms and their related evidence know no borders. It is not uncommon to find the murder weapon from a shooting in one city ending up in another city, country, or continent. No country remains unaffected by firearm violence. This paper describes how transnational organized crime and gun violence are interrelated, and makes the case for the international sharing of firearm forensic intelligence through Interpol's IBIN Program as an integral component of an intelligence-led policing strategy to combat cross-border gun related crime. With such a strategy in place, internationally mobile criminals who use firearms to further their illicit activities can no longer escape detection.     

Three-dimensional surface topography acquisition and analysis for firearm identification

In the last decade, computer-based systems for the comparison of microscopic firearms evidence have been the subject of considerable research work because of their expected capability of supporting the firearms examiner through the automated analysis of large amounts of evidence. The Integrated Ballistics Identification System, which is based on a two-dimensional representation of the specimen surface, has been widely adopted in forensic laboratories worldwide. More recently, some attempts to develop systems based on three-dimensional (3D) representations of the specimen surface have been made, both in the literature and as industrial products, such as BulletTRAX-3D, but fundamental limitations in achieving fully automated identification remain. This work analyzes the advantages and disadvantages of a 3D-based approach by proposing an approach and a prototype system for firearms evidence comparison that is based on the acquisition and analysis of the 3D surface topography of specimens, with particular reference to cartridge cases. The concept of 3D virtual comparison microscope is introduced, whose purpose is not to provide fully automated identification, but to show how the availability of 3D shape information can provide a whole new set of verification means, some of them being described and discussed in this work, specifically, visual enhancement tools and quantitative measurement of shape properties, for supporting, not replacing, the firearm examiner in reaching the final decision.     

Form follows function: Applying photographic content analysis to forensic firearm identification

Drawing forensic conclusions from an image or a video is known as “photographic content analysis.” It involves the analysis of an image, as well as objects, actions, and events depicted in images or video. In recent years, photographic depictions of objects suspected as illegal firearms have substantially increased, appearing on CCTV surveillance footage, captured by mobile phones and shared on social media. However, the law in Israel states that a person can be charged with illegally possessing a firearm only if it can be proven that the object is capable of shooting with lethal bullet energy. This becomes more challenging in cases where the firearm was not physically seized, and the evidence exclusively consists of images and video. In this study, photographic content analysis was applied to images and video where objects suspected as commercial or improvised firearms had been depicted. An image and event sequence reconstruction video databases of both firearms and replicas were created in order to better define firearm-specific functional morphological features. We demonstrate that it is possible to classify an object as a firearm by analyzing the functional, and not only the esthetic, morphology in images and video. It is also shown that event sequence reconstruction in video may be used to infer that an object suspected as a firearm has the capacity to shoot by confirming the occurrence of a shooting act or shooting process. Thus, photographic content analysis may be used to forensically establish that an object depicted in an image or a video is a firearm by ruling out other known scenarios, and without physically seizing it.     

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.     

Swabbing firearms for handler's DNA

Obtaining quality DNA profiles from firearms can be instrumental in assisting criminal investigations. Typically, swabbings of firearms for handler's DNA are conducted on specific regions of the firearm prior to submission to the laboratory for analysis. This review examines and compares 32 cases whose gun swabbings were either analyzed individually according to the specific region which was swabbed, or analyzed collectively by combining the swabbings from all the individual areas. Those firearms whose swabs were analyzed separately exhibited lower DNA yields and consequently fewer loci exhibiting genotypes. Those cases whose swabs were analyzed collectively exhibited higher DNA yields and consequently greater numbers of loci exhibiting genotypes. These findings demonstrate that collective swabbings result in more complete profiles and lead to the recommendation that a firearm be swabbed in its entirety using no more than two swabs.     

Major vascular neck injury from a handgun cartridge casing

We present a case from the Johannesburg General Hospital of a zone II low-velocity penetrating neck injury with involvement of the ipsilateral subclavian artery. When the "bullet" was retrieved, it was noted not to be an actual bullet but rather a cartridge casing. We speculate that this injury represents one of several possible misfiring scenarios from a homemade firearm. Injuries from homemade firearms are infrequent in the literature, and only one other similar case of a cartridge casing causing a penetrating injury was found. A brief review of homemade handheld firearms is offered.     

Application of lead isotope analysis in shooting incident investigations

A study was conducted to examine the potential of the considerable variability of the lead isotope compositions in bullets (projectiles) and primers in shooting incident investigations. Multiple-collector inductively coupled plasma mass spectrometry (MC-ICP/MS) was used to analyze lead isotopic compositions in projectiles, cartridge cases, firearms discharge residues (FDR) in barrels of firearms and in the gunshot entries. .22 caliber plain lead and plated ammunition and 9 mm Luger full metal jacket (FMJ) ammunition were employed in shooting experiments using semiautomatic pistols. Cotton cloth served as the target material and two firing distances were tested; 1 cm (near contact) and 2 m distances. It was observed that various mechanical or chemical means of cleaning do not completely remove lead deposits ("lead memory") from barrels of firearms. Nonetheless, it was shown that analysis of lead isotopic composition may provide valuable evidence in investigating specific scenarios of shooting incidents. For instance in a shoot-out where several firearms and ammunition brands are involved, it may be feasible to point out which ammunition and/or firearm caused a particular gunshot entry if the ammunition brands involved (bullets and primers) differ considerably in their lead isotopic composition.     

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.     

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.     

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).     

Development of STR profiles from firearms and fired cartridge cases

Fired cartridge cases are a common type of evidence found at crime scenes. However, due to the high chamber temperatures and touch nature of this evidence, DNA testing is not commonly sought because it is believed DNA is only present in low levels, whether it is due to initial low levels of DNA and/or DNA degradation from the heat or inhibition of the PCR reaction. Moreover, very few laboratories report STR typing success with fired cases. This study focused on obtaining STR profiles from fired cartridge cases using the AmpFℓSTR^® MiniFiler™ kit, which is designed to amplify DNA from low level, inhibited, and degraded samples. Comparisons to other STR amplification kits were also conducted. In attempt to simulate casework, random individuals loaded cartridges into a firearm. DNA was recovered from the fired cartridge cases using the double swab technique and extracted using an automated large volume DNA IQ™ method. Initially, testing focused on known shedders handling cartridges for 30 s prior to firing. A significantly greater number of alleles was obtained following amplification with the MiniFiler™ kit versus the PowerPlex^® 16 BIO kit. No alleles were observed using the Identifiler^® kit. In an attempt to better simulate casework, a random selection of laboratory personnel handled shotshells for as long as needed to load and fire the weapon. In this mock sample study, the MiniFiler™ kit successfully amplified an average of 22% of expected alleles from DNA recovered from shotshell cases versus the PowerPlex^® 16 BIO kit where an average of 7% of alleles were observed. However, the total number of alleles obtained from the two kits was not significantly different. The quality of the DNA obtained from fired cases was studied with evidence of inhibition in at least 11% of shotshell case samples. After swabbing the head and the hull of three shotshell cases separately, a significantly greater number of alleles was obtained from the hull as opposed to the head of the fired shotshell case. In addition, after firing, various internal firearm surfaces were swabbed, including the chamber of barrel, ejection port, and breechface, in an attempt to obtain amplifiable DNA. DNA was obtained from the chamber of the barrel and was amplifiable using the MiniFiler™ kit, although mixtures were obtained with extensive drop-in and drop-out making this analysis unlikely to aid an investigation.     

Preliminary evaluation of the persistence of organic gunshot residue

The organic components of gunshot residue (OGSR, also called firearms discharge residue (FDR) or cartridge discharge residue (CDR)) have been studied and discussed in the literature. These residues, consisting of particulates such as burned and unburned powder as well as molecular compounds, are rarely used in casework except for purposes such as shooting reconstructions. Molecular compounds that survive the firing event or that are created as a result of the firing event could, with focused research and development, open a new avenue for forensic gunshot residue analysis. In this study, the persistence of organic gunshot residue was evaluated using diphenylamine (DPA) as a target analyte and ion mobility spectrometry (IMS) as the detection system. Samples were collected from hands using a solvent swabbing technique and the swab was analyzed using direct thermal desorption for sample introduction into the IMS. OGSR was found to persist for at least 4h. Although DPA is a widely used industrial compound, analysis of numerous blank and background samples (n～100) did not show any significant response for DPA using this detector. Variations were noted among individuals and as such, the data set does not support estimation of a half-life as has been done for traditional primer residues. No secondary transfers were observed, suggesting the possibility of skin adhesion via interactions between the lipophilic organic compounds and skin lipids. IMS proved valuable as a means of generating patterns for forensic pattern matching and shows promise as a screening tool applied to firearms discharge.     

Estimating the time since discharge of spent cartridges: A logical approach for interpreting the evidence

Estimating the time since discharge of a spent cartridge or a firearm can be useful in criminal situations involving firearms. The analysis of volatile gunshot residue remaining after shooting using solid-phase microextraction (SPME) followed by gas chromatography (GC) was proposed to meet this objective. However, current interpretative models suffer from several conceptual drawbacks which render them inadequate to assess the evidential value of a given measurement. This paper aims to fill this gap by proposing a logical approach based on the assessment of likelihood ratios. A probabilistic model was thus developed and applied to a hypothetical scenario where alternative hypotheses about the discharge time of a spent cartridge found on a crime scene were forwarded. In order to estimate the parameters required to implement this solution, a non-linear regression model was proposed and applied to real published data. The proposed approach proved to be a valuable method for interpreting aging-related data.     

An Investigation into Whether or Not the Class and Individual Characteristics of Five Turkish Manufactured Pistols Change During Extensive Firing

Abstract:  In order to assess whether or not the class and individual characteristics of a firearm change over time, five different makes of Turkish self-loading pistol were tested and were each fired a large number of times. The class and individual characteristics were identified for each pistol and the first fired cartridge case was compared with the subsequent consecutive 250th fired cases for each pistol. It was found that there were slight changes in some of the individual and class characteristics; however, this was not statistically significant and did not affect the ability of the firearms examiner to match the first fired case to the last fired case for each firearm tested.     

The criminal use of improvised and re-activated firearms in Great Britain and Northern Ireland.

Following the Hungerford Massacre the British Government imposed additional strict firearms legislation in 1988 that involved several classes of arms being placed into the prohibited category. By way of compensation a scheme was introduced to allow the unrestricted possession and transfer of the newly prohibited arms, other firearms and "prohibited weapons", if de-activated to a standard acceptable to the Secretary of State. Approved standards for firearm de-activation were drawn up in 1989. The inspection of the de-activated arms was devolved to the two Gun Barrel Proof Houses at London and Birmingham, as otherwise the task of inspecting the thousands of guns involved would have overloaded the firearms section at the Huntingdon Forensic Science Service Laboratory, who were already dealing with criminal firearms cases submitted by 41 of the 43 police forces throughout England and Wales, as well as providing technical assistance to the Home Office and Government Ministers. Members of the Gun Trade made representations to the Minister involved during the initial stages of setting up the official de-activation standards. This resulted in some measure of compromise in the range and nature of the de-activation requirements. Although it was clear that some individuals possessing the necessary skill and equipment might attempt to restore the odd weapon to a working condition, the scheme appeared to work reasonably well for the next few years. However, over the passage of time, criminal casework submissions to the Huntingdon Laboratory from industrial city areas along the M62 corridor of northern England revealed a steadily growing trend in the use of re-activated arms, which in a significant number of cases involved the use of fully automatic weapons. At first, the nature of the re-activation processes used to restore these arms was quite crude. However, with the passage of time a steady improvement in the machining and welding skills used by the some of the culprits involved became more and more apparent, as was a move by them to bulk restoration. The use of restored arms in serious and often drug related crime, spread to the other mainland British cities, and eventually to Northern Ireland. More rigorous de-activation standards were introduced in 1995 to help counter this perceived threat, particularly in respect of handguns and full-automatic weapons. Blank cartridge pistols and air cartridge pistols were also being modified to allow their use with bulleted ammunition in the commission of criminal offences. As a result all air cartridge guns were placed into the prohibited weapons category in 2003, and the possession of imitation firearms in a public place without good reason, also became an offence. The Government is now considering further legislation, which will affect the sale of replica firearms and cartridge reloading equipment and materials.