Advancing Forensic Analysis of Gunshot Acoustics

2016

In order to study gunshot sounds, experimental shootings were conducted in an open shooting range to record the sound of gunshots. The results were tabulated for a total of 168 gunshots. Shots were fired using pistols, revolvers, submachine guns, rifl es and shotguns in di fferent calibres from selected distances relative to the recording devices. Both a conventional sound level meter (SLM) and a measurement microphone were used. These were placed at selected points behind the shooting position and the sound of each shot was recorded. At the same time, the signal received by the microphone was transferred to a computer connected through an appropriate audio interface with a pre-amplifier. The peak amplitude of the gunshot was calculated in the accepted engineering units (dB) of sound pressure level. The shortest distance for the recordings was 9.60 m and the furthest was 38.40 m. The experiment was carried out using the following calibres: 6.35 mm, 7.62 mm Tokarev, 7.65 mm, 9 mm Sho...

2016

Acoustic gunshot signals consist of a high amplitude and short duration impulsive sound known as the muzzle blast and the shock wave. This experiment involved documenting gunshot muzzle blast sounds produced by eight commonly used firearms including Remington 870, Colt 45, Glock 19 with 9mm ammunition, Glock 23, Sig 239, AR15, 22LR, and Ruger SP 101 with 357 magnum and 38 special ammunition. An elevated microphone bracket (3m above the ground) was built to achieve a quasianechoic environment for the duration of the muzzle blast. Twelve microphones (GRAS 40DP) were mounted on the bracket in a semi-circular arc to observe the azimuthal variation of the muzzle blast. Signals were recorded using LabVIEW. Similarities and differences among waveforms are presented.

Particularly, I would like to thank Prof. Rafik Goubran for his support, guidance and enlightenment through all these years and Dr. David Lo for being a wonderful colleague, supervisor and friend. Without him, the thesis would not have been possible. My thanks also go to Master Corporal Alex Saumure; recording the data was simple with him taking charge of all the logistics and his ensuring that we had all the equipment. Finally, I would like to thank my love, Chantal Boutin. I am so lucky to have you by my side.

Sound Vibration, 2009

Recreational use of firearms in the United States is commonplace. It is estimated that approximately one-third of households in the U.S. own firearms. 1 There are 28 million Americans who consider themselves hunters, and 13 million went hunting in 2000. 2 Participation in shooting sports without the use of properly worn hearing protection exposes participants to high levels of impulsive noise that may cause hearing loss or tinnitus (ringing in the ear). Firearms may cause permanent hearing loss even after a single or a few unprotected exposures. The present study was initiated to gain a better understanding of the noise exposure created by contemporary firearms using state-of-the-art instrumentation and to ultimately increase our knowledge and awareness of this unique noise hazard.

ArXiv, 2021

The muzzle blast caused by the discharge of a firearm generates a loud, impulsive sound that propagates away from the shooter in all directions. The location of the source can be computed from time-of-arrival measurements of the muzzle blast on multiple acoustic sensors at known locations, a technique known as multilateration. The multilateration problem is considerably simplified by assuming straight-line propagation in a homogeneous medium, a model for which there are multiple published solutions. Live-fire tests of the ShotSpotter gunshot location system in Pittsburgh, PA were analyzed off-line under several algorithms and geometric constraints to evaluate the accuracy of acoustic multilateration in a forensic context. Best results were obtained using the algorithm due to Mathias, Leonari and Galati under a two-dimensional geometric constraint. Multilateration on random subsets of the participating sensor array show that 96% of shots can be located to an accuracy of 15 m or bette...

Sensors

Gun violence has been on the rise in recent years. To help curb the downward spiral of this negative influence in communities, machine learning strategies on gunshot detection can be developed and deployed. After outlining the procedure by which a typical type of gunshot-like sounds were measured, this paper focuses on the analysis of feature importance pertaining to gunshot and gunshot-like sounds. The random forest mean decrease in impurity and the SHapley Additive exPlanations feature importance analysis were employed for this task. From the feature importance analysis, feature reduction was then carried out. Via the Mel-frequency cepstral coefficients feature extraction process on 1-sec audio clips, these extracted features were then reduced to a more manageable quantity using the above-mentioned feature reduction processes. These reduced features were sent to a random forest classifier. The SHapley Additive exPlanations feature importance output was compared to that of the mean...

WIREs Forensic Science

Gunshot residues (GSR) are routinely exploited by forensic scientists in the investigation of firearm-related events. While many new techniques are daily reported in the literature for the analysis of GSR, there is still a significant lack of data on the transfer, persistence, and prevalence of GSR. Such fundamental knowledge is essential to fully exploit the information potential of GSR for investigation or in Court. This article provides an overview of the relevant questions related to GSR, more particularly to infer about the trace's origin (i.e., is it from a firearm discharge?) and the activity that caused transfer (e.g., primary, secondary, or subsequent transfer). GSR production and composition will be briefly described, considering both inorganic and organic components. Then, the available knowledge about the primary transfer, the secondary transfer, and the persistence of GSR will be outlined, as well as the prevalence (background level) of the targeted elements and/or compounds in the environment, more particularly on the hands of people unrelated to firearm incidents. Finally, the methods developed for the collection, analysis, and interpretation of GSR will be discussed. A holistic approach combining fundamental forensic science knowledge about GSR transfer, persistence, and prevalence together with other available information is discussed as a path forward to increase the relevance and value of the GSR trace in practice.

Lancet, 2011

R e s e a r c h i n P r o g r e s s S e m i n a r S e r i e s

Forensic Science International

Gunshot residues (GSR) are a potential form of forensic traces in firearm-related events. In most forensic laboratories, GSR analyses focus on the detection and characterisation of the inorganic components (IGSR), which are mainly particles containing mixtures of lead, barium and antimony originating from the primer. The increasing prevalence of heavy metal-free ammunition challenges the current protocols used for IGSR analysis. To provide complementary information to IGSR particles, the current study concentrated on the organic components (OGSR) arising from the combustion of the propellant. The study focused on four