 | This article includes a list of general references, but it lacks sufficient corresponding inline citations .(December 2016) |
| This article includes a list of general references, but it lacks sufficient corresponding inline citations .(December 2016) |
Gunshot residue (GSR), also known as cartridge discharge residue (CDR), gunfire residue (GFR), or firearm discharge residue (FDR), consists of all of the particles that are expelled from the muzzle of a gun following the discharge of a bullet. It is principally composed of burnt and unburnt particles from the explosive primer, the propellant (gunpowder), stabilisers and other additives. [1] The act of firing a bullet incites a highly pressurised, explosive reaction that is contained within the barrel of the firearm, which expels the bullet. [1] This can cause the bullet, the barrel, or the cartridge to become damaged, meaning gunshot residue may also included metallic particles from the cartridge casing, the bullet jacket, as well as any other dirt or residue contained within the barrel that could have become dislodged.
Law enforcement commonly use swabbing, adhesives and vacuums with very fine filters to collect GSR. [2] They commonly swab the web of the non-firing hand to look for gunshot residue if they are suspected to have discharged a firearm themselves or were in close contact with one at the time discharge. Hair and clothing also accumulate GSR; typically a double-sided adhesive is used to sample areas that may have been exposed to such residue. It is also possible to use a swab moistened with 5% Nitric acid for collection. [2]
To determine if GSR is present in an area, presumptive tests, such as the modified Griess test and the sodium rhodizonate test, are performed. Any presumptive GSR samples are collected for confirmatory testing using instruments such as Scanning electron microscopy dispersive X-ray spectrometry (SEM-EDX) Flame or Graphite Furnace Atomic Absorption Spectrometry. [3] There are both inorganic and organic components in GSR. Organic GSR (OGSR) consists of organic compounds such as nitroglycerine. [2] Organic compounds can originate from the primer, propellants, lubricants or other additives used by manufacturers. [3] Analysis of OGSR is not done with the same instrumentation as stated above, instead techniques like Gas Chromatography-Mass Spectrometry are used. [3]
The detection of nitrates and nitrates for GSR has been around since the early 1900s. The first recorded use of paraffin wax as a lifting medium was done by Dr. Iturrioz in 1914 and was popularized in 1933 by Teodoro Gonzalez of the Mexico City Police Laboratory. [3] The aptly named paraffin test is also referred to as the diphenylamine test, dermal nitrate test and the Gonzalez test. This test consisted of coating a suspect’s hands with paraffin wax, allowing it to solidify and peeling it away before adding a diphenylamine/sulfuric acid reagent. The presence of dark blue spots is said to indicate a positive result. [3] This is no longer used in casework due to the high number of false positives caused by the commonality of nitrates and nitrites in a variety of mundane products such as fertilisers. [2]
In 1971 John Boehm presented some micrographs of gunshot residue particles found during the examination of bullet entrance holes using a scanning electron microscope. If the scanning electron microscope is equipped with an energy-dispersive X-ray spectroscopy detector, the chemical elements present in such particles, mainly lead, antimony and barium, can be identified.
In 1979 Wolten et al. proposed a classification of gunshot residue based on composition, morphology, and size. Four compositions were considered characteristic:
The authors proposed some rules about chemical elements that could also be present in these particles.
Wallace and McQuillan published a new classification of the gunshot residue particles in 1984. They labeled as unique particles those that contain lead, antimony, and barium, or that contain antimony and barium. Wallace and McQuillan also maintained that these particles could contain only some chemical elements.
The most definitive method to determine whether a particle is characteristic of GSR is by its elemental profile. GSR mostly derives from its propellants and primer cap; which includes an explosive, oxidizer, fuel, lubricants, stabilizers and other additives. [4] An approach to the identification of particles characteristic of or consistent with GSR is to compare the elemental profile of the recovered particulate with that collected from case-specific known source items, such as the recovered weapon, Cartridge cases or victim-related items whenever necessary. This approach was called ‘‘case by case’’ by Romolo and Margot in an article published in 2001. In 2010 Dalby et al. published the latest review on the subject and concluded that the adoption of a "case by case" approach to GSR analysis must be seen as preferable, in agreement with Romolo and Margot.
In light of similar particles produced from extraneous sources, both Mosher et al. (1998) aima et al. (2012) presented evidence of pyrotechnic particles that can be mistakenly identified as GSR. Both publications highlight that certain markers of exclusion and reference to the general population of collected particulate can help the expert in designating GSR-similar particles as firework-sourced.
Particle analysis by scanning electron microscope equipped with an energy-dispersive X-ray spectroscopy detector is the most powerful forensic tool that investigators can use to determine a subject's proximity to a discharging firearm or contact with a surface exposed to GSR (firearm, spent cartridge case, target hole). Test accuracy requires procedures that avoid secondary gunshot residue transfer from police officers onto subjects or items to be tested, and that avoid contamination in the laboratory.
The two main groups of specialists currently active on gunshot residue analysis are the Scientific Working Group for Gunshot Residue (SWGGSR) based in USA and the ENFSI EWG Firearms/GSR Working Group based in Europe. [5]
A positive result using SEM-EDX spectroscopy will generate x-ray spectra characteristc of GSR, likely containing combinations of metals such as Pb-Sb-Ba or Sb-Ba. Spectra may also indicate the presence of Ca, S and Si but is not always indicative of GSR. [2] GSR may be present when an individual discharged a firearm or was close by when a discharge occurred. [6] GSR has been observed to undergo both secondary and tertiary transfers, meaning the presence of GSR may be attributed to the persistence of the residue and the unpredictability of human interaction. [5]
A negative result on someone could mean they were near it but not close enough for gunshot residue to land on them, or it can mean that the gunshot residue deposited on them wore off. [lower-alpha 1] Gunshot residue can also be removed from surfaces by washing, wiping, or brushing it off, so a negative result cannot fully rule out a gun was not fired by the tested object or area. [6] Expelled gunshot residue does not travel very far from the muzzle because the particles lack momentum. Depending on the type of fire arm and ammunition used, it will typically travel no farther than 3–5 feet (0.9–1.5 meters) from the muzzle of the gun. [3]
If the ammunition used was specifically tagged in some way by special elements, it is possible to know the cartridge used to produce the gunshot residue. Inference about the source of gunshot residue can be based on the examination of the particles found on a suspect and the population of particles found on the victim, in the firearm or in the cartridge case, as suggested by the ASTM Standard Guide for gunshot residue analysis by scanning electron microscopy/energy dispersive X-ray spectrometry. Advanced analytical techniques such as ion beam analysis (IBA), carried out after scanning electron microscopy, can support further information allowing one to infer about the source of gunshot residue particles. Christopher et al. showed as the grouping behaviour of different makes of ammunition can be determined using multivariate analysis. Bullets can be matched back to a gun using comparative ballistics.
The abbreviation OGSR is often used to distinguish the organic residues found after a discharge. Organic residues can come from propellants like nitrocellulose and trinitrotoluene, plasticisers like triacetin, stabilizers like diphenylamine and possible reaction products of said compounds. [2] The persistence of these residues is quite low compared to inorganic GSR, with very little quantities of carryover (if any). Detection of OGSR becomes difficult a mere hour after the firing. [2] The persistance of OGSR is subject to environmental factors like wind as well as the substrate it clings to. [1] Organic gunshot residue can be analyzed using methods such as micellar electrokinetic capillary electrophoresis (MEKC), [2] high-performance liquid chromatography and gas chromatography-mass spectrometry. [3]
Presumptive testing always precedes before analysis of a questioned sample. Most presumptive tests involve a chemical reaction that results in a colour change that is detectable with the plain eye. It is important to note that thorough documentation of the scene through notes, photographs etc must be done prior to any presumptive or confirmatory testing in order to maintain chain of custody and avoid contamination.
The Griess test and Walker test are two presumptive tests that can be used to determine if a questioned sample contains nitrites. The Walker test is used to determine GSR area on clothing using naphthylamine-sulfanilic acid soaked photograph paper. Red colouration appears when nitrite ions are present. A variant of the Griess test reagent is sulfanilamide and naphthylamine in an acidic medium. [2] The Modified Griess test detects nitrite compounds, which are a by-product of the combustion of gunpowder. Forensic examiners use this test to determine the gun to target distance. This test is performed first because it does not interfere with the later sodium rhodizonate test. [7] The presence of nitrite ions is what triggers the colour change, and therefore we do not consider this test to be indicative of GSR. [4]
The sodium rhodizonate test can detect the presence of lead and barium; it results in a red or purple color when lead is present in the tested area, [7] and a reddish-brown colour when exposed to barium. [2] It is an extremely sensitive, specific, and efficient method as it can obtain information on the origin of particulate debris, and it can be done on surfaces or objects. [8] This test can’t determine the precise distance of gun to target, however, it is often used around holes to determine if it is consistent with the passage of a bullet. [8]
The Harrison and Gilroy method was introduced in 1959. It is a colorimetric test used to verify the presence of antimony, lead and/or barium. The test involves dampening a cloth with 0.1M hydrochloric acid (HCl), swabbing the item being analysed and allowing that to dry before subjecting it to various reagents. [3] The sensitivities of the reagents used makes this test very unreliable and unrealistic for crime scene analysis. [4]
Analytical chemistry studies and uses instruments and methods to separate, identify, and quantify matter. In practice, separation, identification or quantification may constitute the entire analysis or be combined with another method. Separation isolates analytes. Qualitative analysis identifies analytes, while quantitative analysis determines the numerical amount or concentration.
A scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that contain information about the surface topography and composition of the sample. The electron beam is scanned in a raster scan pattern, and the position of the beam is combined with the intensity of the detected signal to produce an image. In the most common SEM mode, secondary electrons emitted by atoms excited by the electron beam are detected using a secondary electron detector. The number of secondary electrons that can be detected, and thus the signal intensity, depends, among other things, on specimen topography. Some SEMs can achieve resolutions better than 1 nanometer.
Inductively coupled plasma mass spectrometry (ICP-MS) is a type of mass spectrometry that uses an inductively coupled plasma to ionize the sample. It atomizes the sample and creates atomic and small polyatomic ions, which are then detected. It is known and used for its ability to detect metals and several non-metals in liquid samples at very low concentrations. It can detect different isotopes of the same element, which makes it a versatile tool in isotopic labeling.
C-4 or Composition C-4 is a common variety of the plastic explosive family known as Composition C, which uses RDX as its explosive agent. C-4 is composed of explosives, plastic binder, plasticizer to make it malleable, and usually a marker or odorizing taggant chemical. C-4 has a texture similar to modelling clay and can be molded into any desired shape. C-4 is relatively insensitive and can be detonated only by the shock wave from a detonator or blasting cap.
A center-fire is a type of metallic cartridge used in firearms, where the primer is located at the center of the base of its casing. Unlike rimfire cartridges, the centerfire primer is typically a separate component seated into a recessed cavity in the case head and is replaceable by reloading the cartridge.
A microprobe is an instrument that applies a stable and well-focused beam of charged particles to a sample.
Trace evidence occurs when objects make contact, and material is transferred. This type of evidence is usually not visible to the naked eye and requires specific tools and techniques to be located and obtained. Due to this, trace evidence is often overlooked, and investigators must be trained to detect it. When it comes to an investigation trace evidence can come in many different forms and is found in a wide variety of cases. This evidence can link a victim to suspects and a victim or suspect to the crime scene.
Ion beam analysis (IBA) is an important family of modern analytical techniques involving the use of MeV ion beams to probe the composition and obtain elemental depth profiles in the near-surface layer of solids. All IBA methods are highly sensitive and allow the detection of elements in the sub-monolayer range. The depth resolution is typically in the range of a few nanometers to a few ten nanometers. Atomic depth resolution can be achieved, but requires special equipment. The analyzed depth ranges from a few ten nanometers to a few ten micrometers. IBA methods are always quantitative with an accuracy of a few percent. Channeling allows to determine the depth profile of damage in single crystals.
Characterization, when used in materials science, refers to the broad and general process by which a material's structure and properties are probed and measured. It is a fundamental process in the field of materials science, without which no scientific understanding of engineering materials could be ascertained. The scope of the term often differs; some definitions limit the term's use to techniques which study the microscopic structure and properties of materials, while others use the term to refer to any materials analysis process including macroscopic techniques such as mechanical testing, thermal analysis and density calculation. The scale of the structures observed in materials characterization ranges from angstroms, such as in the imaging of individual atoms and chemical bonds, up to centimeters, such as in the imaging of coarse grain structures in metals.
A contact shot is a gunshot wound incurred while the muzzle of the firearm is in direct contact with the body at the moment of discharge. Contact shots are often the result of close-range gunfights, suicide, or execution.
A blank-firing adapter or blank-firing attachment (BFA), sometimes called a blank adapter or blank attachment, is a device used in conjunction with blank ammunition for safety reasons, functional reasons or a combination of them both. Blank firing adapters are required for allowing blank ammunition to cycle the bolts of most semi-automatic and automatic firearms. It can also be a safety feature designed to break up the plugs replacing the bullet in military blanks as well as divert the hot gases from a blank discharge out to the sides, reducing the risk of injury to the target of an aimed shot.
Aspex Corporation, founded in 1992, is a supplier of electron microscopy tools to researchers, developers and manufacturers working on Process control through automated scanning electron microscope and energy-dispersive X-ray spectroscopy.
A magnetic lens is a device for the focusing or deflection of moving charged particles, such as electrons or ions, by use of the magnetic Lorentz force. Its strength can often be varied by usage of electromagnets.
QEMSCAN is the name for an integrated automated mineralogy and petrography system providing quantitative analysis of minerals, rocks and man-made materials. QEMSCAN is an abbreviation standing for quantitative evaluation of minerals by scanning electron microscopy, and a registered trademark owned by FEI Company since 2009. Prior to 2009, QEMSCAN was sold by LEO, a company jointly owned by Leica and ZEISS. The integrated system comprises a scanning electron microscope (SEM) with a large specimen chamber, up to four light-element energy-dispersive X-ray spectroscopy (EDS) detectors, and proprietary software controlling automated data acquisition. The offline software package iDiscover provides data processing and reporting functionality.
Micro x-ray fluorescence (µXRF) is an elemental analysis technique that relies on the same principles as x-ray fluorescence (XRF). Synchrotron X-rays may be used to provide elemental imaging with biological samples. The spatial resolution diameter of micro x-ray fluorescence is many orders of magnitude smaller than that of conventional XRF. While a smaller excitation spot can be achieved by restricting x-ray beam using a pinhole aperture, this method blocks much of the x-ray flux which has an adverse effect on the sensitivity of trace elemental analysis. Two types of x-ray optics, polycapillary and doubly curved crystal focusing optics, are able to create small focal spots of just a few micrometers in diameter. By using x-ray optics, the irradiation of the focal spot is much more intense and allows for enhanced trace element analysis and better resolution of small features. Micro x-ray fluorescence using x-ray optics has been used in applications such as forensics, small feature evaluations, elemental mapping, mineralogy, electronics, multi-layered coating analysis, micro-contamination detection, film and plating thickness, biology and environment.
Nuclear forensics is the investigation of nuclear materials to find evidence for the source, the trafficking, and the enrichment of the material. The material can be recovered from various sources including dust from the vicinity of a nuclear facility, or from the radioactive debris following a nuclear explosion.
Forensic firearm examination is the forensic process of examining the characteristics of firearms or bullets left behind at a crime scene. Specialists in this field try to link bullets to weapons and weapons to individuals. They can raise and record obliterated serial numbers in an attempt to find the registered owner of a weapon and look for fingerprints on a weapon and cartridges.
The characterization of nanoparticles is a branch of nanometrology that deals with the characterization, or measurement, of the physical and chemical properties of nanoparticles. Nanoparticles measure less than 100 nanometers in at least one of their external dimensions, and are often engineered for their unique properties. Nanoparticles are unlike conventional chemicals in that their chemical composition and concentration are not sufficient metrics for a complete description, because they vary in other physical properties such as size, shape, surface properties, crystallinity, and dispersion state.
The European Network of Forensic Science Institutes (ENFSI) was founded in 1995 in order to facilitate dialogue among the forensic science practitioners of Europe, as well as improving the quality of forensic science delivery. It has close cooperation with European police forces. In addition to quality, research, and education, different forensic disciplines address domain-relevant issues within expert working groups (EWGs) to the highest degree such that ENFSI is recognized as the monopoly organization for forensics science by the European Commission. ENFSI functions as a non-profit organization.
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