LEONARD WK5: Firearms, Explosives and Arson
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Leonard Okolienta posted Apr 28, 2024 10:15 PM
1. How are spent casings recovered from a crime scene examined? Do they possess individual or class characteristics?
Spent casings recovered from a crime scene are examined through a forensic process to identify both class and individual characteristics that can link them to a specific firearm.
When firearms are discharged, unique tool marks are transferred to the spent cartridge casings and bullets. These tool marks are produced during the manufacturing process of the firearm and are unique to each weapon. Forensic examiners collect these casings from the crime scene and compare them with test-fired casings from a suspected firearm using comparison microscopes. If the tool marks on the spent casings match those on the test-fired casings, it can be concluded that the casings were discharged from that firearm (National Institute of Justice, n.d.).
A clear case example of a court case between United States v. Davis. In this case, forensic experts testified about the characteristics of spent shell casings found at various crime scenes. They provided opinions that certain bullets and casings found at one crime scene could be associated with bullets, spent shell casings, or firearms recovered from other crime scenes. The case involved serious charges, including racketeering, murder, and various related gun charges (United States v. Davis, 2019). This case shows the importance of forensic tool mark and firearms identification evidence in linking spent casings to specific criminal activities and firearms.
Spent casings recovered from a crime scene are examined through a meticulous process that involves the analysis of both class and individual characteristics. Class characteristics are measurable features of a specimen that indicate a restricted group source, such as the width of the tip of a screwdriver or the width of land and groove impressions on a bullet (National Forensic Science Technology Center, n.d.). These characteristics can show that a casing may be like or consistent with a questioned source but are not unique to that source (National Forensic Science Technology Center, n.d.).
Spent casings from a crime scene possess both individual and class characteristics that are crucial for forensic examinations. Class characteristics are measurable features that indicate a restricted group source, such as the width of land and groove impressions on a bullet, which can be consistent with a questioned source but are not unique to it. Individual characteristics are marks produced by the random imperfections or irregularities on the surfaces of the tools used during the manufacturing process, which can be uniquely identifiable with a source, such as striated and/or impressed marks produced by the action of the firearm on the casing (North Carolina Department of Justice, n.d.).
It is good to note that while individual characteristics can provide a unique match to a specific firearm, class characteristics alone are not sufficient to link a casing to a particular weapon definitively. The combination of both types of evidence, however, can significantly strengthen the case (National Forensic Science Technology Center, n.d.).
2. Describe methods utilized at a crime scene to detect accelerants and explosive material.
At a crime scene, various methods are utilized to detect accelerants and explosive materials. These methods include visual inspection, sample collection and packaging, canine detection, portable detection tools, and laboratory analysis.
Visual Inspection: Visual inspection is one of the primary methods used at a crime scene to detect accelerants and explosive materials. Investigators begin with a visual inspection of the scene, especially the origin of the fire, as it will have the highest probability of containing any ignitable liquid residues (ILRs) left from the use of accelerants (Wikipedia, n.d.). Trained investigators carefully examine the scene, paying close attention to specific areas, especially the origin of the fire.
Determining the Origin: Investigators first identify the point of origin of the fire. This area has the highest likelihood of containing any ignitable liquid residues left from the use of accelerants. Accelerants would be the first materials ignited due to their lower ignition temperature compared to other materials.
Visual Clues: Trained investigators look for visual cues that indicate the use of accelerants:
Intense localized burning: Areas with unusually intense or concentrated burning may suggest accelerant use.
Pour patterns: Detecting patterns where accelerants were poured or splashed can provide evidence.
Significance: Detecting accelerants through visual inspection can be crucial for classifying a fire as accidental or arson.
Positive identification of accelerants holds strong evidentiary value during legal proceedings.
Sample Collection and Packaging: Once potential accelerants are detected, samples are carefully collected and packaged in containers that will not contaminate the evidence (Wikipedia, n.d.).
Preparation: Before evidence is collected, it’s crucial to ensure that the scene is safe and that there are no unexploded devices or hazardous materials present. If such items are found, expert assistance from bomb squads or certified technicians is required (InterFIRE, n.d.).
Photographic Documentation: All potential evidence should be photographed “as found” before any collection takes place. This helps maintain the integrity of the evidence and provides context for later analysis (InterFIRE, n.d.).
Collection Guidelines: Evidence must be collected with clean tools and placed in clean, unused containers to prevent contamination. For accelerants, metal cans are often used because they don’t allow vapors to escape and preserve the sample well (InterFIRE, n.d.).
Packaging: Wet items should be allowed to dry before packaging to prevent degradation. Each piece of evidence should be packaged individually, and tools should be cleaned between collections to avoid cross-contamination (InterFIRE, n.d.).
Labeling and Chain of Custody: Proper labeling and maintaining a chain of custody are essential to ensure that the evidence can be tracked and is admissible in court (InterFIRE, n.d.).
Laboratory Analysis: The collected samples are then analyzed in forensic laboratories using sensitive analytical instruments, such as gas chromatography-mass spectrometry (GC-MS), to identify the chemical composition of the accelerants (Wikipedia, n.d.).
Canine Detection: Specially trained accelerant detection canines are used to sniff out traces of ignitable liquids. These dogs can pinpoint areas for investigators to collect samples (Wikipedia, n.d.). Canine Detection brings a level of accuracy and efficiency to fire scene investigations, allowing for quicker identification of potential accelerants and helping to guide the collection of evidence (Wikipedia, n.d.).
Portable Detection Tools: Photoionization detectors (PIDs) are portable instruments that can detect volatile organic compounds (VOCs) at low levels. PIDs are quick, simple to use, and sensitive to commonly found accelerants. These tools are non-destructive and will not affect the air sample, which can be captured at the same time as the measurement for further lab analysis. They reduce the quantity and cost of lab samples required to conclude the cause of the fire and are deployed rapidly and safely to test areas where residual traces of accelerant may remain, such as between floorboards and under carpets (Ion Science UK, n.d.).
These methods collectively help investigators determine whether a fire or explosion was accidental or intentional and provide crucial evidence in cases of arson. The combination of fieldwork and laboratory analysis is essential for a positive identification of fire accelerants at a crime scene.
References:
InterFIRE. (n.d.). Evidence Collection, Accelerants. Retrieved from interFIRE.
Ion Science UK. (n.d.). Detecting Arson Accelerants for Fire/Arson Investigators. Retrieved from Ion Science UK.
North Carolina Department of Justice. (n.d.). Firearms & Tool Mark. Retrieved from NCDOJ
National Forensic Science Technology Center. (n.d.). Class and Individual Characteristics. Retrieved from NFSTC.
National Institute of Justice. (n.d.). The Science Behind Firearm and Tool Mark Examination. Retrieved from NIJ website.
United States v. Davis, Case No.: 4:18-cr-00011. (2019). Casetext. Retrieved from Casetext.
Wikipedia. (n.d.). Detection of fire accelerants. Retrieved from Wikipedia.
Wikipedia. (n.d.). Fire accelerant. Retrieved from Wikipedia.

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