Forensic Science Lab- Firearm

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Criminalistics: An Introduction to Forensic Science Chapter 9 Firearms, Tool Marks, and Other Impressions Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Firearms • Firearms identification is a discipline mainly concerned with determining whether a bullet or cartridge was fired by a particular weapon. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Handguns (1 of 2) • Single-shot pistols – Fire only one round at a time • Revolvers – Feature several firing chambers within a revolving cylinder – Swing-out revolvers – Break-top revolvers – Solid frame revolvers Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Handguns (2 of 2) • Semi-automatic pistols – Feature a removable magazine – Fire one shot per trigger pull Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Figure 9–1: A Swing-Out Revolver Features a Cylinder That Swings out to the Side of the Weapon to Be Loaded Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Figure 9–2: A Semiautomatic Pistol Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Long Guns (1 of 2) • Long guns may be single-shot, repeating, semiautomatic, or automatic. – Shotguns ▪ Shotgun ammunition (shell) contains numerous ball-shaped projectiles called slug ▪ Narrowing of the smooth barrel (the choke of the shotgun) can concentrate shot when fired Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Long Guns (2 of 2) – Rifles ▪ Feature a barrel with lands and grooves ▪ Bullet ammunition is impressed with lands and grooves during firing Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Figure 9–3: A Bolt-Action Long Gun Uses the Movement of a Bolt Mechanism to Expel the Spent Cartridge Case, Load the Next Round, and Cock the Hammer Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Figure 9–4: A Semiautomatic Long Gun Uses the Energy from the Firing Reaction to Expel the Spent Cartridge Case, Load the Next Round, and Cock the Hammer Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Gun Barrel Markings (1 of 5) • The inner surface of the barrel of a gun leaves its markings on a bullet passing through it. • These markings are unique to each gun. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Gun Barrel Markings (2 of 5) • The gun barrel is produced from a solid bar of steel that has been hollowed out by drilling. • The microscopic drill marks left on the barrel’s inner surface are randomly irregular and serve to impart a uniqueness to each barrel. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Gun Barrel Markings (3 of 5) • The manufacture of a barrel also requires impressing its inner surface with spiral grooves, a step known as rifling. • Rifling is usually accomplished by: – Cutting all grooves in one pass with a cutter known as a broach, or – Pressing all the grooves at once onto the barrel with a tool known as a button, or – Hummer forging the barrel using a mandrel containing the reverse image of the rifling. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Gun Barrel Markings (4 of 5) • The surfaces of the original bore remaining between the grooves are called lands. • The grooves serve to guide a fired bullet through the barrel, imparting a rapid spin to ensure accuracy. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Gun Barrel Markings (5 of 5) • The diameter of the gun barrel, measured between opposite lands, is known as caliber. • Once a manufacturer chooses a rifling process, the class characteristics of the weapon’s barrel will remain consistent. – Each will have the same number of lands and grooves, with the same approximate width and direction of twist. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Figure 9–5: Interior View of a Gun Barrel, Showing the Presence of Lands and Grooves Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Striations • Striations are fine lines found in the interior of the barrel. – These striations form the individual characteristics of the barrel. • It is the inner surface of the barrel of a gun that leaves its striation markings on a bullet passing through it. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Figure 9–9: A Bullet is Impressed with the Rifling Markings of the Barrel When It Emerges from the Weapon Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Figure 9–11: Photomicrograph of Two Bullets through a Comparison Microscope. The Test Bullet is on the Right; the Questioned Bullet is on the Left Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Bullet Examination (1 of 2) • No two rifled barrels will have identical striation markings. • The number of lands and grooves and their direction of twist are obvious points of comparison during the initial stages of an examination between an evidence bullet and a test-fired bullet. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Figure 9–10: A Bullet Holder Beneath the Objective Lens of a Comparison Microscope Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Bullet Examination (2 of 2) • Any differences in these class characteristics immediately serve to eliminate the possibility that both bullets traveled through the same barrel. • Individualization, a goal of in all areas of criminalistics, frequently becomes an attainable reality in firearm examination by examining the striations on a bullet. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Shotguns • Unlike rifled firearms, a shotgun has a smooth barrel. • Shotguns generally fire small lead balls or pellets that are not impressed with any characteristic markings that can be related back to the weapon. • The diameter of the shotgun barrel is expressed by the term gauge. • The higher the gauge number, the smaller the barrel’s diameter. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Firing a Weapon (1 of 2) • Pulling the trigger releases the weapon’s firing pin, causing it to strike the primer, which in turn ignites the powder. • The expanding gases generated by the burning gunpowder propel the bullet forward through the barrel, simultaneously pushing the spent cartridge case or shell back with equal force against the breechface. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Firing a Weapon (2 of 2) • The shell is impressed with markings by its contact with the metal surfaces of the weapon’s firing and loading mechanisms. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Cartridge Case Comparison • The firing pin, breechface, and ejector and extractor mechanism also offer a highly distinctive signature for individualization of cartridge cases. • The shape of the firing pin will be impressed into the relatively soft metal of the primer on the cartridge case. • The cartridge case, in its rearward thrust, is impressed with the surface markings of the breechface. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Computer Imaging (1 of 2) • Computerized imaging technology makes it possible to store bullet and cartridge surface characteristics in a manner analogous to automated fingerprint files. • The National Integrated Ballistics Information Network (NI BIN) produces database files from bullets and cartridge casings retrieved from crime scenes or test fires from retrieved firearms, often linking a specific weapon to multiple crimes. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Computer Imaging (2 of 2) • The ultimate decision for making a final comparison will be determined by the forensic examiner through traditional microscopic methods. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Distance Determination (1 of 3) • When a firearm is discharged, unburned and partially burned particles of gunpowder, in addition to smoke, are propelled out of the barrel along with the bullet toward the target. • If the muzzle of the weapon is sufficiently close, these products will be deposited onto the target. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Distance Determination (2 of 3) • The distribution of gunpowder particles and other discharge residues around a bullet hole permits an assessment of the distance from which a handgun or rifle was fired. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Distance Determination (3 of 3) • The precise distance from which a handgun or rifle has been fired is determined by carefully comparing the powder-residue pattern located on the victim’s clothing or skin against test patterns made when the suspect weapon is fired at varying distances from a target. • By comparing the test and evidence patterns, the examiner may find enough similarity in shape and density upon which to base an opinion as to the distance from which the shot was fired. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Distance Determination without a Suspect Weapon (1 of 2) • In cases where the weapon is held in contact with or less than 1 inch from the target, a star-shaped (stellate) tear pattern around the bullet hole entrance, surrounded by a rim of a smokeless deposit of vaporous lead is usually present. • A halo of vaporous lead (smoke) deposited around a bullet hole is normally indicative of a discharge of 12 to 18 inches or less. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Distance Determination without a Suspect Weapon (2 of 2) • The presence of scattered specks of unburned and partially burned powder grains without any accompanying soot is often observed at distances up to 25 inches (and occasionally as far as 36 inches). • A weapon fired more than 3 feet from a surface/individual will usually not deposit any powder residues, and the only visual indication is a dark ring around the hole, known as a bullet wipe. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Figure 9–16a: Test Powder Patterns Made with a .38 Special Smith & Wesson Revolver Fired at the Following Distances from the Target: Contact Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Figure 9–16b: Test Powder Patterns Made with a .38 Special Smith & Wesson Revolver Fired at the Following Distances from the Target: 6 Inches Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Figure 9–16c: Test Powder Patterns Made with a .38 Special Smith & Wesson Revolver Fired at the Following Distances from the Target: 12 Inches Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Figure 9–16d: Test Powder Patterns Made with a .38 Special Smith & Wesson Revolver Fired at the Following Distances from the Target: 18 Inches Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Figure 9–17: A Contact Shot Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Figure 9–18: (a) A Shirt Bearing a Powder Stain, Photographed under Normal Light. (b) an Infrared Photograph of the Same Shirt Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Gunpowder Residue (1 of 2) • Distance determination involving shotguns must again be related to the suspect weapon and ammunition. • In the absence of a weapon, muzzle-to-target distance can be estimated by measuring the spread of the discharged shot. – As the shot distance increases, the pellets progressively separate and spread out. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Gunpowder Residue (2 of 2) • When garments or other evidence relevant to a shooting are received in the crime laboratory, the surfaces of all items are first examined microscopically for the presence of gunpowder residue. • Chemical tests, such as the Greiss test, may be needed to detect gunpowder residues that are not visible. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Primer Residue on Hands (1 of 2) • Firing a weapon propels residues toward the target, and blows gunpowder and primer residues back toward the shooter. • As a result, traces of these residues are often deposited on the firing hand of the shooter, and their detection can provide valuable information as to whether or not an individual has recently fired a weapon. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Primer Residue on Hands (2 of 2) • Examiners measure the amount of barium and antimony on the relevant portion of the suspect’s hands, such as the thumb web, the back of the hand, and the palm. • Scientists may also characterize the morphology of particles containing these elements to determine whether or not a person has fired, handled a weapon, or was near a discharged firearm. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Figure 9–20a: Adhesive Stubs Used to Sample a Suspect’s Shooter’s Hands Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Figure 9–20b: Sampling a Suspect’s Hand for Gunshot Residue with an Adhesive Stub Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Serial Numbers • Increasingly, the criminalist is requested to restore a serial number when it has been removed or obliterated by grinding, rifling, or punching. • Restoring serial numbers is possible through chemical etching because the metal crystals in the stamped zone are placed under a permanent strain that extends a short distance beneath the original numbers. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Firearm Evidence Collection (1 of 3) • Firearms are collected by holding the weapon by the edge of the trigger guard or by the checkered portions of the grip. • Before being sent to the laboratory, all precautions must be taken to prevent accidental discharge of a loaded weapon. • In most cases, it will be necessary to unload the weapon. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Firearm Evidence Collection (2 of 3) • When a revolver is recovered, the chambers, their positions, and corresponding cartridges must be recorded. • Firearm evidence must be marked for identification (usually a tag on the trigger guard) and a chain of custody must be established. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Firearm Evidence Collection (3 of 3) • Bullets, cartridge cases, and shotgun shells recovered at the crime scene must be packaged in a properly labeled evidence container. • Take care to avoid obliterating striation markings that may be present on the bullet. • Protect the bullet by wrapping it in tissue paper before placing it in a pillbox or an envelope for shipment to the crime laboratory. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Tool Marks (1 of 3) • A tool mark is any impression, cut, gouge, or abrasion caused by a tool coming into contact with another object. – Examining the impression can reveal important class characteristics, such as the size and shape of the tool. – But it is the presence of any minute imperfections on a tool that imparts individuality to that tool. – The shape and pattern of such imperfections are further modified by damage and wear during the tool’s life. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Figure 9-24: A Comparison of a Tool Mark with a Suspect Screwdriver Note how the presence of nicks and breaks on the tool’s edge helps individualize the tool to the mark. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Tool Marks (2 of 3) • The comparison microscope is used to compare crimescene tool marks with test impressions made with the suspect tool. • When practical, the entire object or the part of the object bearing the tool mark should be submitted to the crime laboratory for examination. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Tool Marks (3 of 3) • Under no circumstances must the crime scene investigator attempt to fit the suspect tool into the tool mark. – Any contact between the tool and the marked surface may alter the mark and will, at the least, raise serious questions about the integrity of the evidence. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Other Impressions (1 of 3) • Impressions of other kinds, such as shoe, tire, or fabric impressions, may be important evidence. • Before any impression is moved or otherwise handled, it must be photographed (including a scale) to show all the observable details of the impression. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Other Impressions (2 of 3) • If the impression is on a readily recoverable item, such as glass, paper, or floor tile, transport the evidence to the laboratory intact. • If the surface cannot be submitted to the laboratory, the investigator may be able to preserve the print in a manner similar to lifting a fingerprint. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Other Impressions (3 of 3) • When shoe and tire marks are present at a crime scene, their preservation is best accomplished by photography and casting. • In areas where a bloody footwear impression is very faint or where the subject has tracked through blood leaving a trail of bloody impressions, chemical enhancement can visualize latent or nearly invisible blood impressions. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Points of Comparison (1 of 2) • A sufficient number of points of comparison or the uniqueness of such points will support a finding that both the questioned and test impressions originated from one and only one source. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Points of Comparison (2 of 2) • Computer software and websites may be able to assist in making shoe print and tire impression comparisons. • Also, bite mark impressions on skin and foodstuffs have proven to be important evidence in a number of homicide and rape cases. Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved Copyright Criminalistics, 13e Saferstein/Roy Copyright © 2021, 2018, 2015, 2011 Pearson Education, Inc. All Rights Reserved FIREARMS After an attempted home robbery, you are called to the crime scene. You must interpret the events of the crime. You notice a security camera that has been disabled by gunfire. In addition to the damaged security camera, you find a bullet hole in the wall under the camera. In this experiment, you will analyze bullet trajectory to determine the approximate shoulder height of the suspect. Equipment: Ruler Procedure: 1. Use a ruler to measure the major and minor axis of the bullet hole below (page 3). Measure to the nearest millimeter. 2. Use the equation sin ϴ = 𝑚𝑖𝑛𝑜𝑟 𝑎𝑐𝑖𝑠 (𝑚𝑚) 𝑚𝑎𝑗𝑜𝑟 𝑎𝑥𝑖𝑠 (𝑚𝑚) to determine the angle at which the bullet impacted the wall. Record the angle in Table 1. 3. You find that the bullet hole is located 80" from the floor. 4. As the investigation proceeds, a latent shoe print is recovered 45" from the wall with the bullet hole facing the wall. Draw a diagram of the wall, floor, and bullet trajectory. 5. Use trigonometry to calculate the approximate shoulder height of the shooter. Record the approximate shoulder height in Table 1. If you are unsure how to do this, watch the instructional video. Table 1: Bullet Trajectory Data Post-Lab Questions 1. Record your calculations from Step 2 here. 2. Draw the diagram from Step 4 here. 3. Record your calculations from Step 5 here. 4. What are the winding grooves which help a bullet maintain a stable trajectory called? 5. Would you expect to find more gunshot residue around an entrance or exit hole? Explain your reasoning. 6. Would a hand gun or shot gun be more difficult to trace and determine class characteristics? Explain your answer. 7. The victim has a bullet hole that has a halo of soot surrounding the entrance hole along with scattered specks of powder grains. What do you estimate the distance from the shooter to the victim to be?
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FIREARMS

After an attempted home robbery, you are called to the crime scene. You must
interpret the events of the crime. You notice a security camera that has been
disabled by gunfire. In addition to the damaged security camera, you find a bullet
hole in the wall under the camera. In this experiment, you will analyze bullet
trajectory to determine the approximate shoulder height of the suspect.

Equipment:
Ruler

Procedure:
1. Use a ruler to measure the major and minor axis of the bullet hole below (page
3). Measure to the nearest millimeter.
𝑚𝑖𝑛𝑜𝑟 𝑎𝑐𝑖𝑠 (𝑚𝑚)

2. Use the e...

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