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Forensic Bio Ch. 9
Firearms, Tool Marks, and Other Impressions
| Question | Answer |
|---|---|
| a discipline mainly concerned with determining whether a bullet or cartridge was fired by a particular weapon | firearms examination |
| the study of projectile motion | ballistics |
| cut or low-lying portions between the lands in a rifled bore | grooves |
| the spiral grooves formed in the bore of a firearm barrel that impart spin to the projectile when its fired | rifling |
| interior of firearm barrel | bore |
| raised portion between the grooves in a rifled bore | lands |
| diameter of the bore of a rifled firearm; usually expressed in hundredths of an inch and millimeters | caliber |
| size designation of a shotgun; originally lead balls w/ same diameter as the barrel that would make a pound | gauge |
| rear part of firearm barrel | breechface |
| mechanism in a firearm by which a cartridge of a fired case is withdrawn from the chamber | extractor |
| mechanism in a firearm that throws the fired cartridge case from the firearm | ejector |
| process of determining the distance between the firearm and the target, usually based on the distribution of powder patterns or the spread of a shot pattern | distance determination |
| an interior constriction placed at or near the muzzle end of a shotgun's barrel to control shot dispersion | choke |
| a chemical test used to develop patterns of gunpowder residues around bullet holes | Greiss Test |
| types of handguns | single-shot pistols, revolvers, semi-automatic pistols |
| handgun that can only fire one round at a time | single-shot pistols |
| handgun that feature several firing chambers within a revolving cylinder | revolvers |
| handgun that features a removable magazine and fire one shot per trigger pull | semi-automatic pistols |
| types of long guns | shotguns and rifles |
| long guns may be _______, ____________, ____________, or__________ | single-shot, repeating, semi-automatic, automatic |
| long gun in which the ammunition contains numerous slugs and narrowing of the smooth barrel can concentrate shot when fired | shotgun |
| long gun that features a barrel with lands and grooves and that has bullet ammunition that is impressed with those lands and grooves during firing | rifle |
| ball-shaped projectiles | slugs |
| The number of lands and grooves is a _______ characteristic of a barrel. | class |
| The ___________ characteristics of a rifled barrel are formed by striations impressed into the barrel’s surface. | individual |
| The most important instrument for comparing bullets is the ___________. | comparison microscope |
| To make a match between a test bullet and a recovered bullet, the lands and grooves of the test and evidence bullet must have identical widths, and the longitudinal ___________ on each must coincide. | striations |
| A shotgun has a(n) ___________ barrel. | smooth |
| The diameter of a shotgun barrel is expressed by the term ___________. | guage |
| True or False: A cartridge case can be individualized to a single weapon. ___________ | True |
| The automated firearms search system developed by the FBI and ATF as a unified system incorporating both DRUGFIRE and IBIS technologies available in prior years is known as ___________. | National Integrated Ballistics Information Network (NIBIN) |
| True or False: The distribution of gunpowder particles and other discharge residues around a bullet hole permits an approximate determination of the distance from which the gun was fired. | True |
| A halo of vaporous lead (smoke) deposited around a bullet hole normally indicates a discharge ___________ to ___________ inches from the target. | 12 to 18 |
| If a firearm has been fired more than 3 feet from a target, usually no residue is deposited but a dark ring, known as ___________, is observed. | bullet wipe |
| As a rule of thumb, the spread in the pattern made by a 12-gauge shotgun increases 1 inch for every ___________ of distance from the target. | yard |
| A(n) ___________ photograph may help visualize gunpowder deposits around a target. | infrared |
| True or False: One test method for locating powder residues involves transferring particles embedded on the target surface to chemically treated photographic paper. ___________ | true |
| Determining whether an individual has fired a weapon is done by measuring the elements ___________ and ___________ present on the hands. | barium and antimony |
| Microscopic primer and gunpowder particles on the adhesives applied to a suspected shooter’s hand can be found with a(n) ___________. | Scanning Electron Microscope (SEM) |
| how is restoration of serial numbers possible | because in the stamped zone the metal is placed under a permanent strain that extends beneath the original numbers |
| The clothing of the victim of a shooting must be handled so as to prevent disruption of ___________ around bullet holes. | powder residues |
| A(n) ___________is any impression caused by a tool coming into contact with another object. | tool mark |
| Tool marks compare only when a sufficient number of ___________ match between the evidence and test markings. | striations |
| An imprint may be lifted using lifting sheets or a(n) ___________. | electrostatic lifting device |
| Shoe and tire marks impressed into soft earth at a crime scene are best preserved by ___________ and ___________. | photography and casting |
| A wear pattern, cut, gouge, or other damage pattern can impart ___________ characteristics to a shoe. | individual |
| List three class characteristics of a gun barrel. | number of lands and grooves, width of lands and grooves, and direction of twist |
| Describe how a firearms examiner compares two bullets. | A firearms examiner compares two bullets by checking class characteristics (lands, grooves, and twist) for similarity. They then test-fire a suspect weapon, use a comparison microscope to examine striations, and make a final judgment based on experience. |
| What characteristic does an examiner most often use to identify bullets and why? | The most crucial characteristic that a firearms examiner uses to identify bullets is the striation markings due to the fact that no two barrels, even those manufactured in succession, have identical striation markings |
| List two reasons why striations on bullets fired from the same gun may vary slightly. | Striation variations on bullets fired from the same gun can occur due to barrel wear over time or the presence of grit and rust. These factors can slightly alter the striation patterns, making each bullet's markings unique to the firing conditions |
| Besides the barrel, what parts of a firearm may leave distinctive markings on a shell cartridge? | Firing Pin: Impression from the pin's shape and imperfections, Breechface: Striations from the chamber Extractor/Ejector: Marks from extracting the cartridge, Magazine: Distinct markings from loading |
| Why does a firearms examiner test-fire bullets from a suspect barrel? | When bullet is fired, rifling inside barrel creates unique striations, reflecting both class & individual characteristics of barrel, so examiners test-fire bullets through suspect barrel to obtain test bullets for comparison |
| Describe two situations in which distance determination can establish the facts of a shooting incident. | during a case where the accuser claims self-defense and in the case of suspected suicides |
| What evidence does an investigator study to make a distance determination? | unburned and partially burned particles and the distribution patterns of said particles (the closer the shot the more concentrated the residue particles) |
| How can test-firing a suspect weapon help the investigator make a distance determination? | Investigators use the suspect weapon and the same type of ammunition to create test patterns by firing at various distances onto a target material similar to the victim's clothing or skin. |
| List three characteristics of a bullet hole that indicate that the shot was fired at extremely close range. | At close range, distinctive marks around a bullet hole include heavy vaporous lead deposits, scorch marks on fibers, melted synthetic fibers, and a stellate (star-shaped) tear pattern from muzzle gases, often with a rim of lead deposit. |
| What is the Greiss test and what two pieces of information can it provide to an investigator? | detects gunshot residues (nitrites) on a suspect's hands or clothing, indicating recent gun use. It also helps determine firing distance: a higher residue concentration suggests close range, while a more dispersed pattern indicates greater distance. |
| How is shot pattern used to make a distance determination for shotgun blasts? | by analyzing the shot pattern spread. Test firings help establish a baseline. At close range, the pattern is concentrated, but it spreads with distance (1 inch per yard). Factors like barrel length, pellet size, and choke affect the spread. |
| What factors other than distance to target can affect the distance determination? | barrel length, pellet size and quantity, powder charge, and choke |
| What evidence do investigators look for when trying to determine whether a suspect has fired a handgun? Where is such evidence typically found and why? | Investigators look for gunpowder and primer residues on a suspect’s hands (barium and antimony) to determine if they fired a handgun. Residue patterns on the victim help estimate firing distance |
| Why does analysis of primer residue from a suspect’s hands produce a low rate of positive results? | due to factors like quick removal, small residue amounts, limited detection window (within 2 hours), and interference from normal activities that can spread or wipe away the residues |
| Why is analysis of primer residue typically ineffective in locating primer residue from a .22-caliber gun? | because their primers often lack barium or antimony. Even when residues are present, they are in small quantities, making detection difficult with standard methods that rely on these elements |
| Describe how a criminalist restores an obliterated serial number on a weapon. | Obliterated serial numbers on weapons can be restored through chemical etching. The stamping creates strain beneath the surface, which dissolves faster with an etching reagent, revealing the original numbers, even after grinding or punching. |
| Why would an investigator not pick up a weapon by its barrel with a pencil or stick in order to protect latent fingerprints? How should suspect firearms be handled in such a situation? | Picking up by barrel w/ a pencil/stick can disturb powder deposits, rust, or dirt lodged in the barrel thus altering the striation markings on test-fired bullets, instead handle suspect firearms by the trigger guard or grip, not the barrel |
| What characteristics of a suspect firearm should an investigator record before unloading it? | document the firing component and safety position, ammunition details, revolver chamber position, and mark each cartridge. Attach an ID tag with the serial number, make, model, and investigator’s initials to maintain evidence integrity |
| Why should the investigator number the chambers and cartridges when unloading a suspect weapon? | helps determine the order of shots, maintain accurate records, and preserve evidence integrity. It ensures clear identification, aids forensic analysis, and supports a reliable chain of custody in investigations |
| What is the investigator’s primary concern when collecting and handling bullets and cartridge cases? Why must the investigator exercise extreme caution when removing a bullet lodged in a wall or other object? | protect the class and individual markings |
| Name two types of marks that impart individuality to a tool and explain how the marks are made. | through random nicks and breaks, and microscopic irregularities. Random nicks form over time through wear and use, creating unique imperfections. Microscopic irregularities occur during manufacturing, leaving distinctive ridges and valleys |
| What techniques does an investigator use to analyze tool marks that cannot be removed from a crime scene? What is the disadvantage of this technique? | investigators use photography to capture details and silicone casting to reproduce the mark for lab comparison. However, both methods may lose minute details, reducing the ability to individualize the mark to a specific tool. |
| What is the first thing the investigator does before handling or moving any impression at a crime scene? Why is this considered merely a backup or precautionary procedure? | Before handling an impression at a crime scene, investigators first photograph it, including a scale and multiple angles with side lighting to capture fine details. This serves as a backup in case the impression is damaged before lab analysis |
| What kinds of impression evidence might a forensic odontologist be asked to analyze? How might this help identify a suspect? | analyze bite marks on skin or food, comparing them to suspects' dental impressions. They also use dental records to identify victims. Unique dental patterns can link suspects to crimes, though bite mark evidence's reliability has been questioned |
| The reason grooves are rifled into the bore of a gun is so that a: a) bullet will be made to spin & have a true & accurate course on leaving the barrel b bullet moving will have unique striations c bullet will be reduced on size before it exits the gun | a) bullet will be made to spin & have a true & accurate course on leaving the barrel |
| shoe and tire marks impressed into soft earth can be best preserved by _______ and ___________ | photographing and casting w/ dental stone |
| What are two elements detected on the hands of an individual who has recently fired a weapon? | antimony and barium |
| the higher a shotgun's gauge, the _________ the diameter of its barrel | smaller |
Created by:
hbhull05