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CRIM 355 > Firearms and Tool Marks > Flashcards

Firearms and Tool Marks Flashcards

1
Q

What is a tool?

A

Any hard object that leaves a mark in a softer object

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2
Q

List examples of tool marks at a crime scene

A
  • chisel, hammer

- footprints, blood, tire tread marks in mud

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3
Q

Name and describe the two types of tool marks

A
  1. impressed
    - tool is pressed into an object with no movement involved
  2. striated
    - tool is pressed into object and then moved (sliding motion)
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4
Q

What are class characteristics?

A
  • indicates group of tool or type of gun

- best for elimination but cannot narrow down to a single source

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5
Q

What are individual characteristics?

A
  • formed through use (accidental or planned events) or during manufacturing
  • can be used to identify a specific tool
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6
Q

How is a tool mark comparison done?

A
  • comparing like to like (ex: bullet to bullet)
  • cast or impressions are made in to make comparison with tool mark (if it can’t be removed from scene)
  • NEVER attempt to fit suspect tool in tool mark (creates/destroys evidence)
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7
Q

How is a match established?

A
  • when a significant and unique similarity exists between the test and suspect tool mark
  • class and individual characteristics agree
  • no unexplained differences
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8
Q

What are some similarities that can be found between different tools?

A
  • manufacturing carry-overs (dirt or metal chips transferred)
  • mistaking class for individual characteristics
  • random agreement
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9
Q

What are some differences found between the same tool?

A
  • rust or corrosion
  • applying tool to materials with different hardness
  • reusing tool several times after crime
  • deliberate alteration
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10
Q

What is rifling?

A
  • spiral grooves formed in the bore of a firearm barrel
  • designed to put spin on bullets to prevent tumbling
    (class and individual characteristic)
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11
Q

What are lands and grooves?

A

Lands:
- raised portion between grooves in a rifled bore
- original diameter of the barrel
- leaves grooves on bullet
Grooves:
- cut portions between lands in rifled bore
- created during rifling process

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12
Q

What is the caliber?

A
  • distance between opposite lands (expressed in inches or mm)
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13
Q

Individual characteristics of firearms

A
  • interior of barrel created by broach as scratches from metal filings and dirt
    (all gun barrel, even those made in succession, are unique due to striations)
  • individual characteristics also formed through use, cleaning, and misuse
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14
Q

Class characteristics of firearms

A
  • caliber, direction of rifling, and number of grooves
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15
Q

Why do cartridges have class and individual characteristics?

A
  • firing pin markings on cartridge (can exclude firearm)

- extractor and ejector also leave distinctive marks in cartridge shell

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16
Q

How are firearms collected from the crime scene?

A
  • need to be labelled and identified

- if found in water, must be collected with the water it was found in and do not allow it to dry

17
Q

What is gunshot residue and how is it left behind?

A
  • a fired gun leaves GSR on the shooter and target
18
Q

What can GSR tell us?

A
  • position of those involved (who fired the gun?)
  • distance between shooter and target
  • assist in determining self-defence statements or suicide
19
Q

What is required to for residue testing?

A
  • suspect weapon AND ammunition
20
Q

Contact Shot

A
  • unburned powder is forced inside wound

- skin around wound tears in star shape due to pressure from released gases

21
Q

Close Distance Shot (2.5cm)

A
  • bullet wound has rim of vaporous lead
  • unburned powder forced into wound
  • fibres from clothes may be burned or melted
  • gun may mark skin
22
Q

Shot < 30cm

A
  • halo of vaporous lead around wound

- soot and unburned powder around wound

23
Q

Shot 30-60 cm

A
  • soot no longer visible

- gunpowder particles can embed into skin

24
Q

Shot 60-100 cm

A
  • scattered specks of unburned and partially burned gunpowder grains
  • creates stippling on skin that could be permanent
  • no soot/blackening, or vaporous lead
25
Q

Shot +100cm

A
  • no residue on target
  • bullet wipe around wound (dark ring consisting of carbon, dirt, lubricant, primer reside, lead, etc.) (wipes off if it passes through target)
26
Q

How is a serial number embedded in a firearm?

A
  • stamped on the item with steel dies

- leaves a strain in the metal and crystals underneath that goes deeper than the visible serial number

27
Q

How is a serial number recovered if it has been grinded down?

A
  • using an etching agent
28
Q

In what case can a serial number not be recovered?

A
  • if it has been removed past the zone of strain or has been impressed with a diff. strain pattern
29
Q

What causes a temporary cavity?

A
  • massive stretching due to gases expanding as bullet passes through body
  • lasts milliseconds but causes tremendous damage, tears tissue, destroys organs
30
Q

What causes a permanent cavity?

A
  • crushing of tissue and bone by the bullet itself

- will heal over time, but lasts longer than temp. cavity

31
Q

Describe hollow-point ammunition

A
  • causes extreme expansion, fragmentation, mushrooms
  • creates large wound
  • not designed to pass through body (lodges)
32
Q

Describe Civilian Ammunition

A
  • unjacketed
  • used for hunting and has great stopping power
  • mushrooms, fragments (creates severe wounds)
33
Q

Describe Military Ammunition

A
  • full metal jacket
  • designed to prevent fragmenting and mushrooming
  • designed to injure, not kill
34
Q

How do police test for primer residue?

A
  • primer residue contains lead styphnate, barium nitrate, and antimony sulphide and can be detected if suspect fired gun

CRIM 355 (11 decks)

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