Firearms and Tool Marks

Question 1

What is a tool?

Answer 1

Any hard object that leaves a mark in a softer object

Question 2

List examples of tool marks at a crime scene

Answer 2

• chisel, hammer

- footprints, blood, tire tread marks in mud

Question 3

Name and describe the two types of tool marks

Answer 3

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

Question 4

What are class characteristics?

Answer 4

• indicates group of tool or type of gun

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

Question 5

What are individual characteristics?

Answer 5

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

Question 6

How is a tool mark comparison done?

Answer 6

• 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)

Question 7

How is a match established?

Answer 7

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

Question 8

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

Answer 8

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

Question 9

What are some differences found between the same tool?

Answer 9

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

Question 10

What is rifling?

Answer 10

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

Question 11

What are lands and grooves?

Answer 11

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

Question 12

What is the caliber?

Answer 12

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

Question 13

Individual characteristics of firearms

Answer 13

• 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

Question 14

Class characteristics of firearms

Answer 14

• caliber, direction of rifling, and number of grooves

Question 15

Why do cartridges have class and individual characteristics?

Answer 15

• firing pin markings on cartridge (can exclude firearm)

- extractor and ejector also leave distinctive marks in cartridge shell

Question 16

How are firearms collected from the crime scene?

Answer 16

• 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

Question 17

What is gunshot residue and how is it left behind?

Answer 17

• a fired gun leaves GSR on the shooter and target

Question 18

What can GSR tell us?

Answer 18

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

Question 19

What is required to for residue testing?

Answer 19

• suspect weapon AND ammunition

Question 20

Contact Shot

Answer 20

• unburned powder is forced inside wound

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

Question 21

Close Distance Shot (2.5cm)

Answer 21

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

Question 22

Shot < 30cm

Answer 22

• halo of vaporous lead around wound

- soot and unburned powder around wound

Question 23

Shot 30-60 cm

Answer 23

• soot no longer visible

- gunpowder particles can embed into skin

Question 24

Shot 60-100 cm

Answer 24

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

Question 25

Shot +100cm

Answer 25

- 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)

Question 26

How is a serial number embedded in a firearm?

Answer 26

- stamped on the item with steel dies | - leaves a strain in the metal and crystals underneath that goes deeper than the visible serial number

Question 27

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

Answer 27

- using an etching agent

Question 28

In what case can a serial number not be recovered?

Answer 28

- if it has been removed past the zone of strain or has been impressed with a diff. strain pattern

Question 29

What causes a temporary cavity?

Answer 29

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

Question 30

What causes a permanent cavity?

Answer 30

- crushing of tissue and bone by the bullet itself | - will heal over time, but lasts longer than temp. cavity

Question 31

Describe hollow-point ammunition

Answer 31

- causes extreme expansion, fragmentation, mushrooms - creates large wound - not designed to pass through body (lodges)

Question 32

Describe Civilian Ammunition

Answer 32

- unjacketed - used for hunting and has great stopping power - mushrooms, fragments (creates severe wounds)

Question 33

Describe Military Ammunition

Answer 33

- full metal jacket - designed to prevent fragmenting and mushrooming - designed to injure, not kill

Question 34

How do police test for primer residue?

Answer 34

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