Toolmarks Flashcards
Definitions
Tool - an object used to gain mechanical advantage
Toolmarks- any impression, cut, scratch, gouge, or abrasion caused by a tool coming into contact with another object
How do you identify tool marks?
A discipline in forensic science where the primary concern is to determine whether a tool mark was made by a particular tool
Based on
- Class characteristics
Features that are common to a group of objects
- Individual characteristics
Characteristics that are unique to a given object
- General wear and tear
- Marks produced by the random imperfections or irregularities of the tool surface
- Caused by corrosion, wear or damage
What are the types of tool mark impressions that can be made?
Static
Tool is pressed into a softer material and leaves an impression - involves pressure
Dynamic
Tool slides or scratches across a surface - involves movement
Cutting
Pressure is applied on both sides of an object
Can leave marks and striations along the cut edges
Multi-stroke
Caused by repetitive actions
Explain tool classification and its sub categories
Tools can be classified by their design
They are sorted into:
Pliers
- Locking
- Long nose
- Slip joint
- Groove
Cutters
- Diagonal
- Wire
- Circular
- Bolt
Wrenches
Chisels
Hammers
Screwdrivers
What are the characteristics for pliers?
Class characteristics include
- Jaw width
- Jaw length
- Teeth spacing
- Jaw lip length
- Number of teeth
Locking pliers
- Vice-like grips and opposed jaws
- Used for grasping and locking onto an object
Class characteristic: teeth spacing
Long nose pliers
- Longer jaws, often narrowing towards the tips
Slip joint pliers
- Adjustable pliers which can be opened to two different widths
Groove pliers
Explain the features of a monkey wrench
Jaws hold two sides of an object
Jaws are tapered slightly inward
Jaws tighten on the object as the wrench is tightened
Explain a hammer and its features and types
A hand tool with a heavy rigid head and a handle designed to deliver a force to an object by striking it
Features:
Peen (or claw)
Handle
Grip
Head
Eye
Cheek
Face
Neck or throat
Types of hammers
Sledgehammer
Cross peen (pein)
Ball peen (pein)
Jeweller’s
Upholstery
Veneer
Mallets
Claw hammer
Geological
Bolt Cutters and Wire Cutters and Diagonal Cutters
Bolt cutters
- Cut steel rods or bolts
- Pivot action
- Maximal force
Wire cutters/ Strippers
- Multifunction tool
- Strip plastic insulation from a wire
- Cut the ends of wires
- Class characteristic - flat surfaces
Diagonal Cutters
- Designed to cut metal, often wire
- Pinch metal between cutting edges
- Class characteristic - roof-top shape
Chisels
Bladed tools designed to compress material when struck
Bevel - angled area from tip to blade face
Class characteristics
- Blade width
- Blade thickness
- Bevel thickness
Screwdrivers
Tool designed to turn screws
May also be used to pry open objects
Class characteristics
- Blade width
- Blade thickness
- Surface texture
Crowbar
Used to pry open or lever objects
Class characteristics
- Size
- Claw size
- Shape
Circular Cutting Tools
use a rotating edge to remove material
Most common type is a drill
Drill bit uses the edge to cut the material
Waste (swarf) is drawn away from hole by the flutes in the drill bit
Class characteristic - diameter
Drill bit manufacturers may use different designs to improve the cutting ability of the bit
Designs will have different class characteristics
Tool Mark impression recovery
- Photograph/sketch
3 shot rule (Overview, midrange, closeup)
Always use a scale
Lighting - Take to lab
or - Cast using silicone, plaster or clay - if item cannot be removed from the scene
Never attempt to fit the suspect tool into the tool mark
Any contact between the tool and the mark may alter the features/details of mark and raise serious questions about the integrity of the evidence
What materials are used for casting?
Dental stone
- very fine grade calcium sulphate (gypsum or plaster of Paris)
- used for bite marks, footwear marks, tyre marks
- chromatic dental stone changes colour, indicating when to apply the paste and when it has set
snow
- waxy substance (Snow Print Wax) is sprayed over the impression before the dental stone is poured in
Provil
- Permlastic/Polyvinylsiloxan
Used to take impressions of smaller objects like bite marks or scratches on a forced lock
Both products consist of two tubes (base and a catalyst) which are connected so that equal amounts of each are dispensed
Two components are mixed and the resulting paste is applied to the impression
Isomark
How to package evidence - toolmarks
Package the suspect tool and the tool mark in separate containers
Avoid contact between tool and mark
Avoid contact between tool or mark or any other hard surface
Failure to properly protect the tool or mark could result in the destruction of individual characteristics
