Tool, Tire, and Tread Marks/Firearms P1 Flashcards
Toolmark
any cut, impression, scratch, or abrasion created by a tool acting on a softer surface or object
Source of a toolmark
the object that made it
Substrate
the surface or material in which the toolmark is made
Compression
occurs when a tool makes direct contact with a softer substrate
Sliding
occurs when the tool moves along the surface of the substrate
Cutting
occurs when a tool is used in an attempt to perforate through the substrate
If enough force is applied,
the impression of the tool is made as the surface of the substrate is compression
Sliding usually results in
a series of parallel striations
Cutting is a combination of
compression and sliding
Ways of collecting toolmarks
Collect the object with the toolmark.
Cut the toolmark area from the object.
Make a cast of the toolmark.
Casts of toolmarks are usually made with….
Mikrosil
The variations of non-firearm related toolmarks can be separated into
orientation of the object, force, substrate type, and number of marks
What is typically used for making casts of shoe and tire impressions
Dental stone
How are dust prints deposited?
When a foot or shoe becomes contaminated with a foreign material and that material is transferred onto a surface
Rubber lifter
uses a sticky surface and is placed over the print, then lifted from the surface
Photographic paper method
involves laying black or white photo paper (depending on the colors of the surface and print) onto the print surface
Electrostatic Lifting Apparatus
produces a mirror image of the processed print
Characteristics in the tire impression that should be noted
Tread design
Wear bars
Noise treatment
Accidental marks or variations
Wear bar
a raised rubber bar 1/16 of an inch above the base of grooves on a tire
Tread design
the part of the tire that contacts the road and has a design specific to a model of tires
Accidental marks/variations
specific marks created either in the manufacturing process or by the process of wear
Where are three dimensional shoe impressions generally made?
Soft exterior surfaces, dirt
When a crime scene impression corresponds in both design and physical size of that design with the suspect’s shoe, the association has a ___ evidentiary value
high
_______ impressions are collected from victims, police officers, or medical personnel so that they can be accounted for if similar impressions are found at the scene
Elimination
A footwear impression of what origin can be lifted using electrostatic lifting?
Dry
The _____ track width will always record accurately, so this tire track should always be obtained at crime scene
Rear
Sometimes a ______ is used to help visualize impressions for digital imaging
Developing Reagent
What kind of lighting can be used to search for faint impressions?
Oblique Lighting
The main features that distinguish one pair of shoes from others of the same size and style are collectively called ____________
Accidental Marks
SoleMate® is an example of a _____ of shoeprints
commercial database
Dental stone can be used in snow, but only if _____ is applied first
Insulating wax
When comparing impressions, what area is normally the first aspect to be examined?
Sole design
2D impressions
Indoors, hard surfaces
3D impressions
Plastics; outdoors in soft surfaces
What methods are used to enhance footprints?
Oblique lighting and LCV
Impressions
Show tread design and dimensional features of individual tires
Tracks
Shows relationships between tires
Deposition of rubber tells us
The vehicle was skidding
Tire tracks give us….
Track width
Turning diameter
Path history
What are some ways we can collect tire impression evidence?
Examination photograph
Cash with dental stone
Exemplars of tire treads are always..
2D
What are class level characteristics of tire tread marks?
Number and shape of ribs
Slant and size of grooves
Arrangement of design elements
For flat objects, we need ____ for an identification
one group of 8 CMS or 2 groups of 5
What should be analyzed with the comparison microscope?
very small items
When analyzing shoe prints, there may be a gap between the front and back of the impression, due to a structure called the
shank
How should dust footprints (on smooth surfaces) be collected?
ESLA & gel lifter
3D casts of footwear - either exemplars or evidence - are made with _________________
dental stone
Which of the following methods would be ideal for identifying the source of a footprint?
Comparing a ESLA dust lift to an inked exemplar
Place the steps of tire impression casting in the correct order
Photograph the impression, overlapping as necessary
Prepare the mold and liquid dental stone
Pour the dental stone into the mold
Mark with caster’s initials or ID #
Allow to harden completely
Tire analysis is different from footwear analysis in which way?
Tires are most frequently compared using a 2D exemplar to a 3D casting
Class characteristics are more difficult to determine from ____ tool marks than other types
sliding
What components of a firearm can mark a cartridge case in forensically useful ways?
Firing pin
Ejector
Breechblock or Breechface
caliber
approximate diameter of a rifled barrel
Compared to other types, _____ bullets are best marked by the rifling of a barrel
lead
A comparison microscope consists of two light microscopes connected by a(n): __________
optical bridge
What force typically moves the slide or breechblock back to the cocked position after a semiautomatic pistol is fired?
Energy produced by the fired cartridge
Shooting distance determination depends on comparing the ________ on artificial targets to the evidence collected at the scene
residue distribution
Elimination and comparison images are collected using
compressible foam
Stance
track width
wheelbase
measurement between the centers of the hubs of the front wheels to the centers of the hubs of the rear wheels
