Topic 9 Flashcards
Traces left by a criminal in the form of foot impression, tool impression and tire impression in cases like theft, robbery, etc. will be studied in this chapter. The evidential value of an impression made by shoe, hand, tool or other articles is based in the theory that no two physical objects are alike and hence that impressions made by such object often is marked by uniquely identifying characteristics. A given impression can only be produced by one object.
TOOLMARKS AND IMPRESSION
– a strong mark produced by pressure that goes below the surface. A stamp, form or figure resulting from physical contact. It causes damage to object.
Impression
– weak mark made by pressure that stays on the surface. In scientific criminal investigation the problem of reproducing the faithful representation of an object is of great evidential value. In many cases reliance has been placed on photographic method. In cases involving footprints, tool marks, tooth impressions, photographic representation may not serve the purpose. Using a mold called moulage can only make a faithful reproduction of these objects.
Imprint
– a faithful reproduction of an impression with the use of casting materials. It is admitted that moulage cannot reproduce all characteristics of the object under all circumstances but whatever is mission in a moulage it can be supplied by the photograph.
Moulage
– any material which can be changed from a plastic or liquid state to the solid condition.
For foot impression and tire impression, Plaster of Paris is the best casting material. Sometimes it is desirable to hasten or retard the setting time of the Plaster of Paris.
Casting Material
Results when a tool is pressed against a softer surface;
Tools usually leave distinctive marks;
The hardest of a tool influence the resulting mark left in the softer object;
May indicate the size of the tool used in a crime.
Indentation Marks
An object’s surface can be ground or worn away by a tool when they slide across each other;
The harder object causes abrasions on the softer surface;
Indention and abrasion marks sometimes occur at the same time.
Combo: the object is both inserted and dragged across the surface.
Abrasion Marks (scratches):
Edge instrument can penetrate a softer object and separate it int o parts;
Cut marks are prooduced along the edge as a surface is cut;
The type of saw blade can be determined by examining the cut surface of the bone.
Cutting Marks:
Often there are no witnesses at a crime and no cameras to capture what happened, so detectives must rely on evidence to figure it out.
Impressions made by shoes, bare feet, teeth, tires, and other objects are helpful because they can form impressions and leave clues.
CAST AND IMPRESSION
Visible, two-dimensional marks formed from soil, dust, paint, blood, ink, etc.
Patent impressions
- Hidden to the naked eye but can be visualized through the use of dusting or electrostatic techniques.
- Like latent fingerprints, they are often caused by oils or microscopic dirt particles depositing on a surface.
Latent impressions
Three-dimensional imprints left in pliable materials such as snow, mud, soil, or soap.
As a result of the soft substrate, these prints can often be lost (melt or blow away) and should be photographed immediately.
Plastic impressions
a. Databases contain tread patterns used by different manufacturers, and can often be traced down to retailers which sell the shoe.
b. A shoe impression can help an investigator determine the foot size and the possible height and weight of a person.
c. While many people may wear the same shoes, each person wears down his or her shoes differently, based on their gait, or walking pattern. Shoe wear patterns can help individualize evidence.
d. If numerous prints are found at a scene, detectives can gain information about:
the number of people at the scene;
Movements of individuals at the crime scene;
The entrance and exit to the scene.
SHOE IMPRESSION
