Impression evidence Flashcards
What is a positive impression?
Imprint from a shoes or tire depositing material onto a recipient surface
What is a negative impression?
Imprint that removes residue from the recipient surface, leaving behind a clean image of the print
What material is used to cast 3D impressions? Why is it used?
Dental stone. It is light and dries quickly but is fragile
What is used to cast 3D impressions in snow?
Snow print wax, a bright red or brown spray that creates a thin casting
What is used to lift imprints?
Tape or gelatin materials, electrostatic lifting devices, contrasting colour film
Why are tire impressions difficult to lift?
Typically long, leading to bulky and large casts. Also commonly on a steep incline
What type of impression is obtained from casting tread marks?
Negative impression as the raised area of the tread becomes depression in the cast
What can tire impressions reveal about the vehicle?
Wheelbase, distance from front hub to rear hub, and tire tread stance, distance from centerline of left to right tire
If the metal under serial numbers is denser than the surrounding metal what happens?
The numbers are raised as they dissolve slower than the surrounding metal
What is an indicator of a contact bullet hole?
Severe damage to the target and uneven edges on the bullet
What indicates a bullet was shot more than 3 inches from the target?
The presence of bullet residue, composed of lead, primer and carbon
What is the Modified Griess test to detect gunshot residue?
Using a piece of photographic paper treated with sulfanilic acid, distilled water and alpha-naphthol methanol. Residue appears as orange dots
