Target 2-4 Monday October 30, 2017 Impression Evidence Target 2-4 Monday October 30, 2017

Target 2-4 I can match impressions by interpreting individual and class indicators.

Impressions Markings left behind when 2 objects make contact with enough force Can be used to identify objects that were at a crime scene

Types of Impressions Prints show a pattern from the surface of an object Fingerprints Tire Tracks Shoe Prints

Types of Impressions Striations are scratches left on an object when another object moves past it Tool Marks Bullets

Collecting an Impression Always take photographs first Two-dimensional impressions (dust or other powders): electrostatic lift Use oblique (angled) light to detect footprints Use static electricity to stick dust to a thin plastic sheet Photograph again, and be super careful! Electrostatic lifts are very delicate.

Electrostatic Lift

Electrostatic Lift https://www.youtube.com/watch?v=Y-bxOYL7ppk

Collecting an Impression Three-dimensional impressions (mud, dirt, etc.): cast Use a precision putty to make a mold of the impression Casts are more permanent and less fragile than electrostatic lifts Can be used on any 3-D impression (including tool marks on walls, bullet holes, scratched floors, etc.)

Footprint Cast

Tool Mark Cast

Class Indicators Class Indicators are information that identifies a class or type of object Shoe size/brand Tire make/model Bullet caliber Brand of pocket knife Size of screwdriver Some classes have sub-classes!

Class Indicators

Class Indicators – Sub-classes Shoe Size Number of molds Size 6 89 Size 12 60 Size 6 1/2 69 Size 12 1/2 13 Size 7 78 Size 13 42 Size 7 1/2 49 Size 13 1/2 4 Size 8 64 Size 15 14 Size 8 1/2 75 Size 16 Size 9 87 Size 17 12 Size 9 1/2 90 Size 18 Size 10 94 Size 19 2 Size 10 1/2 83 Size 20 3 Size 11 77 Size 21 Size 11 1/2 40   Table 1: Nike Air Force I Molds (Men’s) Nike Air Force 1 Molds (Men’s) source FBI.gov

Class Indicators Class indicators can be determined based on the crime scene evidence Once we have identified a class, we can obtain warrants to collect matching objects from suspects

Individual Indicators Once we have a crime scene object AND a matching object from a suspect, we compare them for individual indicators.

Individual Indicators Individual Indicators are specific details that identify a unique object Wear marks on shoes Defects, chips, or broken pieces Bullet striations

Individual Indicators

Individual Indicators

Individual Indicators

Mini Investigation Take off one of your shoes and examine the sole closely. On one side of a clean piece of copy paper, list as many CLASS INDICATORS for your shoe as you can think of. For example: size, brand, patterns on sole Put your shoe back on and step on the back side of the copy paper. Examine your footprint and circle (use color) all the INDIVIDUAL INDICATORS you can find.