2. Types of Impressions 1.Latent Impressions: hidden impressions requiring special techniques to be visualized. 2.Patent Impressions: 2D impressions that are already visible 3.Plastic impressions: 3D impressions cast in soft materials, such as soil and snow or blood

3. What is impression evidence? Let me explain… Impression evidence can be defined as objects or materials that have retained the characteristics of other objects through direct contact. Impressions are created when one object is pressed against another material/object with enough force to leave an imprint of its shape.

4. Collecting the evidence Things to remember….. Take photos as soon as possible. Take multiple photos of the impression from at least two different orientations. Place an identifying label and a ruler in position with the impression for the photo. Use oblique lighting when possible.

5. How do we collect latent impressions? Glad you asked….. You must make the print visible by using one of the following techniques: Saturating the print with luminol which will make bloody footprints glow in the dark. Dusting the latent print reveals an impression. Electrostatic lifting and gel lifting (impression shown below) techniques also can capture hidden impressions. Casting

6. Electrostatic dusting and lifting? Sure I’ll explain…. Electrostatic dusting can reveal dust left with each step and create an impression. Electrostatic charges can lift impressions from paper, carpeting, wood surfaces, linoleum, asphalt, and concrete. Other methods to recover latent impressions include gel lifters. These methods can provide information about the person who left the shoe print.

7. Most popular and successful method is the use of snow print wax Available in a spray can Results in fragile, thin cast that shows great detail After drying is filled with dental casting mixture Paint thinner, spray paints, paraffin and sulfur can be used as well

8. Plaster of Paris Soft, even after drying Made up of large particles that may cause the loss of crucial detail Require the use of forms and reinforcing materials Dental plasters and stones Dense, uniform, smaller particle size Quick drying and show more detail Expensive

9. What’s the 411? Information we can gather from footprints… The size of a shoeprint can tell the size of foot of the person. The depth of a foot or shoe impression can tell something of the person’s weight. The type of shoe can tell something of the person’s job or personality. Databases contain the names of specific manufactures and tread patterns used to identify different types of shoes. Debris that became embedded in the tread or unique holes and cuts in the tread

10. What’s the 411? All about tire tread evidence… Usually found in road accident scenes or in the access and escape routes of other crime scenes Tracks help investigators identify the type of vehicle that left them. Tires can leave patent, latent, or plastic tread patterns. May be used to link a suspect or victim to a crime scene, and can reveal the events that took place. *Tire databases are available help investigators determine the brand and model of the tire that left the impression, which can be used to determine the type of vehicle that made the tracks.

11. How do you record tire impressions? It’s simple…. Ridges and grooves of discovered tire impressions are counted across the entire width. Analyze 1. Tread Pattern 2. Width & depth of the tread pattern Unique characteristics such as wear or pebbles embedded in the grooves are noted. A print of a suspect’s tire impressions (through one revolution) is taken.

12. After the evidence is recorded…. Identify the vehicle Identifying tread patterns may not be enough to link a suspect with a crime scene. Other things can help with this: 1. Front and rear track widths. 2. Wheelbase measurement. 3. Turning diameter. Databases can be checked to find the vehicle with these specifications.

13. There are three basic types of tire marks:  Skid marks—can be clues to the distance when brakes were applied and the vehicle’s speed.  Yaw marks—can show a sideways skid.  Tire scrub—can determine the area of impact. How are each of these formed?

14. Applying your knowledge Conduct a case study The O.J. Simpson Case The Meredith Kercher Case Lacey Rutheford-Coos County Russell Williams 2010 Cecil Sutherland United States V Allen