10. Impression Evidence

10. Impression Evidence Impression Evidence • Objects or materials that have retained the characteristics of other objects or materials through direct physical contact. Types of Impression Evidence • Shoe prints, Tire tracks, Toolmarks, Fabric impressions, Weapon impressions. Recognition & Detection • Based on other evidence at the scene, determine most likely places for impressions. • Use oblique lighting & ALS to visualize impressions. • Use electrostatic lifting techniques to detect & life latent impressions (after scene documentation). Inked Shoe Prints Terminology • 2-D Impressions: Have length & width, but no depth • Positive Impressions: Residue visually represents the areas of the sole that came in contact with the surface. • Negative Impressions: Contact areas of the sole remove residue from a surface. • 3-D Impressions: Have length, width & depth. • Dry Origin Impressions: Shoe & substrate are dry when impression is made. • Wet Origin Impressions: Shoe and/or substrate are wet when impression is made. 2D Positive Impression evidence/"https://aboutforensics. 3D Impression Documentation • Notes, Sketches, General crime scene photography, examination quality photography. Enhancement & Collection • Electrostatic lifting techniques, Adhesive lifting, Blood, Dust, Soil enhancements, Powdering, Casting techniques Making Test Impressions • Ink on paper • Powder dusting and adhesive lifting • Identicator • Transparencies: Photocopy test impression or actual tread pattern Dental Stone Casted Shoe Print Class Characteristics • Characteristics that are shared by at least one other item. • Many are part of the manufacturing process: Size, spacing, tread design, etc. Individualizing Characteristics • Characteristics that are unique and random. • Can establish a link between a questioned impression and one object. Wear Characteristics • Changes in the surface of an object due to the erosion of portions of the surface. • Not individualizing, since it is possible for two or more people to wear out the sole in a similar manner. Casting Materials • Dental Stone: Bulk, Premixed with Water