Forensic Science: Fundamentals & Investigations, Chapter 15 1 Introduction People, vehicles, and objects leave evidence of their presence at an accident or crime scene. Patent impressions are two-dimensional. Latent impressions are hidden to the eye. Plastic impressions are three-dimensional.

Types of Impression Evidence Forensic Science: Fundamentals & Investigations, Chapter 15 2

3 Shoe Impressions 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.

Forensic Science: Fundamentals & Investigations, Chapter 15 4 Shoe Wear Patterns Some factors that personalize a person’s footwear include: – Body weight. – The way a person walks. – The surface on which the person usually walks. – Debris that became embedded in the tread or unique holes and cuts in the tread.

Forensic Science: Fundamentals & Investigations, Chapter 15 5

6 Collection of Shoe Impression Evidence Photograph footprint Photograph footprint with ruler or measuring tool for court testimony Three dimensional footprints are casted: using material that fills impressions and then hardens to capture impression image.

Forensic Science: Fundamentals & Investigations, Chapter 15 7 Tire Treads and Impressions To channel water away and provide traction, a tire’s tread is divided into ridges and grooves. Tires can leave patent, latent, or plastic tread patterns. Tire evidence usually indicates the type of vehicle that left the mark, may be used to link a suspect or victim to a crime scene, and can reveal the events that took place.

Forensic Science: Fundamentals & Investigations, Chapter 15 8 Recording Tread Impressions Ridges and grooves of discovered tire impressions are counted across the entire width. 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. Comparison with impressions from the crime scene, then, can be made.

Forensic Science: Fundamentals & Investigations, Chapter 15 9 Identifying a Vehicle Identifying tread patterns may not be enough to link a suspect with a crime scene. Other things can help with this: – Front and rear track widths. – Wheelbase measurement. – Turning diameter. Databases can be checked to find the vehicle with these specifications.

Forensic Science: Fundamentals & Investigations, Chapter Accident Reconstruction Drivers may not recall the exact series of events before, during, and after an accident. People, vehicles, and objects, however, can leave evidence of their actions at the scene of an accident. Debris patterns and tire marks, for example, can be clues to speed, direction, and vehicle identification.