Crime Scene Investigator Network Newsletter

Introduction
Questions concerning the time elapsed between the collection of shoe impressions at the scene and the collection of a suspect’s shoes are commonly heard by shoeprint analysts. A review of the literature has failed to uncover previous studies that attempted to answer these questions. It is not known exactly how much time can elapse before identification is impossible between a questioned impression and a suspect’s shoe. It is dependent on several factors such as how often the shoes are worn by the individual and what surface is stepped on. Obviously, someone walking on rough surfaces will acquire more marks on the bottom of his or her shoes in less time than someone who is always walking on a smooth, carpeted surface. An analyst performing shoeprint identification can expect some differences between the questioned impression and the suspect’s shoe if there was any significant interval between the time the impression was made and the shoe was confiscated. The degree of difference, however, is dependent on what occurred between those two events. Shoeprints can be linked to a person’s shoes by comparing such general characteristics as the shoe’s class characteristics, wear pattern, and individual characteristics.

Class Characteristics
Class characteristics are marks that are a direct result of the manufacturing process of the shoes [1]. These marks may be intentional or unintentional. The important fact to remember is that they are repeated on the sole of each shoe that is made. For instance, an athletic shoe will have a certain tread design on its sole. Most athletic shoes that are made these days have their tread pattern designed by a computer program using modern CAD-CAM techniques [2]. This generates a computer file that produces a mold of the same design every time. This mold can then be altered, thereby individualizing it from other molds. For example, a worker can repeatedly hammer one area of the metal mold to produce a stippled region. This imparts a random texture onto the metal mold. Another alteration that is commonly seen is the interchanging of logos so that more than one shoe company can use the same mold. This is important because it individualizes each mold. The mold subsequently forms the rubber into the shoe outsole and thus each shoe produced from that particular mold will be identical when new.

Wear Patterns
Wear patterns are defined by Bodziak as the erosion of the outsole due to frictional and abrasive forces that occur between the outsole and the ground [1]. Over time, these abrasive forces wear down the material on the bottom of the shoe, resulting in a lack of, or alteration of, the original sole design in certain areas of the shoe’s sole. Wear patterns play an important and underutilized role in the analysis of footwear impressions. The degree of wear is important in comparisons when there is significant difference between the shoeprint and the questioned shoe. Another important factor in wear patterns is the position of the wear.

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