ABSTRACT
As persons walk about, their shoes track over a large variety of surfaces, constantly acquiring dust, dirt, residue, grease, oils, blood, and moisture. The shoes then deposit these acquired materials back onto other surfaces they subsequently track over. As a result, they leave a variety of both patent (visible) and latent (invisible) two-dimensional impressions. On softer surfaces, such as sand, soil, or snow, they often will cause permanent deformations of that surface in the form of three-dimensional impressions. The direct physical contact between the shoe and the substrate results in a transfer of class and individual characteristics from the shoe to the impressions it leaves. The forensic footwear examiner can examine these class and individual characteristics to determine if a specific item of suspect footwear made the questioned
crime scene impression, or if that item of footwear can be eliminated. This process begins with detection and recovery of the footwear evidence from the scene of the crime, enhancing that evidence if appropriate, producing known impressions of the shoes being examined, and finally comparing the crime scene impressions with the footwear. The final result may require the footwear examiner to produce this evidence and provide his or her opinion in a court proceeding. Footwear impressions are routinely used to prove a suspect was present at the crime scene. This type of evidence is very valuable and most frequently used in homicides, assaults, robberies, rapes, burglaries, and similar crimes where the proof of an individual’s presence is, in itself, incriminating. (For a discussion of career preparation for this field, see Sidebar 15.1.)
15.1.2.1 Three-Dimensional Impressions
Three-dimensional impressions are those that remain after a shoe has permanently deformed a surface. This type of impression is typically found on exterior surfaces, such as sand, soil, or snow (see Case Study 15.1). Some of these impressions are very shallow while others may be deep. Depending on the composition of the substrate, the amount of moisture, and the presence of contaminants such as sticks, stones, and other debris, the resultant quality of the impression can range from those having great detail to those having little or no value. For instance, an impression in a clay-based soil will normally retain greater detail than an impression in a mixture of coarse sand and small rocks. Likewise, an impression in fresh snow will normally retain greater detail than an impression in wet or old refrozen snow. Three-dimensional impressions that retain sufficient detail can be identified with a specific item of footwear.
