Foot Prints and Impression Evidence in Crime Scenes
Each and every inch of a crime scene may contain materials and evidence that can help solve crimes. Crime scene investigation includes the documentation and processing of evidence including bodily fluids, finger prints, weapons and tools, and sometimes, even the details of the size, style or brand of a shoe of a potential criminal. With the abundance of information available from researchers and forensic investigators who are linking DNA evidence to crimes, many of the older techniques for crime scene investigation may seem outdated. However, when there is no DNA evidence to link a criminal to a crime, or the criminal has no information retrieved from former crimes, it’s the older techniques of evidence collection and documentation that are relied upon in order to discover, indict or prosecute an alleged criminal.
With Impression Evidence, evidence created when a hard object pressed against softer material, leaving an impression, such as grass, mud, and paint around a window or car that is part of the crime scene. This evidence usually falls into three different categories: foot prints or shoe impressions, tool markings or tire tread impressions.
The foot prints that are found in crime scenes generally fall into three of their own categories: visible, latent or plastic. Visible foot prints are those that can be seen by the naked eye, usually due to the criminal walking through materials, blood or other substances and then stepping on a flat surface like a tile floor or patio. These prints are unmistakable as part of the crime scene because they literally contain parts of the crime scene. Latent foot prints are similar to visible foot prints in that the criminal had to walk through crime scene materials, but the materials themselves may not be detected upon a regular inspection, and special lighting and dyes may be necessary in order to see the full foot print. In order to process both of these types of foot prints, the evidence is photographed and sometimes transferred onto plastic or other materials in order to be catalogued as evidence.
Plastic foot prints are those that normally occur outside, such as a shoe print left in mud. Plastic foot prints are also the prints that are used with castings, as photographs are less likely to include as much detail as a replica of the print itself. Most castings are created using materials such as Plaster of Paris, paraffin wax or, most commonly, dental stone.
As any educated Crime Scene Investigator will testify, the majority of clues within a crime scene go undetected by those not trained in crime scene investigation. It is common for investigators to rely on the evidence collected through blood, hair or other DNA samples as a way to identify criminals or link them to crime scenes. When those samples are absent or there is no criminal information that matches the samples, it’s the tangible evidence collected by a crime scene investigator that begins to paint a picture of the crime’s timeline, events and even its perpetrator.