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 09 Dec 2019      Forensic Science
We have mentioned about Locard’s Exchange Principal before, “Perpetrator of a crime will bring something into the crime scene and will leave with something from it”. Footwear prints and Tire tracks are “pattern evidences” and are great examples of this principal, even though these evidences might seem “very generic” or “misleading” it can give us many information regarding the vehicle used, the shoe size of the perpetrator, even the weight of the vehicle and the perpetrator in some cases. The footwear and tires can carry other materials from the perpetrators environment and create a print/track in the crime scene, these prints are called as “imprints”.

Figure 1. Tire Tracks on Snow

Figure 2. Impressions on Soil

Photography with a qualified device has a great importance in footwear and tire track investigations. To identify these prints and tracks, forensic scientists can use certain databases compiled by the shoe and tire manufacturers to match with photographs and analyzed patterns from the crime scene.

A very basic theory is used in the analysis of these prints and it is almost like fingerprint analysis with some important differences.

Shoes or tires can create visible, three dimensional impressions on softer surfaces such as sand and soil but when faced with a hard surface such as wood, asphalt or concrete, they create imprints instead of impressions. These impressions and imprints can be compared to the suspects footwear or vehicle. Other than basic impressions and imprints, these objects (Footwear and tires) can have wear and tear markings on them and these markings will provide a great deal of information about the perpetrators and their vehicles to the forensic scientist, these can be about;

· If the perpetrator was on foot or with a vehicle?

· What type of vehicle the perpetrator used?

· What kind of shoes perpetrator wears?

· Which way the perpetrator went or which way he/she came from?

· In case of homicides, If the body was moved?

· Number of vehicles in the scene or number of people at the scene

· Location of the crime.

Lets take a shoe sole as an example, it can have specific wear and tear markings or erosion in the pattern depending on the material, use of the shoe and certain characteristics of the wearer, forensic scientists can understand if the perpetrator is physically disabled, overweight or limping by looking at the shoe print or the distribution of the prints in the crime scene. A car with an out of way tire alignment can cause specific tires to wear differently, this way the forensic scientist can understand if the car has wheel alignment issues and which side has the alignment issue. Tires can get damaged over time and these damages will cause specific patterns on the tires and these patterns are mostly one of a kind, this way, the matching will be more trustable.

There are 3 main characteristics searched in a print,

Class Characteristics:

General Class Characteristics:

Standard characteristics of every item produced by the company, as an example; shoe soles of a specific model of a shoe is the same throughout the market.

Limited Class Characteristics:

Certain molding errors or use of slightly different molds in the manufacturing process can yield a produced party special, same brand, same model shoes or tires can produce different prints occasionally, some of these differences are logged in to databases.

Individual Characteristics:

Unique characteristics of a tire or a shoe print caused by using the item, these can be changes occurred by something stuck between the treads or crack, cuts and damages from the environment.

Wear Characteristics:

These are also unique characteristics caused by use but these characteristics occur because of the, properties, errors of the car or the situation of the wearer such as disabilities, injuries, weight, walking pattern and where they walk.

These characteristics are researched and compiled in international databases by forensic scientists and manufacturers, and these databases are utilized in the analysis process.

Figure 3. Tires with different patterns and different wear and tear characteristics

Figure 4.Tire With Specific Crack patterns

To clarify these, I would like to mention a very important case in the history, 1995, The murder of Nicole Brown Simpson and her friend Ron Goldman. O.J. Simpson, former NFL player and actor was tried for the murders, even though Simpson was acquitted from the crimes and the crime remains unsolved to this day because of other legal issues, there were a very important discovery during the investigations, Bloody shoeprints from a very specific pair of shoes, an extremely rare and expensive Bruno Magli shoes, only 29 pairs of these shoe were sold in the US at the time and the size 12 (Eu:46) was a perfect match for O.J. Simpson. O.J. Simpson denied that he had these shoes and no evidence was found regarding the purchase of the shoes but in 1996, a key evidence surfaced, the photos of O.J. Simpson wearing the shoes in an event in 1993 putting him at the crime scene…

Figure 5.O.J. Simpson Case, Crime Scene

Figure 6.FBI evidence from the O.J. Simpson Case

How the evidences are detected and collected?

To explain this, I should mention how are these evidences are categorized. There are three different types of foot/tire marks can be found in a crime scene,

· Visible

· Plastic

· Latent

And these can be collected from everywhere, from wood to sand to the body of the victim.

Visible prints occur with a transfer of material from the tires or the shoes to the surface with their specific patterns. These prints are visible to the naked eye but additional light sources and special devices such as ForenScope Multispectral Tablet, 4K Multispectral Tablet or Contactless devices can be utilized to increase the quality of the evidence and to photograph the evidence.

Figure 7. Bloody Shoe Print

Plastic Prints are three dimensional impressions, these are left on soft surfaces such as sand, dirt, mud or soil.

Figure 8. A plastic print in snow with Blood evidence

Latent Prints are normally non-visible to the naked eye and certain chemicals, powders or devices can be utilized to render them visible, though powders and chemicals are harmful to the valuable evidence and not practical, using special light sources and multispectral equipment is at upmost importance, in these cases ForenScope multispectral technologies can be utilized to detect and collect evidence with ease because of their portability, unique technology and ease of use.