Footwear Impressions

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Footwear impressions are commonly left at Crime Scenes, and should always be looked for.  However, they are not always visible at first. 

 One of the key methods to look for such impressions is with the use of a technique called oblique lighting.  

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By directing a flashlight at a low angle with the surface, you create a shadow or reflection for all the dust/dirt/debris on the surface.  In doing so, you may often make footwear impressions visible, which were not visible before. 

Footwear Impressions

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Once discovered, the impressions may be developed in a similar fashion to friction ridge impressions, with the use of powders or chemicals.  

What you look to develop and document is the class and accidental characteristics which may be present in the impression. 

A key to the documentation is to photograph from directly above, with light coming from a variety of angles all around the impression.  This is a key for both two-dimensional and three-dimensional impressions.  

And, for three-dimensional impressions, you may also be able to cast, and create a three-dimensional artifact from the impression.  

3-D Impression

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This impression was created with Dental Stone, which is a technique to consider if you have a three-dimensional footwear impression at a crime scene.  

Footwear Impression Chemical Enhancement

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At times, there are also chemical techniques you can use to enhance the visualization of the impression details.  Ultimately, this will depend on what the matrix is that makes up the impression.  

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Here is an impression in blood, which was enhanced using Leuco Crystal Violet. 

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Are Footwear Impressions Unique?

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From a forensic perspective, footwear impressions do not differ from fingerprints in level of uniqueness.  But the difference is in the persistency. 

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The uniqueness of footwear impressions is created by random pressures on the outsole of the footwear during construction, or regular wear and tear. But the persistency of these specific random and unique features can change over time, unlike fingerprints. Nevertheless, they are still a key piece of evidence to look for during all forensic investigations.