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Forensic footwear Examiniation is the study of footwear impressions evidence created. Such evidence is used in legal proceedings to determine the identities of persons at the crime scene. Footwear evidence is often the most abundant form of evidence at a crime scene and in some cases can prove to be as specific as a fingerprint. Initially investigators will look to identify the make and model of the shoe or trainer which made an impression. This can be done visually or by comparison with evidence in a database both methods focus heavily on pattern recognition and brand or logo marks. Information about the owner of any footwear can be gained from the analysis of wear patterns which are dependent on angle of footfall and weight distribution. Detailed examination of footwear impressions can help to link a specific piece of footwear to a footwear imprint as each shoe will have unquie wear characteristics.
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Types of footwear evidence
Footwear evidence can come in at least 3 forms, footwear outsole impression evidence, footwear insole impressions and footwear trace evidence.
Footwear outsole impression
Footwear outsole impressions are impressions left on an object that was caused by contact with a piece of footwear. These can left on the ground or raised surface by persons treading over it, left on doors or walls by persons attempting to kick or climb over a wall or even left on other persons after being kicked or stomped on.
Latent footwear outsole impressions:
Latent impressions are caused impressions that are not easily visible to naked eye. Such prints can be on many different surfaces such as floor tiles, concrete or even carpet. Latent impression may not be easily visible to the naked eye and its detection may require the use of additional specialized light sources such as portable UV lighting. Recovery typically includes photography as well as lifting with "gel" or "electrostatic" dust lifters.
Footwear Insole imprints
Footwear insole imprints are imprints left in the inside of footwear caused by contact from the person’s foot. Analysis of the insole imprints can be used to link a person(s) to a piece of footwear.
Footwear trace evidence
Footwear trace evidence is trace evidence that is recovered from footwear. Types of trace evidence that could be recovered include skin, glass fragments, body hair, fibres from clothing or carpets, soil particles, dust and bodily fluids. The study of this trace evidence could be used to link a piece of footwear to a location or owner.
Detection of footwear evidence
Detection of impression in ambient lighting
Detection with forensic light sources
Detection with electrostatic lifting devices
Detection with chemical enhancement
Recovery of footwear impression evidence
Footwear evidence occurs most often as either footwear impressions left in a soft surface, such as mud or as dust deposits, which are difficult for the human eye to detect. At violent crimescenes footmarks can be left as a result of a person standing in blood and subsequently trailing it as they move around the scene.
Photography
Lifting
Footwear impressions can be lifted from surfaces with tools such as adhesive lifters, gelatin lifters or electrostatic lifting devices.
Casting
Evidence left via impressions can generally be recovered utilizing a plaster cast. Initially the impression is isolated by framing the area with a solid boundary. Following this a plaster mix can be gently poured inside the frame, it is generally considered not best practice to pour directly onto the impression. In some cases where the surface is not ideal for casting prior techniques can be utilised to gain a better cast of the impression. Sand can often be fixed in place by applying an aerosol resin or glue although hair spray is often used. Wet mud impressions can be dried using a combination of pipetting water from the surface and applying hot air, often in the form of a hair dryer.
Examination of footwear impressions evidence:
Footwear impression can be used by examiners to obtain information the following information:
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Footwear manufacturer, model and size: Examination of footwear impression for "Class Characteristics" such as general outsole patterns and shapes, footwear design features and feature markings can help examiners identify the manufacturer , model and size of the footwear. This Information can be used to help profile the suspect and provide leads on who may have bought or worn the footwear which created the impression.
Approximate height and wearer: Measurements of footwear impression dimensions can be used to provide the approximate height of a suspect. With shoeprint size information, investigators can refer to statistical data to approximate the height of the person since shoeprint vs. height relationship follows a normal distribution. Height can also be approximate by stride length which could be measured from a set of footwear impressions.
Activity of wearer when imprint was made: Analysis of a plastic footwear impression can also be used help determine the activity of the wearing when the imprint was made. The footwear imprint left by person is different when they are walking, running or carry heavy loads. A footwear impression left by running person will typically deeper in the heel and toe sections of the shoeprint. A person carrying a heavy load such as a body will cause deeper prints than a person not carrying anything.
Establish link between footwear impression and specific piece of footwear: A specific piece of footwear can be linked to a specific footwear impression with careful analysis. Every piece of footwear will show different amounts of tread wear, different amounts of damage in the form of tiny cuts and nicks. These unique characteristics will also show on the impression left by the footwear.
Limitations of footwear evidence
The Unabomber, Theodore Kaczynski, was known to keep shoes with smaller soles attached to the base in order to confuse investigators about the size of the suspect's feet [1].
Footwear databases
Forensic investigators can use computerized footwear databases to quickly compare the class characteristics between footwear impression and outsole profile of footwear outsoles stored in the database. This greatly reduced the time required to match shoemarks found at crime scenes and those from criminals in custody or those stored on the database.
By far the best system available is TreadMark, marketed by Crime Scene Investigation Equipment Ltd, Northampton, England and currently used by Police departments in the UK, Europe, USA and Taiwan. Others are avaialble such as the Footwear Intelligence Technology (FIT) launched by the Forensic Science Service (FSS) in February 2007 and SICAR but TreadMark is more versatile and has many powerful tools to help the shoemark examiner.
References
External links
- The Forensic Photoshop Blog
- Scientific Working Group on Shoeprint and Tire Tread Evidence (SWGTREAD)
