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Owen McDonnell

“Wherever he steps…” with those words in 1953, Paul Kirk began his explanation of Locard’s exchange principle, which has become a mantra for forensics. His principle holds the promise that evidence is there; we only must find it, study it and understand it. 

Most fingerprint examiners know that Mark Twain foreshadowed the use of fingerprint testimony inPudd’nhead Wilson.” Twain also wrote about footwear impressions in “The Adventures of Huckleberry Finn.” In that novel, Huck knows Pap has returned when he sees a boot print with a nail head forming a cross in the left heel print.

As crime scene investigators, we must be cognizant of Locard’s principle. In “Footwear, The Missed Evidence- A Field Guide to the Collection and Preservation of Forensic Footwear Impression Evidence,” Dwane S. Hilderbrand refers to footwear as the missed evidence. I’m not sure if it’s missed, forgotten or just overlooked. Granted, no one ignores a bloody shoe print on a homicide, but do we actively search for footwear impressions in other crimes?  If we don’t, we may miss important evidence. When footwear impressions are found at the scene, an abundance of information may be available, including the number of suspects present, the path and movements leading inside and exiting the scene.

As with other types of impression evidence, three basic types of footwear impressions are found on crime scenes: visible, plastic and latent. Visible impressions can be seen without additional aids. They are comprised of a transfer of residue (i.e. blood, mud, dust) on the shoe to the surface. Plastic impressions are three dimensional and are found in soft surfaces such as soil, wet paint and snow. Latent impressions are not readily visible with the naked eye without lighting or development techniques.

Search for impressions using low oblique lighting. Always use general photography and documentation. Comparison quality photography at a minimum of 1000 ppi should always be conducted prior to employing other collection techniques. The camera should be mounted on a tripod, and a scale must be included in each comparison photograph. Without a scale, you cannot conduct a 1:1 comparison. The back of the camera must be parallel to the impression. Multiple exposures and lighting from different directions can help capture high levels of detail.

The method used to collect the impression is dependent on which type of impression is found and where it is located:

  • Traditional adhesive lifter materials are best suited for prints on smooth surfaces such as hardwood floor or tile, when used in conjunction with prints developed with fingerprint powder.
  • Gelatin lifters, which are sheets of rubber with a low adhesive layer on one side, can be used on almost any surface, including porous, rough and textured surfaces. The low levels of adhesive allow it to release from surfaces without damaging them.
  • Three-dimensional impressions can be captured by casting. Modern commercial casting stone materials provide high-quality reproduction of detail.
  • Electrostatic dust lifter can be used on dry or dust impressions on either porous or non-porous surfaces. It works by placing a lifting film over the impression. An electric charge is applied to the film and the surface transferring the impression to the lifting film.

Individual footwear impressions are comprised of several types of information. Class characteristics are the first information observed and include general shape, length and width, tread design, heel design and other general characteristics. If the quality of the impression is sufficient, class characteristics can be used to quickly include or exclude possible sources. If class characteristics are consistent, the examination moves to a comparison of individual characteristics, which are acquired as footwear is worn, and include wear patterns and random defects such as nicks and cuts.   

In considering tread design, remember that it’s common practice for multiple manufacturers to use the same outsoles. In addition, individual companies may limit the use of the design to one specific shoe model, or they may use the same design on more than one model. With athletic shoes, often the outsole is distinctive to the brand, and occasionally the model may be visible in the impression.

Despite potential challenges posed by overlapping uses of outsoles, the outsole pattern may provide significant investigative leads. Many law enforcement agencies maintain databases of outsole impressions. Commercial databases include the Everspry, available in U.S through Evident, and Foster and Freeman’s SoleMate systems. These databases are searchable and can provide results, including when the outsole is used on more than one brand or model.

The Advanced Forensic Science Research class at Webster Groves (MO) High School maintains one of the most surprising databases. Under the guidance of Jeannette Hencken since 2001, students have collected approximately 150 different shoe impressions twice each year at Payless and Walmart stores. The students record manufacturer, model name, model number, and date of collection. They maintain a website for use by law enforcement, with the last four to five years of images available. Older impressions are not available on the website but students may conduct searches upon request as time permits. While the students are not footwear examiners, they may also be able to help in searching online for outsoles not sold by Payless or Walmart. Agencies from around the world have contacted this group, and the students have assisted agencies at the local, state and national levels. When Hencken retires at the end of May 2018, Mebbie Landsness will continue this endeavor with the students. The group can be contacted at forensicswghs@gmail.com.

The next class characteristic to consider is size. Keep in mind that the measured length of a footwear impression is related to, but is not the same as, the shoe size. Footwear sizing is based on a fixed ratio between the measured length and width of the foot. Outsole length will be longer and wider, and varies based upon the design of the sole. For example: Western wear boots, work boots, and hiking boots of the same size will have different lengths and widths.

Conducting footwear examinations beyond a cursory visual examination of class characteristics requires an extensively trained footwear examiner. Most state crime labs offer footwear comparison services. If this service is not available, there are private consulting companies that will conduct fee-based examinations. You must submit recovered impressions and the shoes for comparison for the examination. Conclusions rendered by footwear examiners range from an individualization or elimination to inconclusive or association. Inconclusive results when there is not sufficient information present in the crime scene impression to render a definitive conclusion. Association occurs when class, wear and some individual characteristics agree, but a sufficient quality or quantity to conclude an individualization does not exist.

Footwear impressions can be of significant evidentiary value in your investigations, but only if you look for them. Obtain training in the collection of these impressions, and if interested, consider learning footwear comparison.

I will end by returning to Paul Kirk’s words: “Physical evidence cannot be wrong, it cannot perjure itself, it cannot be wholly absent. Only human failure to find it, study and understand it, can diminish its value.”

Owen McDonnell retired as the Lieutenant/Supervisor of the Caddo Sheriff’s Office Crime Scene Investigations Division in Shreveport, LA after 31 years. He is the owner of M.O. Forensics LLC and provides consulting and training in crime scene and fingerprint development and comparison techniques, as well as heading workshops through IAI. He holds IAI certifications as a Senior Crime Scene Analyst, Ten Print Fingerprint Examiner and Latent Print Examiner. McDonnell holds a Master of Forensic Science Administration Degree from Oklahoma State University Center for Health Sciences.

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