Tool and impression evidence

Photo Credit www.tritechtraining.com

Photo Credit www.tritechtraining.com

The basic theory behind footwear and tire track analysis is that, much like fingerprints, shoes and tires may leave behind either prints (referred to as “imprints”) or impressions that can be examined by investigators. The type of evidence left behind depends largely on the type of surface traveled. For example, a shoe will leave an impression in loose sand, but on a hard surface like concrete or linoleum, it will leave an imprint. These imprints or impressions can be compared to a suspect’s shoe or a vehicle’s tire to determine if the shoe or tire is the same one that left the impression.

As shoes and tires are used, their physical features change over time. This is called wear, and is often reflected in the imprint or pattern left behind. In the case of a tire track, if a vehicle is out of alignment, the right front tire may be heavily worn on the outer edge, leaving a unique wear pattern. A forensic examiner can use that wear pattern along with the tread pattern and information gained from database searches to positively match that impression to the suspect’s vehicle.

During the examination of a crime scene or other location, if footwear or tire track evidence is found and collected, examiners can compare these unknown impressions to known impressions, impressions connected to other crimes and impression evidence stored in law enforcement databases. To do this, examiners use three main characteristics to analyze the imprints and impressions: class, individual and wear.

Class characteristics result from the manufacturing process and are divided into general and limited. General class characteristics include those that are standard for every item of that make and model. Limited characteristics refer to variations that are unique to a certain mold. For example, two tires of the same brand, model and size will have identical tread design and dimensions, but may have slight differences due to imperfections in the molds used during manufacturing.

A tire tread with horizontal bars pointed out with arrows indicating wear.

Enlarged image of a tire tread shows characteristics unique to the mold used to create this tire (red arrows). (Courtesy of John Black, Ron Smith & Associates)

Individual characteristics are unique aspects of a particular shoe or tire that result from use, not the manufacturing process. These could be from damage such as a cut, gouge or crack, or a temporary alteration like a stone or twig stuck in the tread.

Wear characteristics result from the natural erosion of the shoe or tread caused by use. Specific wear characteristics include the wear pattern, the basic position of tread wear; the wear condition, the amount or depth of the wear; and where extreme, the damage to or destruction of the tread. For instance, the location and amount of tread loss on a particular brand and style of shoe will be different for each person wearing the shoe based on how and where they walk, and the length of time they have owned the shoe.

the bottom of a running shoe. The heel is worn down.

(Courtesy of NFSTC)

The FBI compiles and maintains the Footwear and Tire Tread Files database containing manufacturers’ information and information from previously submitted evidence. This information can be used by examiners or investigators to determine the brand name and model of shoe or tire imprints and impressions found at crime scenes. The National Institute of Justice also maintains a list of forensic databases.

 Article reprint from:   http://www.forensicsciencesimplified.org/

The basis for footwear impression evidence is determining the source of a footwear impression recovered from a crime scene. The process of examining footwear impression evidence takes into account class and identifying characteristics. Class characteristics are those characteristics that result from the manufacturing process, such as physical size, design, and mold characteristics. In contrast, identifying characteristics do not result from the manufacturing process, but are accidental, unpredictable characteristics that result from wear. Identifying characteristics include objects that have become attached to the outsole—such as rocks, thumb tacks, or tape—or marks on the outsole caused by cuts, nicks, gouges, and scratches.

In the majority of footwear examinations resulting in an association between a questioned footwear impression and a known shoe, the conclusion most often reached is the correspondence of combined class characteristics such as design and physical size. An association based on class characteristics conveys that the known shoe “could have made” the questioned footwear impression, but another shoe having the same design and physical size also could have made the questioned impression. It should be noted that design and physical size can be used independently to eliminate a shoe as a source of an impression.  


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handbookEverett Baxter Jr.  https://ebjrforensics.com/

Everett Baxter Jr.

Mr. Baxter has over 25 combined years in law enforcement. He began his law enforcement career in 1991 with the Norman Police Department’s EMS Division. This unique service provided EMS care to the citizens of Norman, Oklahoma through the Police Department. At that time, there were only a handful of police agencies that provided EMS services to their citizens and one of three that actually provided ambulance service through the police department. Mr. Baxter joined the Oklahoma City Police Department in 1998 and is currently assigned to the Crime Scene Unit of the Oklahoma City Police Department.

Formal Education

Bachelor of Science (B.S.) in Chemistry, University of Oklahoma, 1991
Associate in Applied Science – Emergency Medical Technology, Okla. City Community College, 1994

Certifications

Crime Scene Investigator (Certificate Number: CI11881)

Professional Experience

Inspector, Investigation Bureau – Oklahoma City Police Department, 1/02/2014 to Present
Adjunct Instructor, Police Science, Oklahoma State University – OKC Campus 8/2005 to 05/2014
Investigator, Investigation Bureau – Oklahoma City Police Department, 1/02/2009 to 01/01/2014
Detective, Investigation Bureau – Oklahoma City Police Department, 1/02/2004 to 01/01/2009
Police Master Sargent, Investigations Bureau, Crime Scene Unit – Oklahoma City Police Department 10/24/2013 to Present
Police Staff Sargent, Investigations Bureau, Crime Scene Unit – Oklahoma City Police Department 10/24/2008 to 10/23/2013
Police Sergeant, Investigations Bureau, Crime Scene Unit – Oklahoma City Police Department, 01/02/2004 to 10/23/2008
Police Sergeant, Operations Bureau – Oklahoma City Police Department, 10/24/2003 to 01/01/2004
Police Officer, Operations Bureau – Oklahoma City Police Department, 01/09/1998 to 10/23/2004
Police Officer, Patrol Division – Norman Police Department, 09/1994 to 01/1998
Police Paramedic, EMS Division – Norman Police Department 08/1991 to 09/1994
Laboratory Assistant, University of Oklahoma Chemistry Department 08/1988 to 08/1991


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About the Author
Darren is a 30 year veteran of law enforcement and criminal investigations. He currently serves as an investigator for the Crawford County Missouri coroner’s office. He holds credentials as an instructor for the Missouri Sheriff’s Training Academy, has served as president of the Missouri Medical Examiners and Coroners Association, and is certified and credentialed in numerous fields of investigation. He holds the position of lead instructor and facilitator for the Coroner Talk™ community as he speaks and writes in the area of death investigation and scene management.

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