FAQs
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What kind of results can be expected from the analysis of footwear and tire tracks?
Footwear/tire track examination results are presented in a report that presents the examiner’s observations and conclusions, and may also include supporting details, such as the level of association between the suspect’s shoe or tire and the print or impression from the crime scene.
Forensic footwear and tire track examinations result in one of four possible determinations: an individualization, an elimination, inconclusive results or an association.
• An individualization is when the class, wear and individual characteristics of the collected impression and the known shoe or tire sufficiently match with no unexplainable differences.
• An elimination (exclusion) is when the class, wear and/or individual characteristics do not sufficiently match between the collected impression and the known shoe/tire.
• An inconclusive result occurs when there is not sufficient quality or quantity of information from the questioned impression to reach a meaningful scientific conclusion.
• An association (likelihood) can be drawn when the class, wear and some individual characteristics agree between the collected impression and the known shoe/tire, but are not sufficient to be certain of a match. Results can range from likely to could have, to similar but lacking sufficient detail to be conclusive.
What are the limitations of the analysis?
The analysis essentially requires two things: 1) the print, track or impression evidence, and 2) comparison shoes or tires. The analysis usually depends on the condition of the evidence. If the evidence has been collected properly, and if the substrate (soil, snow, etc.) retains the minute features of the track, a definitive opinion can be reached.
How is quality control and quality assurance performed?
To ensure the most accurate analysis of evidence, the management of forensic laboratories puts in place policies and procedures that govern facilities and equipment, methods and procedures, and analyst qualifications and training. Depending on the state in which it operates, a crime laboratory may be required to achieve accreditation to verify that it meets quality standards. There are two internationally recognized accrediting programs focused on forensic laboratories: The American Society of Crime Laboratory Directors Laboratory Accreditation Board and ANSI-ASQ National Accreditation Board / FQS.
In disciplines such as footwear and tire track examination, where testing requires analysts to compare specific details of two samples, quality control is achieved through technical review and verification of conclusions. This involves an expert or peer who reviews the test data, methodology and results to validate or refute the outcome. The guidelines published by the Scientific Working Group for Shoeprint and Tire Tread Evidence (SWGTREAD) state that all footwear and tire track cases should be technically reviewed and verified by a second independent qualified examiner.
Some of the examinations conducted in this forensic discipline are handled by private contractors. These contractors can identify the quality control and quality assurance steps they employ.
What information does the report include and how are the results interpreted?
The report typically states what was submitted for analysis and the conclusion of the analysis: individualization, elimination (exclusion), inconclusive, or association (likelihood). Some reports from private laboratories include photographs of the examination and conclusion of the results.
Are there any misconceptions or anything else about footwear and tire track examination that might be important to the non-scientist?
While television crime dramas might give the impression that all the evidence at a scene can and will be identified, in practice, many opportunities to collect footwear and tire track evidence can easily go overlooked if the impressions are not readily apparent. Moreover, while shoe prints can be very difficult to protect and can easily be disturbed by first responder traffic at a crime scene, they can often still be located after subjected to some foot traffic.
Another misconception involves tire track examination. On some crime dramas, a detective snaps a photo of a tire track on his cell phone and, using a database or app, instantly retrieves the make/model/number of the tire. In reality, there is currently no automated method for matching tread patterns. The patterns must be meticulously photographed and documented, then compared manually using computer databases and sometimes printed reference books. The process is time consuming and even if the tire can be identified, it is just part of the work needed to connect the tire track to a particular car or individual.