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Pattern Marks : What Can They Tell Us?

What Is Pattern Mark?  

In everything that we do, we will definitely leave a mark wherever we go. A car will leave tire tracks, the shoes on our feet will leave footwear prints, and even the screwdriver used to take the paint’s lid off will leave its mark. The simple principle that Edmund Locard had proposed was ‘every contact leaves a trace’ and most appropriately applied in the field of marks and impressions, where when two items are put together, they will tend to leave a mark on one another.

Types Of Pattern Mark 

Impression evidence involves the interaction of two or more surfaces or objects in a manner that either leaves a mark on the other or removes a portion of the surface of one or both. Impressions are formed by the contact and retention of characteristics from each of these objects.

Common types of pattern mark include (but not limited to) footwear impression, tire impression and toolmark.

Footwear Impression  

Footwear impressions are often discovered at the scene of the crime. This evidence can provide investigators with certain information that can assist them in locating a suspect.

Most footwear evidence, when collected and preserved properly, can provide the type of footwear, manufacturer, approximate size, number of suspects, path through and away from the crime scene, involvement of the evidence, and events that occurred during the commission of the crime.

Footwear evidence can be found in two forms that are impressions and prints. The impression is normally described as a three-dimensional impression, such as an impression in mud or a soft material, while the print may be made on a hard surface by dust, powder, or similar medium.

 
Figure 1 and 2 : Example of footwear impressions found in a scene of crime
(Source:forensicmindslcc.yolasite.com)

Tire Impression           

Tire impressions are a significant source of evidence, dictating who went to and from the crime scene. When tires are received for comparison, test impressions are normally made to aid the analyst. As in the case of footwear impressions, when individual detail is present between the known tires and the impressions received from the scene, it is possible to individualize an impression to a specific tire.

In the examination of tyre impressions, the analyst will note:

  1. Manufacturer’s Design.
  2. Size.
  3. Wear Patterns.
  4. Any Individual Characteristics Present.
  5. Arrangement of the Tires on the Suspect’s Vehicle.
  6. Arrangement of Tires Established at the Crime Scene.
  7. Number of Grooves.
  8. Tread Design.
  9. Other Individualizing Characteristics.

Tire impressions found at the crime scene can be submitted as plaster casts, photographs, electrostatic lifts, or as impressions on paper or cardboard.

Figure 3 : Tire impressions at outdoor scene and Figure 4 : Tire prints found at scene (Source:www.forensicsciencesimplified.org)

Toolmark

Toolmark evidence is most commonly found in cases of breaking and entering, theft, assault, and homicide. The goal of toolmark analysis is to determine if a particular tool produced a particular mark. Due to manufacturing processes and wear from prolong usage, tools can bear unique microscopic characteristics, allowing their toolmarks to be positively identified as originating from that specific tool used.

Common Tools that are Used:

  1. Bolt Cutters.
  2. Pry Bars.
  3. Screwdrivers.
  4. Drill Bits.
  5. Hammers.
  6. Knives.

Common Evidence Received:

  1. Pliers/Channel Locks.
  2. Safes.
  3. Window Sills.
  4. Door Frames.
  5. Door Knobs.
  6. Tires.


Figure 5 : Example of a toolmark impression
(Source : www.maine.gov)

Pattern Mark on Body

Pattern print on an individual’s skin may be seen as bruising.


Figure 6 : Example of pattern mark on human body
(Source : www.deviantart.com)

Pattern Mark on Scene

Items of footwear and their impressions that remain at the crime scene offer sound, reliable, and demonstrative evidence of a person’s presence in that particular area. Both macro and micro casting techniques are utilized for comparisons of shoeprints, tireprints and other impressions. In addition to casting techniques, impressions can be lifted from a variety of surfaces. Techniques include gel lifts or utilization of the laboratory’s electrostatic lifting device. These lifts can then be compared to impressions of known footwear prepared in the laboratory.

How The Pattern Marks Lead to The Investigation       

Comparisons of shoeprint and tire tread impression evidence with submitted shoes or tires are also conducted. Impression evidence can be in the form of photographs, lifts, casts, or an original item bearing an impression. A shoe can be definitively identified with an impression if there is sufficient detail in the impression and sufficient identifying characteristics are on the shoe. A tyre can be positively identified with an impression if the same criteria are met.

Shoes are fascinating items of clothing. They are made in a variety of ways and in thousands of designs. In turn, each design is made in many distinguishable sizes. As the outsole wears, their design and other characteristics steadily change. They acquire cuts, scratches, nicks, and other characteristics of a random nature. These traits serve to give them a tremendous degree of individuality. As they track through soil, snow, sand, residue, and other materials, supporting the weight of their wearer, they impress their distinct and individual features on or into the surfaces over which they pass.

In order to compare the tool submitted from the suspect with the known mark from the evidence, test impressions need to be made in a similar material. Usually, soft lead is used for comparison purposes. The test impression and the known mark are compared side by side on a comparison microscope to determine if there are any individualizing characteristics that could link the two marks. Two types of marks that are identified in toolmark examination are striations and impressions. Striations are formed by the sliding or scraping of one material over another, while impressions are compression or impact marks.

How Acceptive Can Pattern Mark Evidence be in The Court of Law     

Many attorneys have sought to have the examiner’s testimony omitted from cases claiming the examinations of pattern mark evidence are not rooted solidly in science or that the examiner’s conclusions are subjective and cannot be trusted. A scientific foundation and objectivity are found in any experienced toolmark examiner’s toolmark comparisons. In recent years, to reinforce these ideas, different groups have sought to make objective toolmark comparisons with the use of comparative statistical algorithms.

References                 

  1. Lecture notes for Forensic Evidence and The Aspects of Law. MSc Forensic Science. Universiti Teknologi Malaysia. 2010.
Last Reviewed : 19 May 2015
Writer : Salina bt. Hisham
Accreditor : Khoo Lay See

 

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