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Glass as Forensic Evidence: Purpose, Collection & Preservation

Glass as Forensic Evidence: Purpose, Collection & Preservation
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  • 0:00 Example Scenario
  • 0:33 Glass as Forensic Evidence
  • 1:29 Initial Crime Scene Assessment
  • 2:31 Packaging
  • 3:05 Refractive Index and…
  • 4:20 Lesson Summary
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Lesson Transcript
Instructor: Patricia Jankowski

Patricia is an experienced registered nurse who has worked in various acute care areas as well as in legal nurse consulting. She also has a BSChE.

Broken glass is often found at crime scenes and can be used as forensic evidence. This lesson is about the purpose of collecting glass as forensic evidence, the collection process, and its preservation.

Example Scenario

Imagine a woman calling up the cops, saying: ''Officer, I came home and found my front window smashed. I'm out in the driveway on my cell, and I'm afraid to go into the house! I think someone broke in.''

''Okay, Ma'am, stay where you are. A car is on the way. Don't touch anything.''

A police car pulls up and checks the area for footprints.

''Look, there are large shoe prints in the dirt by the broken window. Dispatch, the perp must be in the area, these footprints are fresh.

Glass as Forensic Evidence

Broken or shattered glass found at a crime scene is an important piece of forensic evidence. The different types of glass that are often found, such as glass from a window, lamp, headlights, or bottles, each have unique properties that can be measured and compared. When glass is shattered by a forceful impact, it scatters for distances up to nine feet or so, and can easily become lodged in a suspect's shoes, clothing, or hair. If a window or glass object is broken or shattered by a projectile, such as a bullet, the breakage pattern can be analyzed to possibly determine the angle of trajectory of the projectile, shedding more light on the crime, such as where the suspect was when the gun was fired.

Using proper collection and preservation techniques when taking samples of glass fragments from a crime scene is crucial in order to avoid altering the evidence or missing important information.

Initial Crime Scene Assessment

Before any samples are taken, the entire scene should be photographed in detail. Tape measures can be used in the photographs to show the distances that the broken glass has traveled. Searching for nearby suspects is of primary importance, as any glass fragments that are retained on their clothing, hair, shoes, or similar will be more likely to fall off as time passes and will probably be gone after about 24 hours.

Samples of glass should be collected from the representative source (i.e., the broken window) and also from fragments of glass that are lying on the ground, floor, or furniture. All samples must be labeled according to where they came from (the original window, a broken fragment on the floor, the inside of the window, the outside, etc.). All the glass fragments should be collected and labeled so that reconstructions can be made if desired. If a suspect is found, samples should be taken from their clothing or hair for comparison. These may be microscopic.

Packaging

All samples should be dry when collected. If fragments are wet, they should be allowed to air dry before being packaged. For small fragments, it is important to use containers that are not too large so that the glass doesn't bounce around and break further. Samples of glass should not be put in glass vials, but cardboard boxes, paper bindles, or envelopes of some kind should be used. These are less likely to alter the sample. Any tape that is used for sample collection should be low-adhesive so it does not adhere to itself.

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