READ: Glass and Soil Evidence

Collection and Preservation of Glass Evidence

Because of the prevalence and usefulness of glass evidence, it is important to properly collect and preserve it for analysis. When glass shatters, it travels in all directions up to four meters away from the site where it shattered! In addition, glass can be transferred to a person, animal or object near the object when it shattered. Anyone who traveled through the area could also pick up a glass particle in a shoe tread, pant cuff, fur or other article. Once it is transferred to a person, object or animal, it can then be transferred much larger distances from the site of the glass shattering. This is why glass analysis is so crucial; if the investigator can state within acceptable limits that a glass fragment from a crime scene matches a glass fragment found on or in the possession of a suspect, it is a good indicator that the suspect was present at the scene. Research has shown that the closer a person or object is to the source of the breaking glass, the more glass particles they are likely to have on them. This idea can be used in cases such as when there is no consensus within a group of suspects on who actually broke a glass window in a burglary. The person found with more glass on them is most likely the person that broke the window! In the case of glass particles transferring to clothing, there are a few things to keep in mind:

• Particles are less likely to transfer and stay on slick clothing such as Nylon.

• Particles are more likely to transfer and stay on rougher textured clothing such as woven sweaters of wool.

• Time matters; glass particles tend to fall off over time. Larger pieces will fall off before smaller pieces; thus examining clothing for glass evidence should be done as soon as possible.

• Glass tends to stick to wet clothing longer than dry clothing.

• Glass falls off clothing faster if the person is running or more active.

Glass Collection

Glass evidence should be collected from the scene and packaged to prevent any further breakage. The direction of impact should be determined and the orientation of the glass (inside/outside) should be noted when collected.

 Here are the basic glass collection procedures:

• Collect as many of the glass particles that you can near an obvious broken glass object. In windows, collect broken glass pieces from the window itself so that the identity of the glass source is ensured.

• If there is glass from multiple sources in a crime scene, make sure to package them in separate boxes so that they don't get mixed together.

• All packages of glass evidence should be labeled with the location and description of the glass source (if known).

• Large pieces of glass should be packaged in sturdy cardboard boxes. Small pieces of glass fragments can be packaged in envelopes or bags as indicated.

• Ensure the package has no holes through which glass evidence could fall out. Secure corners of boxes with tape.

• Collect clothing items suspected to have glass evidence on them and packaged them whole to send to the lab for examination. It is important that the clothing isn't shaken or handled excessively to avoid dropping small glass particles.

• When collecting glass evidence from hair: Comb the hair over a large clean piece of paper, such as butcher paper so that the glass particles are captured on the surface of the paper. Fold and tape the paper so that the glass pieces are securely held inside the paper bundle.

• If an object is too large to collect (such as carpet), the area can be vacuumed and the contents of the vacuum cylinder can be submitted to the lab.

Georgia Virtual, Forensic Properties of Glass and Soil Evidence, CC BY-NC-SA 3.0