Glass

Detailed Procedure:

When collecting a known comparison sample, take samples directly from the source of broken glass, if possible. Take comparison samples from the ground only when there is no glass remaining at the source. Select a comparison sample from each possible source (ie: different window panes). Collect a comparison sample no smaller than a quarter and no larger than a sheet of paper. Package samples separately from one another as described below, labeling them appropriately.

Glass fragments may contain fingerprints and therefore should be handled as little as possible and with gloved hands, handling the edges of the glass if possible.

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To collect glass fragments:

1. Photograph the fragments in place.

2. Wear eye protection and new, unused, clean latex or nitrile gloves. Use protective gloves (properly cleaned or new) if necessary to prevent cuts from the glass.

3. If the glass is being processed for latent prints, dust fragments for latent prints or preserve for latent prints. If any prints are observed, photograph the prints. These pieces of glass should be packaged in a sturdy container. Be sure to secure the piece of glass so that it doesn't move in the container and rub the latent prints off the surface. DO NOT cushion the glass with packing materials, such as balled up paper or packing peanuts.

4. If the glass is being submitted for glass comparison, be sure to take glass from each of the broken objects. The known glass samples should be placed in a sturdy container so that they do not cut through the packing material.

5. If the glass is being submitted to determine the direction of force, bullet impact, or fracture analysis, do not remove glass fragments from the frame. Instead, collect the entire frame. If necessary, use masking tape to keep glass from falling out of the frame. Submit as much broken glass from the surrounding area as possible so the reconstruction can be as complete as possible. If necessary, mark the glass surface with tape to identify the location where the fragments were found (inside or outside the structure) and/or which side was facing out.

6. Package any questioned pieces of glass separately from known pieces.

7. Seal the container with evidence tape, and initial and date the tape.

8. Label the container with identifying information, including case number, date, exhibit number, a brief description, and your name.

9. Store the item in a secure location, such as a locked evidence van or your vehicle, until you are able to transport it to the laboratory.

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If the glass will also be examined for ignitable liquid residue (for example, if it is part of a Molotov cocktail), please consult the laboratory for the proper collection procedure. Items should not be air-dried or packaged in an air-permeable container if they will be examined for ignitable liquid residue.

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Laboratory testing of glass fragments:

Fracture matching may be possible. Comparison of elemental and optical qualities of glass between known and questioned samples can be done to determine if they could have originated from the same source.

Glass window panes can be reconstructed in an attempt to determine the direction of force applied to cause the break or the order in which consecutive breaks were made (ie: which break was made first).