Collecting evidence at a crime scene is an essential part of crime investigation. Proper procedures must be followed, and crime scene technicians must ensure they have gathered all relevant pieces of evidence. This is particularly challenging with glass --- a broken headlight, window or light bulb may have shattered into many pieces over a wide area at a crime scene. The technician must collect each piece individually and tag and document it for later analysis. Large pieces can be collected by hand and sometimes can be pieced back together in the lab; smaller pieces must be picked up with tweezers.
Draw a detailed schematic of where the glass is located in relation to the crime scene. Mark each piece of glass with a numbered evidence flag or cone. Photograph the scene with markers in place.
Put on latex gloves; wear gloves throughout evidence collection process to avoid contaminating the evidence. Collect and label at least one reference piece of glass to be used for later comparison with shards found on a suspect or clothing. Pick up large pieces of glass by hand. Place each piece into a separate carefully marked evidence bag or envelope. If the pieces are large enough to later be fit back together in the crime lab, group bags together to keep them from being separated during transporation back to the lab.
Use adhesive tape or tweezers to pick up small glass shards or pieces. Place each piece into carefully marked evidence bags or envelopes. Tweezers may scratch or damage shards, so they must be used with caution. Glass embedded in clothing, seat covers or other fabric should not be removed; instead, carefully wrap the entire item to avoid dislodging the glass and place it in a labelled evidence bag.
Log each piece of glass collected into the evidence log sheets or log book so each piece is readily identifiable during later analysis in terms of exactly where it was found at the crime scene. Package each piece so it does not break or rattle around in the collection container; avoid damaging the edges of the glass pieces since this might hinder later efforts to piece a broken object back together.
Ensure official chain of custody is maintained during transport between the crime scene and the crime investigation laboratory to protect its integrity for use as evidence in any future criminal proceedings.
Proper documentation is essential to ensure each piece of glass evidence collected is accounted for and can be used later for forensic analysis and in criminal or judicial proceedings. Failure to correctly document and handle crime scene evidence may result in its being ruled inadmissable for use in court.
Do not put multiple pieces of glass, even when from the same broken source, in the same evidence collection containers. Each piece must be processed individually. Dry off any item containing moisture (blood, body fluids), since packing up damp items can cause damage to the evidence.