COUNTY OF SANTA CLARA OFFICE OF THE DISTRICT ATTORNEY CRIME LABORATORY PHYSICAL EVIDENCE MANUAL GEORGE KENNEDY DISTRICT ATTORNEY EVIDENCE

A. Biological Evidence Collection - General Guidelines

1. Wear gloves at all times.

a. Prevents contamination of evidence by individual and vice versa.

b. Change gloves as they are soiled to prevent cross-contamination of evidence items.

2. Do not cough or sneeze on evidence items.

3. Always clean utensils after collection of each sample to prevent cross-contamination.

4. Always collect control samples.

Purpose of control samples is to demonstrate that the background of the substrate (what item the stain is on) does not produce a positive result for the particular lab test.

a. Controls are collected as close as possible to the stain area without contaminating it with the stain

b. Always document where the control is taken from. Include distance from stain.

B. Handling and Storage of Biological Evidence

1. Each item collected (stains and controls) must be:

a. Air-dried

Do not heat stained material or place it in sunlight to dry. Hand clothing and similar articles in a room with adequate ventilation.

b. Packaged separately in paper (i.e., bindles, envelopes, paper bags, boxes)

Do no use plastic bags, plastic containers, glass bottles/vials, or any other non-porous packaging material.

c. Stored frozen

Consider special handling of non-absorbent items, such as metal or plastic. Condensation from thawing could disturb or destroy biological evidence, particularly bloody fingerprints. Such items should be kept at room temperature and submitted to the Laboratory as soon as possible.

2. Liquids (generally reference samples)

a. Blood

Reference bloods samples, collected in yellow stoppered (ACD) vacutainer tubes, are refrigerated. DO NOT FREEZE. Submit to the Laboratory as soon as possible.

b. Saliva

Collect saliva on a sterile gauze pad, air dry and package in paper. Do no package in non-porous packaging material (i.e., plastic bags/containers, glass bottles/vials, etc.).

C. Dried Biological Stain Collection

1. If possible, collect entire item and submit to the Laboratory (i.e., knives, clothing, bedding, etc.). Package each item separately in a paper container. Controls do not need to be collected.

2. For larger items, cut out stain such that it includes an unstained portion for use as a control (i.e., mattress, sofa, car seats, walls, floors, carpet, etc.). Package each item separately in a paper container.

3. Swab stain area with sterile cotton swab slightly moistened with distilled water. Concentrate on stain. Control samples are collected in the same manner from a nearby unstained area. Air-dry and package each item separately in a paper container.

D. Wet Biological Stain Collection

1. Wet biological stains (i.e., blood pools, semen, saliva) should be collected on a sterile gauze pad or sterile cotton swabs and allowed to air dry. Package each item separately in a paper container. Do not use non-porous packaging material (i.e., plastic bags/containers, glass bottles/vials, etc.).

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