Preserving biological evidence is crucial for accurate analysis and reliable results in forensic investigations. Proper preservation techniques prevent degradation, contamination, and loss of the evidence's integrity. Long-term storage, defined as anything exceeding 72 hours, requires specific temperature and humidity controls.
Here's a breakdown of how to preserve biological evidence:
1. Immediate Actions & Documentation:
- Proper Collection: Use sterile equipment and appropriate collection techniques to avoid contamination.
- Thorough Documentation: Meticulously document the collection process, including the date, time, location, and description of the evidence. Photographing the evidence in situ is also vital.
- Chain of Custody: Establish and maintain a strict chain of custody to track the evidence from collection to analysis, ensuring accountability at every step.
2. General Preservation Techniques:
- Drying: Allowing evidence to air dry can prevent microbial growth. This is especially applicable to items like clothing or bedding that may contain biological fluids.
- Refrigeration: Cooling evidence slows down enzymatic activity and microbial degradation.
- Freezing: Freezing is ideal for long-term storage, as it effectively halts biological processes.
3. Specific Preservation Guidelines Based on Evidence Type:
The specific method used depends on the type of biological evidence collected:
| Evidence Type | Preservation Method | Temperature/Humidity Guidelines |
|---|---|---|
| Blood/Bodily Fluids | Air dry completely before packaging in a breathable container (e.g., paper bag or envelope). Alternatively, freeze. | Refrigerate (2°C to 8°C) or Freeze (below -10°C) |
| Hair/Fibers | Store in a clean, dry, and sealed container (e.g., paper envelope or vial) at room temperature. | Maintain low humidity (less than 25% if possible) |
| Semen | Air dry stains thoroughly. Freeze liquid semen samples. | Refrigerate (2°C to 8°C) or Freeze (below -10°C) |
| Tissue/Organs | Formalin fixation for histological examination. Freeze if DNA analysis is planned. | Refrigerate (2°C to 8°C) or Freeze (below -10°C) |
| Bone/Teeth | Clean and dry thoroughly before storage in a clean container. | Room temperature, low humidity |
4. Storage Conditions:
- Short-Term Storage (less than 72 hours): Refrigeration (2°C to 8°C / 36°F to 46°F) is generally suitable.
- Long-Term Storage (more than 72 hours): Freezing at or below -10°C (14°F) is recommended.
5. Packaging Considerations:
- Breathable Containers: Use paper bags, envelopes, or cardboard boxes for items that need to dry to prevent mold growth.
- Sealed Containers: Use airtight containers for frozen samples or items that must be protected from contamination.
- Tamper-Evident Seals: Use tamper-evident seals to ensure the integrity of the evidence and prevent unauthorized access.
6. Preventing Contamination:
- Wear gloves and protective clothing.
- Use disposable or sterilized equipment.
- Avoid talking, sneezing, or coughing over the evidence.
- Process each item of evidence separately.
- Control access to the storage area.
In summary, proper preservation of biological evidence requires meticulous attention to detail, appropriate storage conditions, and adherence to strict protocols to maintain its integrity for accurate analysis and reliable legal proceedings.
