A Guide to Evidence Management
Tips & Best Practices for Biological Evidence Storage
Biological evidence is extremely effective in identifying suspects and solving crimes. A study by the National Institute of Justice found that even DNA evidence collected at property crime scenes (non-violent cases) yielded impressive results:
- Twice as many suspects were identified and arrested.
- More than twice as many cases were accepted for prosecution.
- DNA evidence identified twice as many suspects and produced 3 times the arrests over fingerprint evidence.
With DNA evidence from property crime scenes yielding such encouraging results, it makes sense to more routinely collect, analyze, and preserve biological evidence.
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Establish & Maintain Proper Preservation Conditions
Biological evidence storage can be a challenge. These types of evidence must often be kept for decades, so it’s essential to establish and maintain proper preservation conditions to preserve the integrity of evidence over the years. Different types of evidence require different storage conditions, but temperature is usually one of the primary concerns. Biological evidence also needs to be protected from moisture, sunlight, and excessive heat. Last but not least, evidence must be kept secure to preserve the chain of custody and maintain admissibility in court.
Here are some general guidelines on recommended conditions and equipment for securing and preserving biological evidence in storage. Be sure to check with your crime lab for official recommendations and protocols governing short-term evidence storage and long-term evidence storage for DNA and other biological evidence in your jurisdiction.
Temporary storage equipment for biological evidence.
Some departments use residential refrigerators or small under-the-counter refrigerators to temporarily store biological evidence. Using consumer-grade refrigerators and freezers presents 3 major concerns:
- Maintaining Chain of Custody
Consumer-grade refrigerators are difficult to lock down, meaning the integrity of evidence can be questioned at trial. - Temperature Variations
Temperature fluctuations and freeze-thaw sequences cause biological evidence to degrade. - Cross-Contamination
If not separated by physical barriers, evidence from one container could contaminate another.
These concerns can all be avoided with refrigerated evidence lockers, which are specifically designed for law enforcement.
Many police departments have refrigerated compartments installed along with other temporary evidence lockers. Professionally designed refrigerated evidence lockers maintain a steady temperature and the compartments lock securely to ensure the integrity of evidence. In addition, each compartment is fully sealed to prevent cross-contamination.
Best Temperature Conditions for Short-Term Biological Evidence Storage
This chart is intended as guidance. When in doubt, defer to your crime laboratory’s policy.
| Bones | Acceptable | Acceptable | Acceptable | |
| Buccal Swabs | Best | Less than 24 hours | ||
| Dry Biological Stained Item | Best | Acceptable | ||
| Feces | Best | |||
| Hair | Best | Acceptable | ||
| Liquid Blood | Never | Best | Less than 24 hours | |
| Swabs with Biological Material | Best (wet) | Best (dried) | ||
| Urine | Best | Less than 24 hours | ||
| Vaginal Smears | Best | |||
| Wet Bloody. Items (if cannot be dried) | Best | Acceptable | Less than 24 hours |
Source: The Biological Evidence Preservation Handbook, page 18. Frozen: temperature is maintained thermostatically at or below –10 °C (14 °F). Refrigerated: temperature is maintained thermostatically between 2 °C and 8 °C (36 °F and 46 °F) with less than 25 % humidity. Temperature controlled: temperature is maintained thermostatically between 15.5 °C and 24 °C (60 °F to 75 °F) with less than 60 % humidity Room temperature: temperature is equal to the ambient temperature of its surroundings; storage area may lack temperature and humidity control methods.
Long-Term Storage Equipment for Biological Evidence
Evidence is typically transferred into long-term storage after analysis is concluded. In some states or jurisdictions, biological evidence can be sent to an off-site storage facility for long-term preservation. In many jurisdictions, however, biological evidence must be preserved on site.
Many police departments have refrigerated compartments installed along with other temporary evidence lockers. Professionally designed refrigerated evidence lockers maintain a steady temperature and the compartments lock securely to ensure the integrity of evidence. In addition, each compartment is fully sealed to prevent cross-contamination.
Evidence must be stored in a way that meets these goals for years, or even decades:
- Evidence is secure (chain of custody is maintained)
- The structural integrity of the evidence is preserved
- Evidence can be retrieved and identified
- Staff safety is maintained
Departments that need to store a large quantity of biological evidence can opt for walk-in coolers and/or freezers. They save on cooling expenses by using high-density storage systems, which help in 2 ways:
They can store more in less space, which reduces the size of the cooler or freezer.
The system fills the cooler or freezer, allowing it to operate more efficiently.
Best Temperature Conditions for Long-Term Biological Evidence Storage
This chart is intended as guidance. When in doubt, defer to your crime laboratory’s policy.
| Bones | Best | |||
| Buccal Swabs | Best | |||
| DNA Extracts | Best (liquid) | Acceptable (liquid) | Acceptable (dried) | |
| Dry Biological Stained Item | Best | |||
| Feces | Best | |||
| Hair | Best | Acceptable | ||
| Liquid Blood | Never | Best | ||
| Swabs with Biological Material | Best (dried) | |||
| Urine | Best | |||
| Vaginal Smears | Best |
Source: The Biological Evidence Preservation Handbook, page 19. Frozen: temperature is maintained thermostatically at or below –10 °C (14 °F). Refrigerated: temperature is maintained thermostatically between 2 °C and 8 °C (36 °F and 46 °F) with less than 25 % humidity. Temperature controlled: temperature is maintained thermostatically between 15.5 °C and 24 °C (60 °F to 75 °F) with less than 60 % humidity Room temperature: temperature is equal to the ambient temperature of its surroundings; storage area may lack temperature and humidity control methods..
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