Physical evidence must be collected and preserved carefully to avoid contamination or damage. The collection process involves documenting the location of the evidence, using proper equipment to gather it, and packaging it securely. Preservation involves storing the evidence in a controlled environment to prevent degradation or destruction. This often requires specialized equipment such as refrigeration units or humidity-controlled storage facilities. Proper collection and preservation of physical evidence are critical to maintaining its integrity and ensuring that it can be used effectively in criminal investigations.