When evidence could degrade, it is important to take steps to preserve it. Here are some guidelines for handling and preserving evidence:

• Collect fragile evidence first: Ideally, an investigator should carefully collect the most fragile evidence first, before disturbing the scene by removing larger, heavier, or less fragile items.

• Air dry wet items: Wet items should be air-dried or placed in a breathable packaging to prevent molding.

• Use paper containers: Most evidence should be placed into paper containers, such as bags and envelopes. Evidence packaged in plastic bags may be exposed to moisture, hastening deterioration and risking environmental contamination, such as mold, and the destruction of useable DNA or other trace evidence. Investigators should not package moist evidence until it is thoroughly dry and or seal collection bags or envelopes prematurely.

• Store evidence properly: Most evidence should be stored at room temperature, unless it is liquid evidence, in which case it should be refrigerated and packaged in a sterile glass or plastic bottle. An investigator is responsible for appropriately labeling all evidence collection containers with the case number, collection date, and the initials of the collector.

• Prevent contamination: Those responsible for collecting evidence must understand and employ a variety of evidence preservation protocols, depending on the type of evidence. Some guidelines apply to all evidence, such as limitations on the number of individuals allowed to handle the evidence, use of safeguards to minimize contamination, proper collection documentation, acceptable chain-of-evidence documentation, and evidence appropriate storage.

• Repair damaged evidence: Forensic samples that have been damaged or purposefully destroyed must be repaired for analysis and use in court. Several methods exist that can repair this.

• Handle biological evidence with care: Degradation of biological evidence is most commonly caused by exposure to moisture and heat, which encourages the growth of bacteria. This can lead to the destruction of the DNA and the possibility of incomplete or no DNA typing results being obtained. Contamination of samples, either by coming into contact with each other or with DNA from a person handling the sample, can lead to uninterpretable DNA results. To avoid contamination of DNA evidence, it is recommended to always wear latex gloves when handling biological evidence, change gloves between the handling of each item of evidence, process biological evidence on a clean area, and be careful not to talk excessively over biological evidence. To avoid the degradation of DNA evidence, it is recommended not to expose biological evidence to excessive heat or humidity, allow biological evidence to air-dry prior to packaging, and store biological evidence in a cool, dry place.