Best Practices for Collecting and Preserving Wet Evidence

Wet evidence (e.g. blood-soaked fabrics, bodily fluids, plant material) is highly vulnerable to degradation and contamination. Forensic protocols require careful handling to preserve such evidence for analysis. Investigators should immediately don fresh gloves and avoid direct contact or blowing on evidence. Each wet item should be documented (location, date, collector) and placed in a temporary container for transport. Whenever possible, limit the evidence’s contact with plastic or impervious containers until drying can occur, since plastic traps moisture and promotes mold. Transport wet items (especially biohazardous ones) in sealed leakproof containers with biohazard labeling. For example, swabs of suspected biological fluids should be air-dried and then heat-sealed in plastic bags, and any liquid (e.g. from a syringe) should be transferred to a screw-top vial (never in plastic bags). Proper initial handling means wearing new gloves for each item and immediately starting a written chain-of-custody – every handler must sign and date evidence transfers.

Drying and Decontamination

All wet evidence must be dried thoroughly before long-term storage. Air drying at room temperature in a controlled area is preferred. Set up a dedicated drying space (e.g. locker, shower stall, or drying cabinet) away from direct sunlight, with surfaces that can be cleaned. Place evidence on clean hangers or racks with absorbent paper beneath to catch drips, and change the paper (and decontaminate) between items to prevent cross-contamination. Hang each garment with fresh paper layers between different items. All items from different cases or individuals should be dried separately. If no specialized equipment is available, simple methods work: use a temperature-controlled room with good air circulation, change gloves before handling each item, and spray surfaces with bleach or alcohol before and after each use. In some protocols, investigators may freeze evidence that cannot be immediately dried. For example, Connecticut guidelines require that “all items are to be air-dried prior to packaging; if unable to air dry, freeze any items containing biological materials and submit … as soon as possible”. (Note: long-term freezing applies to items like blood or urine which cannot be dried; dried biological swabs and stains typically do not require refrigeration.) In all cases, avoid plastic for long-term storage of biological evidence – use plastic only as a short-term measure while transporting to the drying area.

Drying Checklist:

• Air-dry evidence at room temperature in a clean, secure area.

• Use paper or kraft paper around wet items (paper-lined hangers, racks).

• Decontaminate drying area between items; consider 10% bleach or 70% alcohol wipes.

• Separate items by case/person when drying to prevent mixing DNA.

• After drying, package evidence immediately; do not leave damp material unprotected (risk of mold).

Packaging and Storage of Dried Evidence

Once evidence is thoroughly dry, select appropriate containers. Breathable packaging (paper bags or boxes) is recommended for most biological or moisture-sensitive items. Paper allows any residual moisture to escape and prevents condensation. Plastic (zip-lock) bags or bottles are acceptable only for non-biological items or as temporary packaging; for example, drugs in powder form or small hardware may be placed in heat-sealed plastic bags. However, never long-term store damp biological items in plastic, as this traps moisture and fosters degradation. If an item must remain wet (e.g. blood in a syringe), follow agency procedures (often immediate refrigeration or freezing) until transfer to the lab.

• Labeling: Every container must be clearly labeled with case number, item description, location/date collected, and collector’s identity. Include biohazard markings on fluid-containing packages.

• Sealing: Containers should be sealed so that any opening attempt is obvious. This can be done with tamper-evident evidence tape or sealed bag flaps. For instance, Kansas guidelines note that “items of evidence submitted… must be properly sealed… Seals may be made using tamper-indicating evidence tape, heat sealing of plastic bags, or tamper resistant adhesive seals”. After sealing, the investigator’s initials (and date) should be signed across the seal onto the container to bind the seal to the package.

• Absorbents: If any moisture remains or liquids are present, include absorbent material (e.g. cotton, gauze) inside the container to prevent sloshing. Label such evidence as biohazardous.

• Secondary Containers: Place small packages into larger containers (boxes or tubs) as needed. Seal the outer container with tape and initial it as well. When mailing or transporting, place paperwork (evidence log or submission form) within the sealed container, not taped on the outside, to avoid interfering with evidence seals.

 Figure: A crime scene technician seals a paper evidence bag with tamper-evident tape. Sealing containers visibly ties the contents to their chain-of-custody record. Tamper-evident sealing is explicitly required by standards – for example, an OSAC/NIST draft standard states that “upon collection, evidence shall be sealed in a manner that maintains evidence integrity by preventing… tampering”. Similarly, forensic submission protocols mandate that each submitted item be closed so that opening it would cause obvious damage, and that all seals bear the handler’s initials.

Maintaining Chain of Custody

Every transfer or handling of evidence must be documented to establish an unbroken chain of custody. Upon collection, complete an evidence log or custody form noting the time, location, and conditions of collection. Each item’s container should be tagged with a unique evidence number and signed by the collector. Whenever evidence changes hands (e.g. crime scene technician to property custodian, to analyst), record the date/time and the names/signatures of persons relinquishing and receiving custody. Many agencies use tamper-evident security bags that include a printed chain-of-custody form or barcode for convenience.

Good chain-of-custody practice ensures legal admissibility. As NIJ guidance explains, “each person who handles the item should make a log entry… As the item passes from person to person… a chain of receipts should be created. No question should ever exist at trial… that concerns missing items, mishandling or… breaks in the chain of custody”. Evidence storage areas must be secured with limited access, and evidence remains in its sealed packaging until analysis. Use pre-numbered bags and continuously track each seal: in practice, many tamper-evident bags have serial numbers on both bag and receipt stub to match evidence bags to their documentation.

Tamper-Evident Security Bags

Tamper-evident security bags are specialized evidence containers engineered to make unauthorized opening immediately obvious. These bags have a secure adhesive flap that, when lifted, leaves a bold “VOID” or similar pattern on the bag surface. They often include sequential barcodes, printed chain-of-custody fields, and tear-off receipt tabs. The combination of features deters tampering and provides a clear audit trail. For example, one manufacturer notes that its tamper-proof evidence bag has “multiple layers of tamper proof seals to prevent unauthorized access,” with a sequential barcode that ensures the bag “can be tracked and traced throughout the entire journey, thereby maintaining compliance with the chain of custody”. In law enforcement applications, these security bags are explicitly designed for evidence – as one supplier explains, the “tamper proof evidence bag with audit traces ensures the integrity of forensic evidence”.

Using TESBs strengthens admissibility by providing visual proof of any breach. If a bag is reopened, the “VOID” message is permanently displayed, alerting examiners and the court to potential tampering. Guidelines reflect this: an OSAC standard requires that long-term evidence packaging “include tamper detection ability”, such as signed tape or equivalent. By contrast, a plain zip-top bag can be opened and resealed without obvious evidence. Modern TESBs eliminate this risk. They also improve accountability: many have write-on panels for case numbers, evidentiary descriptions, and space for initials. As one packaging expert notes, tamper-evident tapes and bags “act as a visual deterrent” and “provide a tamper alert… for businesses and individuals alike,” simplifying audits and strengthening legal chain-of-custody records.

Common Mistakes to Avoid

• Packaging damp items in plastic:  This is perhaps the most frequent error. Trapping moisture in a plastic bag will quickly cause mold growth, which can destroy DNA or other biological evidence. Always dry items first or use breathable packaging.

• Failure to dry thoroughly:  Packing wet evidence (e.g. clothing, napkins) before it’s fully dry will lead to contamination and loss. Never skip the drying step. If an item cannot be dried on-scene, treat it as biohazard and freeze or refrigerate until processing.

• Cross-contamination between items:  Reusing gloves or drying multiple items from different cases together can transfer DNA. Always change gloves between evidence items and keep cases separate during drying and packaging.

• Improper sealing:  Failing to fully seal evidence or neglecting to initial seals jeopardizes integrity. For example, using staples without covering them with tape, or not marking the seal to break over the package boundary, can allow undetected access.

• Incomplete documentation:  Omitting signatures, times, or item descriptions at any transfer breaks the chain of custody. Keep meticulous logs and attach all required forms. As one expert warns, chain-of-custody lapses “should never occur at trial,” since they “might jeopardize evidence admissibility”.

By rigorously following these procedures – drying wet evidence appropriately, using the right packaging, and sealing items with tamper-evident methods – forensic professionals preserve the probative value of evidence. Tamper-Evident Security Bags are a valuable tool in this process, supporting robust chain-of-custody and helping to ensure that evidence stands up under legal scrutiny.