Preserving and maintaining evidence collected at a scene is crucial. The key is understanding evidence and understanding the proper way to package it.

First, a few important points: Choose packaging of the proper size and material for the evidence. Package each piece of evidence separately, and properly label, seal, and document it. Evidence tape is designed to fracture easily to indicate tampering; it’s not meant to hold bags shut and boxes together. Use packing tape to seal bags and boxes, then place evidence tape over the packing tape. Sign across the tape, with half the signature on the tape and half on the package. That way, your evidence will be securely packaged, and you’ll notice any tampering.

For basic collection, you’ll need an assortment of clean, new paper and Ziploc bags. Never use an old paper sack or an old plastic bag, or you risk contaminating your evidence. If you put a sweater from the scene into an old grocery bag and the lab finds a hair, they won’t know if it came from the bag or the sweater.

Use Ziploc bags for items, such as nuts and bolts, that won’t be processed further. Keep different sized bags on hand, since you want to match the item to the bag.

Paper should be used for items that need to breathe. Fingerprint evidence, pillows, comforters, etc. go in paper. Wet items go into paper. If you seal a bloody shirt in a Ziploc, it will putrefy and be ruined. Put bloody clothing into paper bags and transport to your station. While it’s drying, place white paper bags under the clothing to collect any trace evidence that falls. Retain the transport bag and white paper bags as evidence. Green marijuana also needs to go in a paper bag; if sealed in plastic, it will mold and won’t test properly.

Package small items carefully or they could be lost. If you have a single fingerprint on a flap lifter, attach it to an evidence sheet, and then package it in a 5 inch x 7 inch manila envelope. Use trace evidence lifters to process clothing, furniture, and similar items. Put the protective sheet over the adhesive, then tape it shut to keep the evidence in place. If you find a piece of hair or other loose evidence, collect it with tweezers and place it in clean pharmaceutical paper. Put both in a glassine envelope, fold it, and seal it shut. Again, place these small items in larger envelopes, seal, and label

Electronic items require special attention. Cell phones can be activated and deleted from remote sites, which could destroy valuable information. Place cell phones in special bags that block signals and protect from static electricity. These bags can also be used with computer components. If you’re going after computer equipment, bring an expert. Otherwise, you could shut off a computer and discover it was set to automatically delete data. After the expert checks it, then put the hard drive and other sensitive components in protective bags. Any parts that are too large to be packaged need to be documented with a property tag or label.

At some scenes you’ll have DNA evidence. If you use swabs on blood, semen, saliva, or urine stains, let them air dry at the scene. When they’re dry, pack each in a separate swab box or put each in a separate coin envelope.

Some items may present challenges because they pose a safety risk. Secure this evidence while also protecting yourself and others. Package large, oddly shaped items like machetes in cardboard tubes designed for posters. Place other sharp objects like syringes and glass fragments in specially designed plastic collection tubes. Knives can go into these plastic tubes or into specially designed knife boxes. A knife box allows you to strap the weapon in without damaging the evidence. If any of these items contain blood, other body fluids, tissue, etc., you must mark the outside of the package with a biohazard label.

When dealing with firearms, first make sure that the weapon is unloaded, cleared, and safe. Then pack the firearm in a box specially designed to hold weapons in place. The outside package label must indicate that the weapon has been cleared. If the weapon has blood or tissue, mark the package with a biohazard label. Again, this label is important because it will alert the lab to safety issues and will also indicate that biological testing needs to be done before ballistic testing. Also remember that the ammunition from firearms should be packaged separately.

Arson evidence also requires special packaging. For this type of evidence, you need packaging that will prevent vapors from escaping. Since you’ll be looking for traces of accelerant, you may be collecting pieces of burnt wood, clothing, furniture, etc.; again, specialized packaging is needed. You can use clean, new metal paint cans in quart and gallon sizes, which can be sealed up easily, or heat sealed nylon arson bags. Don’t use traditional vapor barrier bags, which are made of oil based products that will interact with any accelerants that might be present in your evidence.

In some cases, you’ll also need to package liquids and powders. If you find an open soda can, pour the liquid into a vial and place the can in a paper sack. Remember to seal and label both containers. Paper folds and coin envelopes are good for collecting powders, tablets, etc. Place these items into larger envelopes to avoid losing them.

Knowledge of proper evidence packaging goes a long way. Many law enforcement property rooms and state crime laboratories have their own specific guidelines for how evidence should be packaged and submitted. Familiarize yourself with their protocol. Go to your local lab. Ask how they want evidence packaged. Contact your state association for property and evidence handling for information. Check with The International Association for Property and Evidence, which provides education and training on all aspects of evidence handling, storage, and maintenance. The evidence you collect could make or break the case. Take the time to preserve its integrity and give your case the best shot at success.

Dick Warrington is in research and development and a crime scene consultant and training instructor for the Lynn Peavey Company.