After evidence has been found and gathered, it must be protected. Each piece of evidence gathered is packaged separately to avoid damage and cross-contamination. Most dry trace evidence is placed in druggist's folds, which are small, folded papers. Envelopes, canisters, plastic pill bottles, and paper or plastic bags may also be used. Documents are sealed in plastic covers before they're transported to the lab.
Liquid evidence, on the other hand, usually is put into unbreakable, airtight, sealed containers. The same is true for solid forms of evidence that may contain volatile evidence, such as charred remnants of a fire that are believed to contain residues of hydrocarbon accelerants (substances such as gasoline or kerosene that make a fire burn faster and hotter and are commonly used by arsonists). Left unsealed, these residues can evaporate before they are tested. Clean paint cans and tightly sealed jars work well for evidence in solid form.
Moist or wet biological evidence must be placed in nonairtight containers so that it can air dry; otherwise, the moisture can cause mold, mildew, and bacterial growth, which, in turn, lead to decay and ultimately destroy the sample. Bloody clothing often is hung up and allowed to thoroughly air dry. After the biological evidence is dry, it is repackaged into sealed containers.
Sometimes removing evidence from the scene without damaging it is difficult or even impossible. A tool mark on the sill of a window that's been pried open can be processed at the scene, or the entire window or frame may be removed and taken to the lab. Similarly, bullet holes in a concrete wall may be processed on-site, or a portion of the wall may be carefully removed for later laboratory evaluation.