Evaluation of the crime scene Evaluating a scene before anyone enters can be key to keeping contamination to a minimum.
Protecting the crime scene The most important aspect of
evidence collection and preservation is protecting the crime scene. This is to keep the pertinent evidence uncontaminated until it can be recorded and collected. Eating, drinking, or smoking should never be allowed at a crime scene.
Documentation of the crime scene The taping should begin with a general overview of the scene and the surrounding area. The taping should continue throughout the crime scene using wide-angle, close up, and even
macro (extreme close up) shots to demonstrate the layout of the evidence and its relevance to the crime scene. Liquid items can be transported in non-breakable, leakproof containers.
Arson evidence is usually collected in air-tight, clean metal cans. Only large quantities of dry powder should be collected and stored in plastic bags. Moist or wet evidence (blood, plants, etc.) from a crime scene can be collected in plastic containers at the scene and transported back to an evidence receiving area if the storage time in plastic is two hours or less, and this is done to prevent contamination of other evidence. Once in a secure location, wet evidence, whether packaged in plastic or paper, must be removed and allowed to air dry completely. That evidence can then be repackaged in a new, dry paper container. Under no circumstances should evidence containing moisture be packaged in plastic or paper containers for more than two hours. Moisture allows the growth of microorganisms which can destroy or alter evidence. Any items which may cross-contaminate each other must be packaged separately. The containers should be closed and secured to prevent the mixture of evidence during transportation. Each container should have the collecting person's initials, the date and time it was collected; a complete description of the evidence and where it was found; and the investigating agency's name and file number.
Tools Not only is the actual crime scene as a whole important to protect in order to avoid contamination the tools used pose just as big of a threat. Simple measures can be taken by an investigator to ensure the integrity of
DNA evidence. Tools can easily transfer DNA from one crime scene to another. Fingerprint brushes, for example, can retain the DNA they pick up and create contaminated evidence. In order to ensure there will not be a transfer of DNA on brushes, they should not be reused. Each scene should get a new one. This tip is especially important in situations like
homicide cases, where DNA is a crucial factor. Paying the extra six to nine dollars for an extra brush may be the difference in contaminated evidence and alleviating questions. Gloves are another tool that needs to be carefully handled at a crime scene. There is no guarantee that gloves will permit contamination. The key is to change gloves often. If one fails to do so, they can be contaminated by obvious reasons like touching blood and other fluids, but also simple movements such as covering your mouth when you sneeze and scratching your face. Like brushes, gloves are extremely cheap and should be disposed of and changed whenever they may have been compromised. == Cases ==