Crime scene investigators, or alternatively crime scene technicians, are law enforcement personnel who document and process evidence from crime scenes. They are responsible for identifying and securing the scene, documenting the state of the scene and collecting evidence.
Securing the Scene
Upon their arrival the investigators' top priority is to ascertain the extent of the crime scene and secure the perimeter to prevent contamination or removal of evidence. Law enforcement personnel can block off the area with tape or barricades and only allow essential staff to enter the premises.
Scene Walk-Through and Documentation
Once the area has been secured, investigators do an initial walk-through to more closely examine and document the state of the crime scene as it was found. They especially take careful note of any important conditions that could change over time such as the room's temperature, or fluids in the area that have not yet dried. Crime scene investigators and/or a forensic photographer document the overall scene and individual portions of it via photographs and video.
After the entire scene has been documented, investigators begin the search for specific pieces of evidence. This can include trace evidence (such as fibers or hair), footprint or tire impressions, fingerprints, blood or other bodily fluids and weapons. The evidence is collected using tweezers, gloves or tongs to prevent contamination. In some cases entire portions of a wall, floor or large furniture may be removed for further analysis by forensic scientists.
Evidence Storage and Testing
Investigators document, seal and label all evidence for transportation to a crime lab for analysis. Depending on the type of evidence and the size of the police agency or department, some evidence may be tested on the premises while others are sent to specialists for further examination. Crime labs can conduct a variety of types of testing: chemical analysis, microscopic examination, fingerprint analysis, DNA testing and matching, toxicology tests and more.