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Crime scene investigators must approach a crime scene as if it is the only chance they will have to assess the scene and process the evidence. Protocol requires approaching any and all crime scenes with caution. Taking note of every detail, including vehicles and persons leaving the scene and persons and vehicles in the vicinity that may be involved in the crime, is also part of the job. All must assume that the crime is still happening until they find out otherwise.
Scanning the scene for smells, sights and sounds that may indicate potential hazards to other arriving law enforcement, such as gasoline or natural gas leaks is also required. Investigators must contact the appropriate agency if chemicals or explosives are involved prior to entering the scene. Maintaining control of the scene while ensuring safety for themselves, the victims and any witnesses is paramount. Investigators should report regularly to dispatch and acquire backup if needed.
Next, investigators assess any victims for signs of life and medical need while avoiding contamination of the crime scene. They contact emergency services as needed, as well as guide emergency personnel to persons who require assistance. They point out any physical evidence to emergency personnel and caution them to avoid contact. If there is a chance a victim may die, investigators should attempt to acquire a dying declaration if the victim is conscious at all. Documentation of all accounts from victims and witnesses is also vital to the investigation.
Investigators should control and identify all persons at the crime scene. Both witnesses and suspects must be separated and secured. Any bystanders who are not witnesses must be removed from the scene. Boundaries of the crime scene, starting at the center and expanding to include the area where the crime happened, pathways, entries and exits, must be established. Individuals in the area should not touch anything in the vicinity, and smoking, eating, drinking, bathroom use and the repositioning of anything are prohibited. Any such movement should be documented.
Arriving investigators taking control of the scene should be given a brief. Documentation must include general observation and assessment of the crime scene upon the initial crime scene investigators' arrival, the conditions upon arrival including smells, open or closed doors and windows, temperature, location of all persons and objects and the weather conditions. Documentation of personal information of all victims, witnesses and suspects, including any statements made must also be provided.
Crime scene photography is the most utilized evidence, but other image documentation, such as sketches and video may be necessary. It is the responsibility of the lead investigator to ensure that the crime scene is documented in an effective manner.
A crime scene photographer must review the overall crime scene assessment with the lead investigator to determine the areas that need to be documented. The photographer must photograph the overall scene at multiple angles, as well as determine a mid range from which to photograph. All areas of the crime scene, victims, witness, evidence, crowd, vehicles and suspects at close range must be photographed.
The lead investigator determines the order in which evidence is collected from the crime scene. Members of the team collecting evidence must maintain the security of the crime scene at all times. They document the location, date and their name on evidence that they collect and package. They obtain and package both reference and control samples. Securing any electronically recorded evidence, such as answering machine tapes, computers or tapes from surveillance cameras is another responsibility. Documenting the condition of any weapons or firearms before rendering them safe for transport also falls under the lead investigation team. Evidence should not be handled with excessive force. Finally, everything must be packaged to prevent contamination or cross-contamination.
It is difficult to prioritize the different steps because failure to adequately perform one step (i.e., securing the scene) can adversely impact the other aspects of the crime scene investigation (i.e., collection of evidence). However, if forced to prioritize the securing of the scene and collection of evidence would be the most important given the ever increasing number of crimes solved and/or proven through use of forensic analysis of items collected.