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Crime scene investigation is the first step in the use of forensic evidence to solve a crime. During this phase of a criminal investigation, items at the scene are found, collected and analyzed preliminarily in order to determine how a crime was committed. To accomplish this, crime scene investigators must follow procedures that include managing the crime scene; securing, surveying and documenting it; and collecting and preserving evidence.
Securing the Scene
In order to ensure that evidence is protected, the first person at the scene of a crime should secure it with barriers and/or crime scene tape soon after arriving to the crime scene. In addition, someone should be chosen to act as a security guard so that people who do not belong at the location are kept out.
Managing a Crime Scene
At every crime scene, there are several people walking around performing different tasks. It is imperative that the investigator in charge manage the logistics of the scene, the personnel who are there, the information that is disseminated to all of the players involved and the technology being used. This level of communication is necessary because what happens during the crime scene investigation phase can make or break a case.
Surveying the Scene
This phase of crime scene investigation, which can include an investigator and a police officer, involves looking at the entire scene and forming early theories about what may have occurred during the crime. It is important for the investigators not to make any snap decisions when they perform this task as these hypotheses are subject to change based on pursuant forensic examinations.
Documenting the Scene
Crime scenes are documented by four methods: written notes, photos, videos and sketches. Each step of documentation is important because it serves as the record of the scene long after the evidence has been taken to forensic examiners and the location has been cleaned up. All of these forms of documentation are equally important to the case, so one should not be overlooked in favor of another.
Searching the Scene
The search is performed by investigators based on what was observed during the earlier survey of the crime scene. During this stage of crime scene investigation, the order in which evidence will be collected is established.
The lead investigator at a crime scene will elect one person to collect and preserve all of the evidence, which makes it more likely that every item is accounted for and that the evidence does not get lost or become contaminated. Each piece of evidence is handled carefully, packaged separately and marked by the crime scene investigator.
Reconstructing and Releasing the Scene
During the reconstruction phase of crime scene investigation, more theories of a crime are developed---or disregarded---based on the evidence that was found and collected. When forensic scientists test the evidence, it is determined how accurate these theories are.
After investigators finish their work on a crime scene, the person in charge will release it. When this is done, the date and time of the release is documented by the lead investigator. In some cases, no one will be able to subsequently enter the crime scene unless a warrant is obtained.