Purpose

• The purpose of the crime scene investigation is to help establish how, when, where and what type of crime occurred. These elements can lead up to why a crime was conducted and who may have been involved. Because of the job's importance the investigator must be thorough, observant and unbiased. Collecting evidence is a fact driven occupation with no room for possible theories or speculation. A careful and thoughtful approach is the best path for the investigator to document conditions accurately and recognize valuable evidence.
  
  

Communication

• A thorough understanding and consideration for the type of crime scene being investigated is vital to the approach. Communication with other personnel working the case such as law-enforcement or a prosecuting attorney is necessary for a well-run search. This not only keeps everyone advised of findings but if a question or situation arises, the needed assistance will be readily available. With the more complicated investigations a headquarter area is often set up as a central discussion and decision-making post.
  
  

Approach

• It is imperative to maintain control of the crime scene. This keeps the site secure, eliminating contamination while maintaining evidence chain of custody. No one should be allowed into the scene, even unauthorized law-enforcement should be restricted. Everyone who has previously been at the crime scene should be documented while providing a statement of initial observations. This includes witnesses, neighbors or police. Never rely on memory, document everything.
  
  

Narrative

• Three main types of narratives are completed through writing, recording and photography. A recorded running narrative should be initiated at the investigation's onset, beginning with a broad perspective that narrows down to the specific. The purpose of this is to take into account conditions of the crime scene and all observations from more than one perspective that is useful when reviewing the case later. Noting objects or evidence to compare with the environment is also key in proving a crime was committed. Narratives should be conducted prior to collecting any evidence.
  
  

Photographs

• Photographs should be taken before the crime scene has been altered by a more detailed search. As with the narrative, photographs should be shot with a broad view, moving towards more detailed elements.These first photographs document the scene in its most original condition. Occasionally, elements initially unseen by investigators may appear later in photographs. Items and evidence should be photographed alone first then again with a measure or device that provides their accurate dimensions.
  
  

Physical Evidence

• More fragile evidence such as gunshot residue or footprints should be collected first. Afterward, the examination of more stable evidence is done. The purpose of looking at transient items first is their likelihood of being destroyed or lost. Another important key are areas of easy access. Entrances, exits and areas in open view should be examined first then progress methodically to obscured or purposely hidden areas. Always consider if the evidence appears to have been moved by design or if the scene itself may have been staged.
  
  

Basic Premises

• A thorough and complete crime scene search should observe four basic premises:
  A crime scene cannot be documented too much.
  The best searches are often the most difficult and time consuming.
  There is only one chance to perform the job properly.
  Search approaches should be conducted in two phases: the broader one, where all open and visible areas are documented in order to avoid evidence contamination; then a close and detailed search for concealed evidence.