Crime scene is the physical evidence that supports the events of a crime and may establish timelines and circumstantial indications of motive, opportunity and means. It can include such things as blood and other bodily fluids, fingerprints, clothing and trace evidence like tool marks, gun residue and odors. In addition, crime scenes may be analyzed for clues to the identity of suspects through a variety of investigative methods.
Upon arrival at a possible crime scene, police officers and forensic specialists attempt to disturb the area as little as possible and document it to record the initial conditions of the location. Then they conduct an initial survey/walkthrough to prioritize evidence collection. In doing so, the lead investigator will identify what is important to the investigation and capture initial photographs of the crime scene. This initial walkthrough includes the primary crime scene (the location where an assault or murder took place) and if applicable, other relevant areas, such as paths of perpetrator entry and exit.
In addition to photographing the crime scene, police officers also note important facts such as the weather at the time of the incident; any odors; the position and condition of doors, windows, furnishings and movable equipment (like cars); if the scene is inside or outside and the condition of nearby pathways or yards that may contain evidence. They also establish an initial pathway for themselves that avoids contamination of existing evidence. Whenever they leave the pathway to perform other duties, such as dusting for fingerprints or collecting evidence, they will be prepared to document their departure from the path and explain why it was necessary.