Although the crime scene can include other locations where evidence may be gathered pertinent to the investigation, the preliminary homicide investigation must begin at the location where the body is first discovered (primary crime scene). The cardinal rule in homicide cases is to protect and preserve the crime scene. The first officer on the scene must secure the immediate area and establish boundaries of the scene. Since it is impossible to know the exact boundaries of the scene, the best course of action is to clear as large an area as possible and to make a quick and objective evaluation of the scene based on the location of the body, the presence of any physical evidence, eyewitness statements, and the presence of natural boundaries. Both the primary crime scene and any other locations related to that scene must be protected from entry by unnecessary or unauthorized persons so that physical evidence will not be altered, moved, destroyed, lost, or contaminated. Scene protection may be as simple as shutting a door to the room where the body is discovered but may also involve the use of ropes, barricades, autos, additional officers, and even volunteers from the crowd. Other locations related to the primary crime scene may include the point of forced entry, the route of escape, the suspect himself (his clothing, hands, etc.), the location where the weapon or any other physical evidence may be located, a vehicle used in the crime, the suspect's residence, and the location of the assault. Common crime scene contaminators include the weather, relatives and friends of the victim, suspects or associates, curious onlookers, and other members of police agencies. Examples of physical evidence found at crime scenes are listed.