The purpose of crime scene investigation is to help establish what happened (crime scene reconstruction) and to identify the responsible person. This is done by carefully documenting the conditions at a crime scene and recognizing all relevant physical evidence. The ability to recognize and properly collect physical evidence is oftentimes critical to both solving and prosecuting violent crimes. It is no exaggeration to say that in the majority of cases, the law enforcement officer who protects and searches a crime scene plays a critical role in determining whether physical evidence will be used in solving or prosecuting violent crimes. Documenting crime scene conditions can include immediately recording transient details such as lighting (on/off), drapes (open/closed), weather, or furniture moved by medical teams. Certain evidence such as shoeprints or gunshot residue is fragile and if not collected immediately can easily be destroyed or lost. The scope of the investigation also extends to considerations of arguments which might be generated in this case (suicide/self-defense) and documenting conditions which would support or refute these arguments. In addition, it is important to be able to recognize what should be present at a scene but is not (victim's vehicle/wallet) and objects which appear to be out of place (ski mask) and might have been left by the assailant. It is also important to determine the full extent of a crime scene. A crime scene is not merely the immediate area where a body is located or where an assailant concentrated his activities but can also encompass a vehicle and access/escape routes. Although there are common items which are frequently collected as evidence (fingerprints, shoeprints, or bloodstains), literally any object can be physical evidence. Anything which can be used to connect a victim to a suspect or a suspect to a victim or crime scene is relevant physical evidence. Using the "shopping list" approach (collecting all bloodstains, hairs, or shoeprints) will probably not result in recognizing the best evidence. For example, collecting bloodstains under a victim's body or shoeprints from emergency personnel will rarely answer important questions. Conversely, a single matchstick (not usually mentioned as physical evidence) recovered on the floor near a victim's body can be excellent physical evidence since it can be directly tied to a matchbook found in a suspect's pocket.
Interested in the infamous unsolved murder of Elizabeth Short, aka the “Black Dahlia,” the 22-year-old Hollywood starlet who was brutally murdered in Los Angeles 60 years ago this January? If you don’t know the story, Short—dubbed “Black Dahlia” by the press for her rumored penchant for sheer black clothes and for a movie at that time—was found sliced clean in half at the waist by a mother walking her child in an L.A. neighborhood just before 11 a.m. on January 15, 1947. The body was just a few feet from the sidewalk and posed in the grass in such a way that the woman reportedly thought it was a mannequin at first. Despite the extensive mutilation and cuts on the body, there wasn’t a drop of blood at the scene, indicating Short had been killed elsewhere. An extensive manhunt followed, but the killer has never been identified.