Crime Scene Investigation
Crime Scene Investigation
Scene processing is the term applied to the series of steps taken to investigate a crime scene. Although the methods and techniques may differ between the experts involved, their goals are the same: to reconstruct the exact circumstances of the crime through the identification of the sequence of events and to gather physical evidence that can lead to the identification of the perpetrators.
Crime investigation usually begins at the place where the crime was committed. The area must be isolated and secured to prevent the destruction of crucial physical evidence that can lead police to link the perpetrators to the victim. The size of the area to be isolated and secured varies with each case, and a series of protocols designed to secure and protect evidence are followed.
The first police officer on the scene is responsible for preventing other non-essential police personnel and civilians from entering the scene and often establishes a perimeter around the crime scene with ropes or tapes. If witnesses are present, they are identified and remain outside the perimeters of the crime scene while waiting for questioning by the investigation team. If a death has occurred, a coroner, a crime scene technician, and investigators are requested to the scene to assist the police.
The crime scene technician is an expert in finding and identifying physical evidence such as hairs, fibers, empty bullet capsules, bloodstained objects, and body fluids which may be found in carpets, on furniture, on walls, etc. The scene and each piece of evidence is carefully photographed and then properly collected and conditioned to avoid contamination, to be later analyzed at the crime laboratory. This expert also writes a thorough report of the scene and describes the evidence found.
The investigator interviews witnesses, gathers information from the police on the scene, the crime scene technician, the coroner, pathologist, and other specialists that are present (such as a forensic anthropologist). The investigator is also responsible for the management of information given to the press, deciding what should or should not be initially disclosed to the public in order to not endanger the success of the investigation. The investigator will discuss with the prosecutor’s office the available evidence and other information to determine the legal direction of the investigation, since both are responsible for the entire investigative process and for building a case when prosecuting persons charged with the crime.
The coroner or medical examiner on the scene instructs the pathologist as to what physical evidence should be collected from the corpse and determines how the victim was killed and what caused the death. The coroner or medical examiner is also the liaison person between the crime scene technician, the pathologist, and the investigators, providing useful information that can either identify the murderer or yield important leads. The pathologist collects physical evidence from the body, such as chemical or metallic residues, body fluids, hairs, or skin residues under the nails. DNA content from such organic samples may be compared against CODIS (the Combined DNA Index System) to verify whether it belongs to a
known criminal, or it can be compared to other samples collected from specific suspects.
For investigative purposes, the area of a crime scene is always larger than the actual site or room where the crime occurred. Therefore, the first officer on the scene must be trained to identify and isolate the primary and secondary areas of the scene. If a body was found indoors, for example, the crime scene primary area is the room where it was found. The secondary crime scene perimeter is the remainder of the house or building, along with all the doors, windows, and corridors that give access to the primary area, including front and back yards. The secondary areas may contain important evidence of a fight, footwear prints, fingerprints, broken windows or doors, tire prints, or bloodstains.
In cases when a highly probable suspect is known, the suspect’s house or car may also be treated as a secondary crime scene area, even when it is not located in the proximity of where the crime was committed. All physical evidence identified in both areas may help in the reconstruction of the chain of events of the criminal act.
The services of a forensic anthropologist are requested when highly decomposed or charred human remains are found, when difficulty in gathering physical evidence is experienced, or when the identification of the victim or the cause of death is not apparent. A series of physical changes and interactions with soil bacteria, insects, and animals takes place when humans are buried, especially in mass graves. In these cases, the anthropological analysis of hair, bones and soft tissues (if available) may reveal race, gender, stature, approximate age at the time of death and, often, the cause of death. The conduction of
evidence gathering in these cases is a different procedure, usually not familiar to most crime scene technicians, and involves archeological techniques, soil analysis, identification of buried debris, recognition of buried marks of hands or footwear, and animal evidence.
Forensic anthropologists are often consulted for “cold case” investigations when human remains are unexpectedly found. These scenes should also begin with securing of the scene by the police, in case a determination is later made that a crime was committed. At least 10 yards around the spot where the remains are (or are believed to be buried) should be isolated. The anthropological gathering of evidence will take at least a full day, and when the remains are buried, two days. Only after this phase is completed can the remains be removed from the site. Forensic anthropology techniques may supply not only relevant physical evidence but also contextual information about the circumstances of the death, through the three-dimensional mapping and analysis of the scene, the location and interrelationship of physical evidence scattered around the remains, depth of the grave or pit, and geological characteristics of the soil.