The location of a suspected criminal incident is usually referred to as the crime scene. In some cases, it may be obvious that a violent or otherwise illegal activity has taken place. In others the crime scene investigator will be initially tasked with establishing whether a crime has been committed and conducting a forensic investigation. The investigation is the process of ascertaining facts, conducting a detailed and careful examination to conclude what might have happened and who did it. The scenes of vehicle accidents, accidental or sudden deaths, suicides, suspected homicides, theft, fraud, sexual assaults, fires and drug investigations are all examples of potential crime scenes.
Crime scene locations are labeled as primary and secondary. The primary location is the area in which the incident occurred or where the majority of physical evidence will be found. Secondary locations contain physical evidence relating to the incident, which may include items transported away from the primary location, like vehicles, weapons and bodies. Use of the word investigation within the context of crime scene analysis encompasses the identification, recording and collection of all potential evidentiary material and the interpretation of the circumstances surrounding the crime by reconstruction techniques, which attempt to reveal the modus operandi. The practice of crime scene investigation requires specialist skills, knowledge and aptitude. Accordingly, a disciplined approach and systematic application of various observation, recording and collection techniques are needed.
The management and co-ordination of crime scenes requires three things: The resources to carry them out, the technical equipment to record and recover potential evidence, and establishing an interpretation of what has occurred in the recent past. Investigations involve a variety of specialist methods depending on the nature of the crime. Examples of these include DNA profiling and a number of areas of forensics, including psychology, pathology, anthropology, optometry and toxicology. Forensic science is a powerful aid to criminal investigation within the courts. Good management of crime scene investigations involves and depends on various factors, from scene security, occupational health and safety, documents and records management, preventative and corrective action and laboratory information management, to quality assurance, court reports and court processing. Approaching the crime scene, containing the evidence and documenting relevant information are key steps in a thorough and conscientious investigation. The investigator considers and collates as much information about the crime as possible, covering the locations the crime is connected to, people who may be connected to the crime directly and indirectly, and the timings of activities relevant to the case.
Crime scenes are broken down into zones to be examined more thoroughly. Areas of particular interest include the point of entry, surrounding area and, in the case of murder, location of a body. Police barrier tape may cordon these areas off to the public if necessary. Preserving evidence at its most useful is important to scientific investigation; therefore factors such as the weather and location may impact on finding clues. Crime scene photography gives an accurate and permanent record of evidence as it is found. Warlen (1995) suggests that photographs can help witnesses recall events and assist the clarity of witness statements when used in court. It can assist with evidence being reassembled, re-inspected and reviewed throughout the investigation.
Criminal profiling analyses details from the scene that provide possible insights into the type of person responsible for the crime – possible motivations, glimpses of their lifestyle, their fantasies and victim selection process, and behavior of the suspect before and after the incident. Criminal profilers use police reports, photographs, witness statements, laboratory reports, and autopsy photographs to search for behavioral details. This process allows the profiler to understand and create an idea of the crime and offender. Interpreting behaviors will help the investigator narrow down the suspect list and structure the investigation process.
Fingerprint analysis remains widely used in the identification of criminals. All fingerprints are unique, and studies show that ridge patterns on fingertips remain the same throughout a person's lifespan, save for natural growth, accidents, mutilation or skin disease. Powders, chemical reagents or high intensity light sources are methods to capture the impression of an individual's fingerprint, which is easily collected as evidence. DNA testing is also used to assist identification of individuals using well established methods of molecular biology. Forensic scientists can then compare the DNA from a crime scene to a defendant. Matching DNA to that found at a crime scene is powerful evidence.