The Role of the Crime Scene Investigation Unit

The Crime Scene Investigation, or CSI unit, is the group of individuals within a law enforcement agency that is responsible for processing crime scenes and collecting evidence. It is the responsibility of CSI technicians to document the crime scene and to maintain the integrity of the chain of evidence.


CSI technicians carefully document the crime scene with sketches, written notes, photographs and videos. They use measurements to accurately record the location of objects and take special care to note any conditions that could be transitory, such as the presence of a particular smell. As technicians document the scene, they also pay careful attention to the locations of evidence and prioritise its collection according to the potential for degradation or contamination. Technicians take photographs of the overall state of the scene as well as close-ups of evidence.

Examining the Body

Where there is a murder, or a suspected murder, the CSI team conducts an examination of the body and the area around it before it is removed by the coroner or pathologist's office. CSI technicians are not involved in the autopsy, which is handled by a pathologist. Rather, they analyse the positioning and condition of the body as it was found at the scene and collect any evidence. They document the state of dress (or undress), any decomposition and its extent, insect activity, apparent injuries and blood stain patterns, positioning of the body and other important details. CSI technicians also collect evidence, such as hair or fibres.

Collection of Evidence

After they have documented the crime scene, CSI technicians begin collecting evidence. In order to avoid missing any evidence, they use specific search patterns to cover the entire crime scene. Collecting evidence, technicians must keep in mind the goals of both preserving and collecting it in a way that will allow it to be used in court. Items that might be collected as evidence include fingerprints, tire or shoe impressions, bodily fluids, hair, fibres or dirt and any other items that might assist technicians in reconstructing the crime or identifying a suspect. Technicians must be careful not to contaminate evidence, which is picked up with gloves, tweezers, tongs or other equipment. They seal and label all evidence for transport to a crime lab for analysis.

Analysis of Evidence

Evidence is taken to a law enforcement agency's crime lab for analysis after it has been collected. In some cases, certain items may be sent to forensic specialists for further testing. In smaller agencies, the crime scene technicians and lab technicians often are the same individuals; however, in larger law enforcement organisations, these duties are typically divided between two different sets of investigators. Lab technicians use a variety of scientific techniques, such as DNA typing, microscopic examination, fingerprint comparisons and toxicology testing, to analyse evidence.

Other Duties

Crime scene investigators, in addition to completing investigative and lab duties, must be able to communicate their findings to others. They are required to meet with other investigators and attorneys to discuss their findings and to create reports and presentations. Additionally, crime scene investigators are frequently called upon to appear in court as expert witnesses. Although there are no federal or state licensing requirements for CSI technicians, individual agencies generally require employees to participate in continuing education activities.