A Crime Scene Investigator (CSI) is a professional who is trained to analyze crime scenes, collect evidence, process that evidence, and return reports which can be used by law enforcement officials and members of governments. The requirements for this job vary widely, depending on the organization doing the hiring and national standards. In some regions, Crime Scene Investigators are also sworn law enforcement officers, with the ability to arrest suspects and pursue various leads in the case, while others are civilians who have more limited abilities.

Most Crime Scene Investigators work either for a law enforcement agency or a company which needs trained investigators, such as an insurance agency which might send an investigator to the site of a car accident to determine whether or not the insurance agency will pay for the accident. Typically, an organization has a tiered system for CSIs, just like the system used for law enforcement. A Crime Scene Investigator must have different qualifications to reach various tiers; the more qualified, the more money a CSI can potentially make.

In the lab, a Crime Scene Investigator can process evidence to lift fingerprints and gather information about the site of the crime. For example, a CSI might look for hair, skin, or fiber samples so that a case can be built up against a suspect. A Crime Scene Investigator might also use various techniques to lift fingerprints from evidence so that these fingerprints can be used in the course of the investigation. Some CSIs actually specialize specifically in fingerprints, and they pride themselves on being able to lift fingerprints from almost anything.

In the field, a Crime Scene Investigator secures a crime scene to ensure that no evidence is compromised. He or she collects any and all evidence which might have a bearing on the case, and the CSI is also responsible for maintaining a chain of custody for the evidence to ensure that it is not compromised between the field and the lab. Some field investigators specialize in forensic photography, documenting crime scenes with the assistance of a camera; many CSIs use very high quality digital cameras so that they can instantly check on photo quality and take additional shots if needed.

Working conditions for a Crime Scene Investigator can be tough. CSIs are often on-call, meaning that they can be called out to a crime scene at any time. The job can also be emotionally grinding or very frustrating. Many CSIs spend a lot of time on their feet and a fair amount of time driving, and a Crime Scene Investigator must also be prepared to testify in court, and sometimes to defend his or her findings against various challenges. The position can also, of course, be very rewarding when a criminal is brought to justice.