What is the first step a CSI should take upon arriving at a crime scene?

The first step a Crime Scene Investigator (CSI) should take upon arriving at a crime scene is to secure the perimeter of the scene. This is crucial to ensure that the area is protected from contamination and tampering, which can compromise the integrity of the evidence. Securing the perimeter involves establishing a controlled boundary around the scene to keep unauthorized personnel out, allowing the investigators to work unobstructed. It also helps in maintaining the chain of custody for any collected evidence, as the scene can later be disturbed if not properly secured.

Once the scene is secured, the CSI can proceed with other important tasks such as documenting the scene conditions, collecting evidence, and interviewing witnesses in a systematic manner. Each of these tasks is significant and must be performed in the correct order to ensure the overall integrity of the investigation. Without first securing the scene, any subsequent activities could risk destroying critical evidence or altering the scene's condition.