What is the first action to take when a detective relieves you during a preliminary investigation?

When a detective relieves you during a preliminary investigation, the first action to take is to brief the detective. This step is crucial as it ensures that the detective is fully informed about the details of the scene, the actions that have already been taken, and any pertinent information that has been gathered during the initial stages of the investigation.

Providing a comprehensive briefing allows for a smooth transition of responsibilities, helping the detective to understand the context and nuances of the case. It fosters effective communication and ensures that critical information is not lost or overlooked as the investigation progresses. This may include information about witnesses, evidence collected, and any initial findings or observations made during your presence at the scene.

The other options do not support an effective investigative process in the same manner. Communicating with the detective's supervisor or leaving the scene prematurely can disrupt the flow of information and hinder the investigation's integrity. Collecting evidence at this stage would also be counterproductive, as the detective may have specific protocols or methods they intend to follow in their investigation. Therefore, brief the detective is the appropriate first action.