duty officer 
noun
An officer, especially in the police or armed forces, who is on duty at a particular time.The duty officer ordered police not to confront the offenders but to call for back-up from nearby stations....
- If cells reach capacity the duty officer informs other officers to take suspects to neighbouring boroughs.
- After the word went out of the motorcyclist's death, the gun-totting prince went to the local police station and threatened the duty officer with dire consequences if the incident was made public, according to the reports.