In order to assist a prosecutor in criminal investigation, the law manifestly specifies the following offices as the facilitating bodies so as to ensure effective exercise of the prosecutorial function.

Judicial police officer:
Those who has the duty to assist a prosecutor in investigation a crime are:
county magistrate or mayor.
the head of a police department, commissioner of police or commissioner of public safety.
military police officer
Those who shall follow the instructions of a prosecutor in investigating a crime are:
Commissioned police officers.
Military police officers or non-commissioned officers.
Persons who are authorized to exercise the duties of a judicial police officer in specific matters.
Judicial policemen:
Those who shall follow the order of a prosecutor in investigating a crime are:
policemen
military policemen
persons who are authorized to exercise the duties of judicial policemen in specific matters.