coroner (n.)

title of a county or municipal officer with certain duties, mid-14c. (mid-13c. as a surname), corouner, from Anglo-French curuner, from Anglo-Latin custos placitorum coronae (late 12c.), originally the title of the officer with the duty of protecting the private property of the royal family, from Latin corona, literally "crown" (see crown (n.)).

In the Middle English period an elected county or borough officer charged with the supervision of pleas of the Crown and the administration of criminal justice.  The duties of the office gradually narrowed and by 17c. the chief function was to determine the cause of death in cases not obviously natural.