A County Coroner may be called to examine a dead body if they died in an unanticipated manner. The County Coroner will then identify the person, if need be, and determine how they died and what their manner of death was: homicide, suicide, natural, etc.
A good County Coroner will serve as a regular coroner for a decent amount of time, and will have an advanced understanding of the human body. They will also have an expertise in the forensic skills required of their profession.
The County Coroner preserves order in society by identifying potential foul play, and by giving closure to families that need it. A bad coroner could rule something a suicide when it is a homicide, which could lead to unnecessary trouble.