In those counties in which a coroner does not reside or is not available, the duties of a coroner must be performed by the sheriff, state highway patrol, or any special agent of the bureau of criminal investigation. The sheriff, state highway patrol, or special agent shall call upon a coroner or deputy coroner from another county to investigate the medical cause of death of all coroner cases within the county. In those situations in which, because of distance or adverse conditions, a coroner is not available, the sheriff, state highway patrol, or special agent shall request the state forensic examiner or the forensic examiner's designee to investigate and certify as to the medical cause of death.