Who needs autopsy?

Varies: In the usa, any death we suspect is a homicide or an indicator of a public health threat (new epidemic, chance of bioweapons), autopsy is the rule. The law may order autopsy on any suspicious / unexpected death, possible accident, suicide, or medical mishap. Or a family may request one -- nowadays there may be a charge.

Depends by state: Deaths in ohio are required to be reported to the coroner/medical examiner when "any person dies as a result of criminal or other violent means, or by casualty, or by suicide, or suddenly when in apparent health, or in any suspicious or unusual manner..." they will then investigate the circumstances and evaluate if an autopsy is necessary. However, family can always request one by the hospital.