Every day, nearly 7,000 people in America die. And when the deaths are unexpected, sudden or suspicious, it's presumed that a thorough investigation will take place.

Though you might expect a thorgough and high-level investigation from TV shows like CSI, the reality is quite different. In over 1,300 counties across the United States, elected coroners are in charge of death investigations –  many with no medical or scientific background. To run for coroner in most counties, all you need is a high school diploma.

Lowell Bergman  has investigated the consequences of this reality for a new Frontline documentary called "Post Mortem," which airs Tuesday night on PBS.