If there's been foul play at the county jail, the hospital or in the mayor's bedroom, the medical examiner is the peoples' first and often best chance to uncover the truth.
Coroners and medical examiners aren't supposed to comment on or interpret what events transpired to cause a death. They only determine the time and cause of death. If a person dies of poisoning, it's not up to them to determine if it was accidental or murder -- that's for the police to sort out. By factually determining the cause of death without interpreting it, medical examiners are much less likely to skew the perception of investigators working a potential homicide.
The task is (supposed to be) objective, meaning that if medical malpractice, police brutality or an act of negligence is to blame, the medical examiner will provide a fact-based explanation for the cause of death, allowing the public to feel confident that the truth, no matter how ugly, will be exposed.
And medical examiners, as we'll see in the next section, can pick up the check.