Why would the police arrest someone for a possible homicide when it was a death due to natural causes?

Question

Why would the police arrest someone for a possible homicide when it was a death due to natural causes?

Answer

You need to provide more information. I can come up with scenarios such as a parent who allows a child with an infection to die rather than get them treatment - that is natural causes but the parent will be held responsible. A person with a responsibility of care for another sees that the person is in distress medically and does nothing for them could potentially be held responsible. You really need to provide more info.