Setting: Small town Indiana (US), Present day.
Search terms: Suspected foul play, Death ruled accidental, Who determines cause of death, How long does autopsy take, Nest material, Can a homicide later be ruled accidental.
MC loses her parents to carbon monoxide due to a blocked furnace flue. Detectives suspect that MC may have tampered with the furnace flue, but the deaths are ultimately (and correctly) ruled accidental.
A repair worker sent to MC's parents house finds a bird or rodent nest in the furnace flue. Among the innocent looking materials, torn remnants of clothing (t-shirt?, socks?, underwear?) belonging to MC are found in the nest. Because the incident occurred on the first night of the heating season, the nest could have been in the flue for weeks or months before the incident. Possible motive comes from MC having arguments with her mother prior to the incident. MC is a former employee of a company that installs heating and air conditioning equipment and the detectives (mistakenly) believe that she may have gotten the idea/knowledge at her old job.
How long would it take for MC to be exonerated and the deaths to be ruled accidental? Out of the people involved (detectives, forensic examiners, coroner, etc.), who would be primarily responsible for clearing MC? The cause of death is confirmed to be carbon monoxide poisoning for both parents, so ruling out foul play would depend on how the flue became blocked, not how MC's parents died.