What is the postmortem interval (PMI) defined as?

• A. The time elapsed since death, calculated using insect activity.
• B. The time since death based on heart rate and body temperature.
• C. The estimated time since death using only ambient temperature.
• D. The time since death measured by dental records and clothing.

Answer: (A)

PMI is the time elapsed since death. In practice, using insect activity provides a reliable clock because the arrival and development of insects on a body follow a predictable sequence that is driven by temperature and environmental conditions. By identifying the species and assessing the developmental stage of immature insects (eggs, larvae, pupae), and applying published growth rates, investigators estimate how long the body has been exposed. This approach often uses accumulated degree hours or days to translate development progress into an estimated time since death.

Other ideas like using heart rate changes or body cooling (ambient temperature) aren’t as reliable because cooling depends on many variables (body size, clothing, airflow, humidity, environment), and postmortem heart activity is not a direct measure of time since death. Relying on ambient temperature alone ignores how individual and scene factors affect the rate of cooling. Using dental records or clothing helps identify who the person was or describe the scene, not the timing of death.