A 42-year-old woman is brought to the mortuary 24 hours after being found unresponsive at home. The body shows fixed purple-red discoloration on the back and posterior thighs, with no blanching on pressure. The face is pale. Core body temperature is 22°C (ambient 25°C). The forensic pathologist notes that the livor pattern does NOT match the body's current position (body is supine, but livor is on the back as if the body had been prone). What is the most appropriate next investigative step?