A 58-year-old man is found dead in his apartment in Delhi. The body is discovered 18 hours after death. On examination, the forensic pathologist notes purple-red discoloration on the dependent surfaces of the back and buttocks, which blanches on pressure. The face and neck show cyanotic discoloration. Core body temperature is 28°C (ambient temperature 32°C). What is the most appropriate next step in establishing the time of death?