January afternoon in 2015, a medical examiner stood over a dead woman’s body in the county morgue. He’d already opened up the woman’s abdomen, and he was using his scalpel to cut the tissues around her stomach. The woman had been murdered, and the medical examiner had already determined her cause of death — but now, he was searching for something specific. He placed the stomach on a metal tray and sliced it open, revealing everything she’d eaten before her death. To his surprise, there was almost nothing there, which meant the woman hadn’t eaten for several hours. This struck the medical examiner as very odd, because detectives had told him that the woman bought Mexican food less than half an hour before her death, and they found the empty wrapper at the crime scene. But if the murder victim didn’t eat it, that left only one other possibility: her killer did. The medical examiner put his scalpel down and looked at the woman on his autopsy table