One day in mid-December 2003, Detective Mark Kelly walked into a small kitchen at a home in Fort Worth, Texas. The house belonged to a potential suspect in a homicide case, and while his partner was interviewing that suspect in the other room, Kelly was poking around. He wanted to hurry, because the kitchen he was in was disgusting. There was a layer of dirt on the floor, the dishwasher was open, with dirty plates and silverware still inside, dishes were stacked up in the sink, and used pots and rotting food covered the counters. Kelly could hear his partner talking in the other room as he grabbed the nearest drawer and pulled. Instantly, he regretted it. Because when he opened that drawer, about a dozen cockroaches crawled out of it. Kelly gasped and took an instinctive step back, watching the bugs skitter away. He was searching for a weapon, and it wasn’t here. But something about the filth felt like a clue. Kelly just didn’t know what it meant yet.