After 30 years, Detective Jim Scharf arrested a teenage couple's murderer—and exposed a looming battle between the pursuit of justice and the right to privacy. When Tanya Van Cuylenborg and Jay Cook were murdered during a trip to Seattle in the 1980s, detectives had few leads. The murder weapon was missing. No one witnessed any suspicious activity. And there was only a single handprint on the outside of the young couple's van. The detectives assumed Tanya and Jay were victims of a serial killer, but without any leads, the case seemed forever doomed. In deep-freeze, long-term storage, biological evidence from the crime scenes sat waiting. Meanwhile, California resident CeCe Moore began her lifetime fascination with genetic genealogy. As DNA testing companies rapidly grew in popularity, she discovered another use for the technology: solving crimes. When Detective Jim Scharf decided to send the cold case's decades-old DNA to Parabon NanoLabs, he hoped he would bring closure to the Van Cuylenborg and Cook families. He didn't know that he and Moore would make history. Anyone can submit a saliva sample to learn about their ancestry. But what happens after the results of these tests are uploaded to the internet? As lawyers, policymakers, and police officers fight over questions of consent and privacy, the implications of Scharf's case become ever clearer. Approximately 250,000 murders in the United States remain unsolved today. We have the tools to catch many of these killers—but what is the cost?