The disturbing cases of Raymond Rowe and William Talbott show that one-and-done killers are among us by the thousands, and might never be found without genetic genealogy. But will authorities be allowed to keep using it?    To follow the Unraveled investigations even further, stream the specials exclusively on discovery+. Go to discoveryplus.com/unraveled to start your 7-day free trial today. Terms apply. See acast.com/privacy for privacy and opt-out information.