15-year-old cheerleader Kirsten Costas is stabbed to death in California. A teenage girl is seen fleeing the scene. As months pass without an arrest, the police are stumped. But some in the community think they know the murderer.For even more Deadliest Decade, head to discovery+. Go to discoveryplus.com/deadliestdecade to start your 7-day free trial. Terms apply. Hosted on Acast. See acast.com/privacy for more information.