Watchful Eye

On May 20, 2001, Carrie Nelson, then 20, was beaten to death while working alone in a state park office. There's a wealth of evidence at the scene, but it didn't implicate the prime suspect, it cleared him. The case went unsolved for six years until May 2007 when, in a routine check of DNA samples of prison inmates in South Dakota, police found a match with DNA samples gathered from the crime scene.