Investigators walked into a mystery that would turn their world upside down… Watch tonight at 9/8c on a 2-hour Dateline Weekend Mystery on NBC. | Dateline NBC

Tonight on a new Dateline, the latest chapter in this hair-raising tale, featuring new evidence, explosive testimony and the prosecution's new star witness. Watch at 9/8c on NBC. | Dateline NBC

A medical mystery was about to turn into a full-on police investigation… Tonight on an all-new Dateline at 10/9c on NBC. | Dateline NBC

None of it made sense… What happened on that cold, brutal morning? Find out tonight at 9/8c on a classic Dateline on NBC. | Dateline NBC

Thirty-two years ago this month, a series of murders began near and along Virginia’s Colonial Parkway. When it was over, four couples were dead at the hand of what authorities believe could be a serial killer. The crimes were dubbed “The Colonial Parkway Murders.” | Dateline NBC