A 19-YEAR-OLD COLD CASE TURNS HOT WHEN INVESTIGATORS "KNOCK ON THE DOOR" OF THE VICTIM'S WIDOW -- "48 HOURS MYSTERY," APRIL 15

There is no statute of limitations on murder, just ask Mark Mangelsdorf and Melinda Harmon Raisch. Mangelsdorf went to Harvard and is a prominent executive in New York. Raisch is a soccer mom married to a successful Columbus, Ohio dentist. But, now, both are charged with a horrific murder that took place more than 20 years ago -- a case gone very cold until the day police came knocking on their doors.

Hannah Storm, co-anchor of THE EARLY SHOW, reports for 48 HOURS MYSTERY: "A Knock on the Door," to be broadcast Saturday, April 15 (10:00-11:00 PM, ET/PT) on the CBS Television Network.

In 1982, in the tiny town of Olathe, Kan., outside Kansas City, a young banker named David Harmon was bludgeoned to death in his bed. His wife Melinda told authorities that two men intent on robbing the bank where David worked had broken into their house and committed the crime. At the time, authorities had serious questions about Melinda's story. They believed, but could not prove, that Melinda was caught up in a secret affair with family friend Mark Mangelsdorf, and that the two were involved in David's murder. It would take two decades and new forensic technology for police to zero in on the couple again.

Mangelsdorf, facing murder charges in Olathe, granted Storm his only television interview. An independent business consultant in New York City, Mangelsdorf is now married with five children and lives in Pelham, N.Y. He denied that he or Melinda, now the mother of two, had anything to do with David's death. But, the dramatic conclusion of "A Knock on the Door" finally reveals the dark truth.

48 HOURS MYSTERY: "A Knock on the Door" is produced by Lisa Freed and Deborah Grau. The executive editor is Al Briganti and the executive producer is Susan Zirinsky.