The separate murders of two women in Toronto ignite an investigation that spans four decades, taking detectives from the big city to a remote, northern town. The case is finally cracked when diligent old-fashioned detective work is combined with modern breakthroughs in genetic genealogy.

NEW INTERVIEWS WITH: Det. Stephen Smith, Det. Andrew Doyle, Det. James Atkinson, Sean McCowan, Ben Tice, Vanessa Vansittart and Kristin Basso.

A Southern California woman's fall down the stairs initially appears to be a fatal accident, but when deputies arrest her husband, his story unravels. For the first time, the victim's family speaks out to Dateline correspondent Keith Morrison.

INTERVIEWS WITH: Theresa Neubauer, Frank and Samantha Gaulden, Peter Arsuaga, Kim Gadberry, Kristi Christensen, Jon and Rochelle Brannon.