In the fourth and final episode, a former police officer who investigated the original case tells Mark he believes it is plausible that Russell could have burned Carole's body as a way to dispose of it as he claimed in his confession letter.Mark learns police recently visited Russell in prison to hold a meeting with him. Sam's son Neil contacts Mark to update him on developments. Neil says: "He [Russell] stands by what he said in the letter. The letter's completely truthful. Meyrick Park golf course was one of the locations he's given as where he scattered the ashes."Mark heads to the golf course to see whether he can find any evidence, 30 years on.Russell identified a broad area in his garden where he claims to have burnt his wife's body before scattering her ashes at different locations around the country, so Mark instigates a dig, and asks a specialist in cremated remains to investigate the claim. Sam has a brief recollection of the fire in June 1985. She says: "When I came home, my father was stood up on the bank with the fire … My father was really, really angry with me. And he ripped my dress and he sent me into the home."Also, more letters arrive from Russell which add a further twist as the series reaches its end.