Number of victims: 7+
Date of murders: 1996 - 2005
Method of murder: Bludgeoning / Hanging
Location: Washington / California / Idaho
A horrifically depraved child killer, Duncan first came to national media attention in May 2005, when he murdered Brenda Groene, 40; her son Slade, 13; and her boyfriend, Mark McKenzie, 37. He then kidnapped Brenda Groene's two younger children, Dylan, 9, and Shasta, 8.
A massive search was launched for the missing children but Duncan had driven them deep into the dense forests surrounding Coeur d'Alene, Idaho. Their whereabouts would remain a mystery until July 2, when Duncan casually walked into a Denny's restaurant in Coeur d'Alene with Shasta in tow. The child was recognized by staff who called the police. Duncan was arrested at the scene.
It emerged that Duncan had held the children at a makeshift camp in the woods for over a month, raping and abusing them. When Dylan became too much of a burden he killed him by hanging him from a tree.
And that wasn't the full extent of Duncan's criminal career. He had a long arrest record, mainly for raping and molesting children. He was also implicated in three more child murders, in Washington State and in California.
Duncan faced both state and federal charges. On the state charges he received three life sentences while the federal charges (for kidnapping Shasta and Dylan Groene and for murdering Dylan) saw him sentenced to death.