Richard Kuklisnki, known as the 'Iceman,' claimed to have killed up to 250 in his three-decade-long career as a hitman for the mafia, all of which he kept separate from his average middle-class existence. How much of Kuklisnki's psychopathic personality was passed on by his parents? And how much of his traumatic upbringing was invented by Kuklinski as a way of rationalizing his crimes?

In December 2012, 20-year-old Adam Lanza killed his mother Nancy before driving to Sandy Hook Elementary School and shooting dead 20 children and six teachers in one of the bloodiest mass shootings in American history. How much is Nancy to blame for keeping an arsenal of weapons in the family home with a mentally disturbed son for whom she refused to seek comprehensive treatment?

One of Poland's most notorious serial killers, Leszek Pekalski confessed to murdering dozens of people - men, women, and children, who were mostly savagely bludgeoned to death before being raped - although he later recanted all but one of his confessions. What role did his violent mother's heavy drinking while pregnant and later abuse and neglect play in Pekalski's evolution?

Serial child-killer Robert Black worked as a delivery driver, preying on young girls up and down the country. Black's own childhood was fraught with violence and abandonment. MacIntyre and Dr Elizabeth Yardley piece together Black's fractured upbringing and explore whether these early psychological traumas were the triggers which transformed Black into the depraved monster he became.

One of Britain's most infamous killers, Dennis Nilsen murdered 15 young men, some as young as 14,in London during the late seventies and early eighties. Nilsen held on to the corpses of his victims for weeks on end, talking to them on his return home from work and sleeping beside them. But what led this seemingly normal civil servant to start killing for company?

Joachim Knychala, the Polish serial killer who earned the ghoulish nickname 'Frankenstein,' attacked his victims with an axe, butchering and desecrating their bodies after death. MacIntyre and criminologist Dr Elizabeth Yardley explore Knychala's twisted relationship with his mother and grandmother to discover whether they were the cause of his murderous misogyny.

Dr Harold Shipman, was Britain's most prolific serial killer with at least 215 known victims. Was Shipman simply addicted to murder, playing God by killing many of his elderly female patients with overdoses of morphine, or did his upbringing and the circumstances of his mother's death turn him into a mass murderer?

The case of Jed Allen, a young man who on the surface had a happy, stable life. Yet in May 2015 he would kill his mother, step-father and six year old half-sister in a brutal knife attack. MacIntyre and criminologist Dr Elizabeth Yardley explore Jed's dysfunctional childhood years with his mother to discover the trigger that led him to commit family annihilation.