In 1978 the grisly discovery of a crudely buried collection of skeletons beneath a house in Illinois led police to one of the most notorious serial killers in US history: John Wayne Gacy aka the ‘Killer Clown’. Accused of 33 murders, Gacy was known for his appearances at charitable events and children’s parties dressed as ‘Pongo the Clown’.

How forensic methods first developed after the murder of French businessman Charles Lafarge in 1840 helped catch serial poisoner Michael Swango in the early 1990s.