He's one of the most-notorious serial killers in American history and the inspiration for numerous slasher movies.

'Pogo the clown' by day and mass murderer by night, when John Wayne Gacy first killed a man at his Chicago ranch house after sex, he soon realised how easy it would be to hunt, lure and kill his prey.

Thirty-three murders later, police finally moved in on the sadistic sexual predator and uncovered his sickening series of crimes. But what turned a seemingly ordinary man into a prolific killer?

Clodagh Meaney chats with Brad Hunter, author of 'Inside the mind of John Wayne Gacy, about Gacy's motivations, how his childhood shaped him and why, to this day, some of the victims remain unknown.

Crime World, with Nicola Tallant, is a weekly Iri…