After reading @villa4europe 's post about John Wayne Gacy on the TV thread I would recommend the film/mini series called 'To Catch a Killer' that covers the story. Gacy was very much a mini Jimmy Saville, working for children's charity's, respected for employing young men who may have been off the beaten track, pillar of the community etc.
It is a long film, over three hours and was released originally as a two part offering but well worth the investment. Brian Dennehy is superb as Gacy and Michael Riley as the man putting all the clues together is his perfect foil.