The character of The Chopper in Causes Unknown – an ambiguously sexual serial killer with a chameleon-like ability to lure his victims – might seem to be an exaggeration if it weren’t for the existence of real-life pathologic al killers like John Wayne Gacy. Gacy, some of you may remember, raped and killed at least 33 teenage boys and young men between 1972 and 76 – and got away with it for many years. He used to be known as the ‘Killer Clown’ because he liked to dress up as Pogo the Clown at charitable events and children’s parties.  The Chopper was inspired, if that’s the word for it, by two cases that provoked outrage and horror in the Philadelphia area in the 1980s.