Binro the Heretic - 2017-11-26 According to legend, the guys who wrote this song originally intended it to be a dark tale of a serial killer living next door.
Then they were contracted to score this flick, kept the tune & changed the lyrics to reflect the plot.
badideasinaction - 2017-11-27 Heard something close: according to this: https://www.youtube.com/watch?v=vebZRbZVtYU
It was mistakenly left on the demo tape of possible songs to use for Flashdance, the rest of which were conventional dancey numbers. Director didn't care for the rest but noticed the accidental bonus track and liked the sound so it was rewritten.