BONUS: John Wayne Gacy (Mark of a Serial Killer)

We are bringing you a special bonus episode featuring a case from Oxygen's hit series, “Mark of a Serial Killer.” Watch Mark of a Serial Killer on Sundays at 7/6c on Oxygen! A rash of young men goes missing around Chicago during the 1970s; when bodies start washing up in the river, a pattern emerges; a small piece of evidence leads police to the home of a model citizen, where his furnace puts the suspect in the hot seat.