Wasn't "The Candy Man" one such Ronald Clark O'Brien, who poisoned his son on Halloween with Pixy Stix laced with cyanide circa 1974?
I remember the Dean Allen Corll case...he was killed by one of his accomplices, Elmer Wayne Henley, who is serving a life term in prison. Those two (and one other actor, if I remember right) were responsible by at least 30 abduction/murders, as you point out, but I don't recall that Corll had a nickname such as "The Candy Man." I do remember the case being referred to as the "Boathouse Murders," because many of the victims were buried in the dirt floor of a boat storage shed.
You are correct. Corll didn't have a candy factory either. But, he did have a boatshed.