To my understand, it was estimate that Gacy killed close to 50 +

There was actually a document i saw recently about him

During a three-year-period, Gacy went on to viciously torture, rape and murder more than thirty other young men, who would later be discovered under the floorboards of his home and countless morein the local river.

Yeah i wouldn't doubt there are some victims whom were ever recovered and most likely never will do. I always thought that clown from 'IT' was from the idea of Gacy. I also will admit i was scared of clowns for awhile after seeing that movie lol