The Lutzes stated that their youngest daughter, Missy, had an imaginary friend in the form of an enormous pig named Jodie who spoke only to her. They also claimed to witness a pair of glowing red animal eyes staring at them through the windows and found enormous hoof prints outside the house that were unexplained. The fireplace bit came from another assertation by the Lutzes that husband and wife saw a demon's head appear to them in the fireplace and that the burnt image lingered on the wall after the fire had died.
I think my old chum may have also been combining some bits from another infamous New York-based "occult" incident, the "Son of Sam" murders carried out by knucklehead David Berkowitz. Berkowitz believed a dog spoke to him and instructed him on how and who to kill during his crime spree. Satanism was an excuse for many shitheads in the '70s and '80s to kill groups of people willy-nilly and with care-free abandon.