The guy was 6 foot 2 inches tall. He either left the place by his own power, was removed from the scene by two or more people, got into a strangers car and was somehow overpowered despite his size….. or…… he simply fell into a crack and was not discovered before construction continued on that building.
There was a case in NY where a woman fell through her attic into a space between the walls of her house, and survived there for several days before dying. Nobody heard her, nobody noticed she was gone. Eventually they found her bones behind the wall when the new owners of her house went to remodel. This situation, being trapped but alive somewhere nearby, would explain why cadaver dogs didn’t pick up a scent.