Marty had lived an eventful nine years. He had been shuffled from one foster home to another. Eventually he was claimed and adopted by his biological parents who regretted giving him up nine years earlier. What became obvious very quickly was the reason they had given Marty up for adoption in the first place: they were incompetent parents.
Neither parent worked. Mom got drunk every night. Dad was hardly ever home; he was out doing whatever it is that grownups do. Marty was always hungry. In many ways he was the only sensible person in the household.
Anyway, he had no trouble getting rid of the bodies. It was the tell-tale kitchen carving knife he was most worried about.