Sounds like this child had no father, the mother wanted to wash her hands of any responsibility for raising a boy to be a man, and the grandfather may have had some motive for wanting the old lady dead, like a forged life insurance policy; either that, or he delayed calling 911 so he could think of what to do because his blood had killed someone on his watch. Or, he killed him and is sandbagging the kid. What a tragedy for the boy. But he must be tried and sentenced, if it is determined that he really was the killer.
Should read "he killed her." Sorry about that.