This is the case you're thinking of. It instantly popped into my head because I just saw it profiled on the TV special, "Too Young to Kill: 15 Shocking Crimes".
http://en.wikipedia.org/wiki/Josh_Phillips_(murderer)
What a stupid, senseless crime! The kid had injured the young girl and because he thought that would get him trouble with his domineering father, he thought the best solution was to kill her and hide the body under his bed! I at least have to give credit to his mother for calling the police after she discovered the body, as I'm sure some parents might have been tempted to dispose of it and help cover up the child crime, and that poor girl's family might have never gotten closure.