Just some thoughts, NO FACTS HERE.
Ok so lets look at this, if the accused has cuts which may be defensive wounds and he was not the killer, there must be a reason he didn't come forward. I can think of these:
1. His life or his family's lives were threatened should he come forward
2. The killer/killers were someone he knew and he is trying to protect them
3. He thought the truth sounded ridiculous and would not be believed and that he would be thought the killer.
Let's say he and another person commited the crime. For what reason would he have defensive wounds other than receiving them from the victims?
What if the accused and other killers, murdered the parents in order to take CR away. Maybe they wouldn't let her do something or see someone and she said something to one of them that they took far too literally. I remember being a teenager and sometime your parents piss you off so much you say things you don't mean, to them and friend. So what if they killed the parents then went to CR to take her away and she freaked out (as you would). She doesn't want any part of it, the other killer/killers want to get rid of her so she cant go to the police, but the accused doesn't want that, he tries to protect her and get the wounds he received. He wont go to the police as it would be implicating him in two murders.