Oubliette is quite right. If there is a known crime committed and a person or persons fail to report they are culpable to a degree for not informing the police. Now I am sure there are many crimes that go unreported, but this particular one of child abuse, can land some people in very hot water.
I know this due to my own "reporting" of this crime against my children. She, the detective sat there listening, pen in hand, document infront of her........" So, are you willing to make a police report, an official report about this?"
"Yes, why do you think I'm here, just to have a chat?"
"No, I don't think that at all. It's just that we have so many come in and not make it official. When that happens we like to take actions that are in our powers to take".
That was in the early 80s. I had no qualms about what I was about to do. Not one, I wanted action for the future of the children. I wanted them to know they had been defended and I was very sorry not to have seen this side of that man. The point is, that even back then, the police did have a great capacity to involve others if not supplied with the legal go ahead of the parent, guardian or complainant. I know that not much has been done in those years. The things is, they were trying to work at it even then. I'm very aware of how they must have felt frustrated.
So there was always an obligation to report, it rarely happened though.