I think it is down to the parents as so many others have said - trying to re-install respect at school, for the police, etc. will all do nothing unless it comes from and is reinforced in the home.
I have worked a lot with young people and have lost count of the numbers of times parents have come down to the project effing and jeffing about their little darling (incidentally this was a project for children leaving care or accepted as homeless so they hadn't been living with mum/dad!) had a warning letter or something for unacceptable behaviour. The parents were far more abusive, offensive and threatening than any of the young people were - and to give our residents their due, they could often see that too.
But please don't forget - we are talking about a small minority of young people here - that does not make it any the less concerning, but let's not label every young person.