A child of 10 is not capable of forming judgements independently from the adults who have shaped its formative experiences. This is because the myelin sheath is not developed until much later. For this reason, if the adults in the child's life are modeling bad behavior, even if the child is told that such behavior is bad, the child will not fully understand the "badness" of it, nor the ramifications of bad behaviors. I don't know anything about this particular child's home environment while growing up, but there are many reasons why a child of 10 could be unable to form appropriate judgements.