Who is John Byro? Why did he not accuse the boys of stealing his white horse?

John Byro, in this story, is the original owner of the beautiful white horse which is mentioned in the title and which is stolen by the cousin of the narrator. We are told that John Byro is an Assyrian by birth, but he has learned Armenian in order to be able to speak to his neighbors.
Byro knows that the horse the boys have is his horse. He looks into its mouth and tries to make it obvious that he knows what has happened—he says he would swear this were his horse were it not for the renowned honesty and integrity of the boys' family. He seems to want the boys to confess to what they have done and return the horse of their own accord so he doesn't have to get them in trouble with their family. It could also be that Byro, who is a foreigner, does not want to create trouble for himself by throwing around accusations within this community, to which he does not belong.
The boys do indeed feel guilty, and they return the horse to John Byro overnight.