Pit bull attack

Apparently a 17 year old boy told his 65 lbs pit bull to "sic" two young boys with one boy suffering severe facial lacerations from injuries occurring thereafter. The 17 year old boy is being charged with an assault producing great bodily injury. How does the district attorney prove that the actual attack was the result of a highly trained animal responding to an order to attack as opposed to a coincidental action by the dog following a statement by its human? I would assume the former could serve as the criminal intent for a conviction whereas the criminal intent would be nearly impossible to show in the latter. As an aside the 17 year old faces 8 years in the big house. A neighbor says that the two young boys were bratty. The 17 year old tried to hide the dog. When the police found the dog it attacked them. See here for an article on the case.