The Kalispell, Montana police are not charging Mr Harper with any crime. The reason is the "castle doctrine", newly added to Montana law. If someone has merely "reasonable belief" that he will be assaulted, even by an unarmed assailant, in his home, he may use deadly force in response. The traditional arguments quickly flow from both sides: from the police and gun-control advocates, that this is a "license to kill", from the pro-gun lobby, that it deters crime.