There are three ways to think about the relationship between the legal and moral realms. First, either they perfectly coincide so that everything legal is moral (and everything illegal is immoral), or second,they don’t overlap at all or, third,they partially overlap so that some actions, such as murder would be both illegal and immoral while other actions, such as adultery might be immoral without being illegal and yet other actions, like insider trading, might be illegal without being immoral.The history of man shows some interesting differences between societies and within societies over time in what is and what isn’t adjudged to be a matter of both legal and moral concern.
I would think that most people would consider the rejection of murder to be something that falls within the scope of both legality and morality. The NAP, then, would be a moral principle which ought to (and frequently does) form the core of the law of most functioning societies. What is unique to libertarianism (at least, libertarianism of the Rothbardian variety) is that it holds that only actions prohibited by the NAP ought to be prohibited by all and every society. Everything else is a matter of regulation to which one is free to subscribe or not as one sees fit. The rules and regulations of a chess club only apply to its members and you’re free to join or leave as you choose.